On Fri, Aug 26, 2022 at 4:44 AM Christian Brauner [off-list ref] wrote:

On Fri, Aug 19, 2022 at 02:50:57PM -0400, Paul Moore wrote:

quoted

On Tue, Aug 16, 2022 at 6:12 PM Paul Moore [off-list ref] wrote:

quoted

On Fri, Jul 8, 2022 at 5:35 AM Ondrej Mosnacek [off-list ref] wrote:

quoted

Since userfaultfd doesn't implement a write operation, it is more
appropriate to open it read-only.

When userfaultfds are opened read-write like it is now, and such fd is
passed from one process to another, SELinux will check both read and
write permissions for the target process, even though it can't actually
do any write operation on the fd later.

Inspired by the following bug report, which has hit the SELinux scenario
described above:
https://bugzilla.redhat.com/show_bug.cgi?id=1974559

Reported-by: Robert O'Callahan <redacted>
Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---

Resending as the last submission was ignored for over a year...

https://lore.kernel.org/lkml/20210624152515.1844133-1-omosnace@redhat.com/T/ (local)

I marked this as RFC, because I'm not sure if this has any unwanted side
effects. I only ran this patch through selinux-testsuite, which has a
simple userfaultfd subtest, and a reproducer from the Bugzilla report.

Please tell me whether this makes sense and/or if it passes any
userfaultfd tests you guys might have.

 fs/userfaultfd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

VFS folks, any objection to this patch?  It seems reasonable to me and
I'd really prefer this to go in via the vfs tree, but I'm not above
merging this via the lsm/next tree to get someone in vfs land to pay
attention to this ...

Okay, final warning, if I don't see any objections to this when I make
my patch sweep next week I'm going to go ahead and merge this via the
LSM tree.

Makes sense,
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>

Merged into lsm/next, thanks all.

-- 
paul-moore.com