From: Kirill A. Shutemov <hidden> Date: 2015-01-26 12:48:08
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
quoted hunk
---
Changes in v2: Removed the follow_link() stub that returned -EPERM if
the caller didn't have CAP_SYS_ADMIN, since the caller
in my chroot() scenario gets -EACCES anyway.
fs/proc/base.c | 18 ------------------
1 file changed, 18 deletions(-)
--
1.8.1
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On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
From: Andrew Morton <akpm@linux-foundation.org> Date: 2015-01-26 23:43:52
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
On Mon, Jan 26, 2015 at 3:43 PM, Andrew Morton
[off-list ref] wrote:
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
If akpm's comments weren't clear: this needs to be fixed. Everything
in /proc should appear in Documentation.
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
How is mmap offset represented in this output?
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Both maps and map_files uses ptrace_may_access (via mm_acces) with
PTRACE_MODE_READ, so I'm happy from a info leak perspective.
Are mount namespaces handled in this output?
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
From: Kirill A. Shutemov <hidden> Date: 2015-01-27 00:20:36
On Mon, Jan 26, 2015 at 03:43:46PM -0800, Andrew Morton wrote:
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
Almost.
IIUC, before we haven't had a way to retrieve a file descriptor from
mapped file if it was closed and not accessible for direct re-open. Like
in chroot case or unlink after close.
I'm not sure what security implications this move has, if any. I don't see
anything obviously dangerous.
--
Kirill A. Shutemov
On Mon, Jan 26, 2015 at 03:43:46PM -0800, Andrew Morton wrote:
quoted
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
yup, I managed to forget CC him.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
Sigh. Imagine, for some reason I though we've the docs for that
entry, probably i though that way because of many fdinfo snippets
i've putted into /proc docs. my bad, sorry. I'll try to prepare
docs today.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
I didn't find any bugs in map-files (and we use it for long time already)
so I think it is safe.
From: Andrew Morton <akpm@linux-foundation.org> Date: 2015-01-27 06:50:52
On Tue, 27 Jan 2015 09:46:47 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
I didn't find any bugs in map-files (and we use it for long time already)
so I think it is safe.
You've been using map_files the way it was supposed to be used so no,
any bugs won't show up. What happens if you don your evil black hat
and use map_files in ways that weren't anticipated? Attack it?
On Mon, Jan 26, 2015 at 10:50:23PM -0800, Andrew Morton wrote:
On Tue, 27 Jan 2015 09:46:47 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
I didn't find any bugs in map-files (and we use it for long time already)
so I think it is safe.
You've been using map_files the way it was supposed to be used so no,
any bugs won't show up. What happens if you don your evil black hat
and use map_files in ways that weren't anticipated? Attack it?
Hard to say, Andrew. If I found a way to exploit this feature for
bad purpose for sure I would patch it out. At the moment I don't
see any. Touching another process memory via file descriptor
allows one to modify its contents but you have to be granted
ptrace-may-access which i consider as enough for security.
If akpm's comments weren't clear: this needs to be fixed. Everything
in /proc should appear in Documentation.
I'll do that.
quoted
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Both maps and map_files uses ptrace_may_access (via mm_acces) with
PTRACE_MODE_READ, so I'm happy from a info leak perspective.
Are mount namespaces handled in this output?
Could you clarify this moment, i'm not sure i get it.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
If akpm's comments weren't clear: this needs to be fixed. Everything
in /proc should appear in Documentation.
I'll do that.
quoted
quoted
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Both maps and map_files uses ptrace_may_access (via mm_acces) with
PTRACE_MODE_READ, so I'm happy from a info leak perspective.
Are mount namespaces handled in this output?
Could you clarify this moment, i'm not sure i get it.
I changed how I asked this question in my review of the documentation,
but it looks like these symlinks aren't "regular" symlinks (that are
up to the follower to have access to the file system path shown), but
rather they bypass VFS. As a result, I'm wondering how things like
mount namespaces might change this behavior: what is shown, the path
from the perspective of the target, or from the viewer (which may be
in separate mount namespaces).
-Kees
quoted
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
On Tue, Jan 27, 2015 at 11:53:19AM -0800, Kees Cook wrote:
quoted
quoted
Are mount namespaces handled in this output?
Could you clarify this moment, i'm not sure i get it.
I changed how I asked this question in my review of the documentation,
but it looks like these symlinks aren't "regular" symlinks (that are
up to the follower to have access to the file system path shown), but
rather they bypass VFS. As a result, I'm wondering how things like
mount namespaces might change this behavior: what is shown, the path
from the perspective of the target, or from the viewer (which may be
in separate mount namespaces).
I must admit I personally didn't investigating how mount namespaces
might itercat with map-files. Pavel, could you share the thoughts?
From: Pavel Emelyanov <hidden> Date: 2015-01-27 21:47:36
quoted
quoted
Are mount namespaces handled in this output?
Could you clarify this moment, i'm not sure i get it.
I changed how I asked this question in my review of the documentation,
but it looks like these symlinks aren't "regular" symlinks (that are
up to the follower to have access to the file system path shown), but
rather they bypass VFS. As a result, I'm wondering how things like
mount namespaces might change this behavior: what is shown, the path
from the perspective of the target, or from the viewer (which may be
in separate mount namespaces).
These work just like the /proc/$pid/fd/$n links do. When you readlink
on it the d_path() is called which walks up the dentry/vfsmnt tree
until it reaches either current root or the global one. For "another"
mount namespace case it produces the path relative to this namespace's
root.
Thanks,
Pavel
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
Thanks,
Calvin
On Tue, Jan 27, 2015 at 8:38 PM, Calvin Owens [off-list ref] wrote:
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
quoted
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
My concern here is that fd/* are connected as streams, and while that
has a certain level of badness as an external-to-the-process attacker,
PTRACE_MODE_READ is much weaker than PTRACE_MODE_ATTACH (which is
required for access to /proc/N/mem). Since these fds are the things
mapped into memory on a process, writing to them is a subset of access
to /proc/N/mem, and I don't feel that PTRACE_MODE_READ is sufficient.
-Kees
--
Kees Cook
Chrome OS Security
On Thursday 01/29 at 17:30 -0800, Kees Cook wrote:
On Tue, Jan 27, 2015 at 8:38 PM, Calvin Owens [off-list ref] wrote:
quoted
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
quoted
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
My concern here is that fd/* are connected as streams, and while that
has a certain level of badness as an external-to-the-process attacker,
PTRACE_MODE_READ is much weaker than PTRACE_MODE_ATTACH (which is
required for access to /proc/N/mem). Since these fds are the things
mapped into memory on a process, writing to them is a subset of access
to /proc/N/mem, and I don't feel that PTRACE_MODE_READ is sufficient.
If you haven't done close() on a mmapped file, doesn't fd/* allow the
same access to the corresponding regions of memory? Or am I missing
something?
But that said, I can't think of any reason making it MODE_ATTACH would
be a problem. Would you rather that be enforced on follow_link() like
the original patch did, or enforce it for the whole directory?
Thanks,
Calvin
From: Austin S Hemmelgarn <hidden> Date: 2015-02-02 14:01:35
On 2015-01-30 20:58, Calvin Owens wrote:
On Thursday 01/29 at 17:30 -0800, Kees Cook wrote:
quoted
On Tue, Jan 27, 2015 at 8:38 PM, Calvin Owens [off-list ref] wrote:
quoted
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
quoted
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
My concern here is that fd/* are connected as streams, and while that
has a certain level of badness as an external-to-the-process attacker,
PTRACE_MODE_READ is much weaker than PTRACE_MODE_ATTACH (which is
required for access to /proc/N/mem). Since these fds are the things
mapped into memory on a process, writing to them is a subset of access
to /proc/N/mem, and I don't feel that PTRACE_MODE_READ is sufficient.
If you haven't done close() on a mmapped file, doesn't fd/* allow the
same access to the corresponding regions of memory? Or am I missing
something?
But that said, I can't think of any reason making it MODE_ATTACH would
be a problem. Would you rather that be enforced on follow_link() like
the original patch did, or enforce it for the whole directory?
Whole directory would probably be better, as even just the mapped ranges
could be considered sensitive information. Ideally, the check should be
done on both follow_link(), and the directory itself.
From: Andy Lutomirski <luto@amacapital.net> Date: 2015-02-02 20:17:06
On Fri, Jan 30, 2015 at 5:58 PM, Calvin Owens [off-list ref] wrote:
On Thursday 01/29 at 17:30 -0800, Kees Cook wrote:
quoted
On Tue, Jan 27, 2015 at 8:38 PM, Calvin Owens [off-list ref] wrote:
quoted
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
quoted
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
My concern here is that fd/* are connected as streams, and while that
has a certain level of badness as an external-to-the-process attacker,
PTRACE_MODE_READ is much weaker than PTRACE_MODE_ATTACH (which is
required for access to /proc/N/mem). Since these fds are the things
mapped into memory on a process, writing to them is a subset of access
to /proc/N/mem, and I don't feel that PTRACE_MODE_READ is sufficient.
If you haven't done close() on a mmapped file, doesn't fd/* allow the
same access to the corresponding regions of memory? Or am I missing
something?
But if you have called close(), then you can't currently do things
like ftruncate or ioctl on the mapped file. These things don't
persist across execve(), but the do persist across calls to setresuid,
etc that drop privileges. The latter part makes me a tiny bit
nervous.
It also might be worth checking for drivers or arch code that creates
vmas that are backed by a different struct file than the struct file
that was mmapped in the first place.
--Andy
On Monday 02/02 at 12:16 -0800, Andy Lutomirski wrote:
On Fri, Jan 30, 2015 at 5:58 PM, Calvin Owens [off-list ref] wrote:
quoted
On Thursday 01/29 at 17:30 -0800, Kees Cook wrote:
quoted
On Tue, Jan 27, 2015 at 8:38 PM, Calvin Owens [off-list ref] wrote:
quoted
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
quoted
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
My concern here is that fd/* are connected as streams, and while that
has a certain level of badness as an external-to-the-process attacker,
PTRACE_MODE_READ is much weaker than PTRACE_MODE_ATTACH (which is
required for access to /proc/N/mem). Since these fds are the things
mapped into memory on a process, writing to them is a subset of access
to /proc/N/mem, and I don't feel that PTRACE_MODE_READ is sufficient.
If you haven't done close() on a mmapped file, doesn't fd/* allow the
same access to the corresponding regions of memory? Or am I missing
something?
But if you have called close(), then you can't currently do things
like ftruncate or ioctl on the mapped file. These things don't
persist across execve(), but the do persist across calls to setresuid,
etc that drop privileges. The latter part makes me a tiny bit
nervous.
Hmm, in that scenario you would have to open() the map_files symlink,
and since you've dropped privileges that would only succeed if the user
you dropped to has permission to access that file anyway, right?
In the deleted file case it does actually allow something that used to
be impossible, but relying on open/map/close/unlink to prevent a user
from opening a file they have permission to open is just buggy in
general.
But, O_TMPFILE lets you end up in that position without the race. The
manpage says that O_TMPFILE files "can never be reached via any
pathname", which isn't strictly true since you can get them from fd/* in
proc. But if you close() after mapping it they are currently truly
inaccessible via any path, and given the language in the manpage it
seems reasonable that somebody might rely on that and be lazy with the
permissions.
I hadn't thought about O_TMPFILE thing: I'm definitely convinced now
that PTRACE_MODE_ATTACH is the right thing here. But I think having to
reopen the file saves you even if you "leak" maps of files across a call
to setresuid/etc.
It also might be worth checking for drivers or arch code that creates
vmas that are backed by a different struct file than the struct file
that was mmapped in the first place.
Interesting, I'll look into this before I resend.
Thanks,
Calvin
On Monday 02/02 at 09:01 -0500, Austin S Hemmelgarn wrote:
On 2015-01-30 20:58, Calvin Owens wrote:
quoted
On Thursday 01/29 at 17:30 -0800, Kees Cook wrote:
quoted
On Tue, Jan 27, 2015 at 8:38 PM, Calvin Owens [off-list ref] wrote:
quoted
On Monday 01/26 at 15:43 -0800, Andrew Morton wrote:
quoted
On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov [off-list ref] wrote:
quoted
On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote:
quoted
On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
quoted
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.
This is the main (actually only) justification for the patch, and it it
far too thin. What does "not needed" mean. Why can't people just use
/proc/pid/maps?
The biggest difference is that if you do something like this:
fd = open("/stuff", O_BLAH);
map = mmap(NULL, 4096, PROT_BLAH, MAP_SHARED, fd, 0);
close(fd);
unlink("/stuff");
...then map_files/ gives you a way to get a file descriptor for
"/stuff", which you couldn't do with /proc/pid/maps.
It's also something of a win if you just want to see what is mapped at a
specific address, since you can just readlink() the symlink for the
address range you care about and it will go grab the appropriate VMA and
give you the answer. /proc/pid/maps requires walking the VMA tree, which
is quite expensive for processes with many thousands of threads, even
without the O(N^2) issue.
(You have to know what address range you want though, since readdir() on
map_files/ obviously has to walk the VMA tree just like /proc/N/maps.)
quoted
quoted
quoted
quoted
This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.
Signed-off-by: Calvin Owens <redacted>
Cc +linux-api@
Looks good to me, thanks! Though I would really appreciate if someone
from security camp take a look as well.
hm, who's that. Kees comes to mind.
And reviewers' task would be a heck of a lot easier if they knew what
/proc/pid/map_files actually does. This:
akpm3:/usr/src/25> grep -r map_files Documentation
akpm3:/usr/src/25>
does not help.
The 640708a2cff7f81 changelog says:
: This one behaves similarly to the /proc/<pid>/fd/ one - it contains
: symlinks one for each mapping with file, the name of a symlink is
: "vma->vm_start-vma->vm_end", the target is the file. Opening a symlink
: results in a file that point exactly to the same inode as them vma's one.
:
: For example the ls -l of some arbitrary /proc/<pid>/map_files/
:
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
: | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
afacit this info is also available in /proc/pid/maps, so things
shouldn't get worse if the /proc/pid/map_files permissions are at least
as restrictive as the /proc/pid/maps permissions. Is that the case?
(Please add to changelog).
Yes, the only difference is that you can follow the link as per above.
I'll resend with a new message explaining that and the deletion thing.
quoted
There's one other problem here: we're assuming that the map_files
implementation doesn't have bugs. If it does have bugs then relaxing
permissions like this will create new vulnerabilities. And the
map_files implementation is surprisingly complex. Is it bug-free?
While I was messing with it I used it a good bit and didn't see any
issues, although I didn't actively try to fuzz it or anything. I'd be
happy to write something to test hammering it in weird ways if you like.
I'm also happy to write testcases for namespaces.
So far as security issues, as others have pointed out you can't follow
the links unless you can ptrace the process in question, which seems
like a pretty solid guarantee. As Cyrill pointed out in the discussion
about the documentation, that's the same protection as /proc/N/fd/*, and
those links function in the same way.
My concern here is that fd/* are connected as streams, and while that
has a certain level of badness as an external-to-the-process attacker,
PTRACE_MODE_READ is much weaker than PTRACE_MODE_ATTACH (which is
required for access to /proc/N/mem). Since these fds are the things
mapped into memory on a process, writing to them is a subset of access
to /proc/N/mem, and I don't feel that PTRACE_MODE_READ is sufficient.
If you haven't done close() on a mmapped file, doesn't fd/* allow the
same access to the corresponding regions of memory? Or am I missing
something?
But that said, I can't think of any reason making it MODE_ATTACH would
be a problem. Would you rather that be enforced on follow_link() like
the original patch did, or enforce it for the whole directory?
Whole directory would probably be better, as even just the mapped
ranges could be considered sensitive information.
You can already get the ranges that are mapped from /proc/N/maps with
PTRACE_MODE_READ, so that part isn't new information.
Ideally, the check should be done on both follow_link(), and the
directory itself.
Oh, I didn't mean restricting readdir(), I meant restricting any access
through the directory similar to how the original CAP_SYS_ADMIN check
was done.
Thanks,
Calvin