On 03/12/2018 03:29 PM, Serge E. Hallyn wrote:

Quoting Mimi Zohar (zohar@linux.vnet.ibm.com):

quoted

Files on FUSE can change at any point in time without IMA being able
to detect it.  The file data read for the file signature verification
could be totally different from what is subsequently read, making the
signature verification useless.

FUSE can be mounted by unprivileged users either today with fusermount
installed with setuid, or soon with the upcoming patches to allow FUSE
mounts in a non-init user namespace.

This patch sets the SB_I_IMA_UNVERIFIABLE_SIGNATURE flag and when
appropriate sets the SB_I_UNTRUSTED_MOUNTER flag.

Signed-off-by: Mimi Zohar <redacted>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Seth Forshee <redacted>
Cc: Eric W. Biederman <redacted>
Cc: Dongsu Park <redacted>
Cc: Alban Crequy <redacted>
Cc: "Serge E. Hallyn" <serge@hallyn.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

Of course when IMA namespacing hits, you'll want to compare the
sb->s_user_ns to the (~handwaving~) user_ns owning the ima ns
right?

I suppose this would be the only way to enable 'trusted mounters' within 
IMA namespaces. Maybe there could be an additional capability gate that 
would allow one to be a 'trusted mounter' then?

quoted

---
  fs/fuse/inode.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 624f18bbfd2b..ef309958e060 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c

@@ -1080,6 +1080,9 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
  	sb->s_maxbytes = MAX_LFS_FILESIZE;
  	sb->s_time_gran = 1;
  	sb->s_export_op = &fuse_export_operations;
+	sb->s_iflags |= SB_I_IMA_UNVERIFIABLE_SIGNATURE;
+	if (sb->s_user_ns != &init_user_ns)
+		sb->s_iflags |= SB_I_UNTRUSTED_MOUNTER;
  
  	file = fget(d.fd);
  	err = -EINVAL;

-- 
2.7.5