[PATCH 1/1] selinux,smack: don't bypass permissions check in inode_setsecctx hook

[Paul Moore]

On Wed, Aug 28, 2024 at 3:51 PM Scott Mayhew <smayhew at redhat.com> wrote:
>
> Marek Gresko reports that the root user on an NFS client is able to
> change the security labels on files on an NFS filesystem that is
> exported with root squashing enabled.
>
> The end of the kerneldoc comment for __vfs_setxattr_noperm() states:
>
>  *  This function requires the caller to lock the inode's i_mutex before it
>  *  is executed. It also assumes that the caller will make the appropriate
>  *  permission checks.
>
> nfsd_setattr() does do permissions checking via fh_verify() and
> nfsd_permission(), but those don't do all the same permissions checks
> that are done by security_inode_setxattr() and its related LSM hooks do.
>
> Since nfsd_setattr() is the only consumer of security_inode_setsecctx(),
> simplest solution appears to be to replace the call to
> __vfs_setxattr_noperm() with a call to __vfs_setxattr_locked().  This
> fixes the above issue and has the added benefit of causing nfsd to
> recall conflicting delegations on a file when a client tries to change
> its security label.
>
> Reported-by: Marek Gresko <marek.gresko at protonmail.com>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=218809
> Signed-off-by: Scott Mayhew <smayhew at redhat.com>
> ---
>  security/selinux/hooks.c   | 4 ++--
>  security/smack/smack_lsm.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)

Thanks Scott, this looks good to me, but since it touches Smack too
I'd also like to get Casey's ACK on this patch; if for some reason we
don't hear from Casey after a bit I'll go ahead and merge it.
Speaking of merging, since this touches both SELinux and Smack I'll
likely pull this in via the LSM tree, with a marking for the stable
kernels, if anyone has any objections to that please let me know.

-- 
paul-moore.com