Re: [PATCH v4 1/5] xfs: fix capability check in xfs

[sergeh@kernel.org]

On Tue, Aug 04, 2026 at 11:45:51AM +0200, cem@kernel.org wrote:
> From: Carlos Maiolino <cem@kernel.org>
> 
> An user reported a bug where he managed to evade group's quota
> by changing a file's gid to a different group id the same user
> belonged to, even though quotas were enforced on both gids and the
> file's size was big enough to exceed the quota's hardlimit.
> 
> Commit eba0549bc7d1 replaced a capable() call by a
> has_capability_noaudit() to prevent unnecessary selinux audit messages.
> Turns out that both calls have slightly different semantics even though
> their documentation seems similar. Where in a nutshell:
> 
> capable() - Tests the task's effective credentials
> has_ns_capability_noaudit() - Tests the task's real credentials
> 
> This most of the time has no practical difference but in some cases like
> changing attrs (specifically group id in this case) through a NFS client
> this will allow the quota code to use XFS_QMOPT_FORCE_RES, effectively
> bypassing quota accounting checks.
> 
> Using instead ns_capable_noaudit() should fix this issue and prevent
> selinux audit messages.

Hi,

this makes perfect sense, but since you say "should fix this issue",
did you have a chance to set up a reproducer, and verify?

> This also fix the remaining calls to has_capability_noaudit()
> 
> Fixes: eba0549bc7d1 ("xfs: don't generate selinux audit messages for capability testing")
> Cc: <stable@vger.kernel.org> # v5.18
> Reported-by: Dr. Thomas Orgis <thomas.orgis@uni-hamburg.de>
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Reviewed-by: Serge Hallyn <sergeh@kernel.org>

thanks,
-serge

> ---
>  fs/xfs/xfs_fsmap.c | 2 +-
>  fs/xfs/xfs_ioctl.c | 2 +-
>  fs/xfs/xfs_iops.c  | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
> index b6a3bc9f143c..7c79fbe0a74c 100644
> --- a/fs/xfs/xfs_fsmap.c
> +++ b/fs/xfs/xfs_fsmap.c
> @@ -1175,7 +1175,7 @@ xfs_getfsmap(
>  		return -EINVAL;
>  
>  	use_rmap = xfs_has_rmapbt(mp) &&
> -		   has_capability_noaudit(current, CAP_SYS_ADMIN);
> +		   ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);
>  	head->fmh_entries = 0;
>  
>  	/* Set up our device handlers. */
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 1b53701bebea..1a8af827dde1 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -647,7 +647,7 @@ xfs_ioctl_setattr_get_trans(
>  		goto out_error;
>  
>  	error = xfs_trans_alloc_ichange(ip, NULL, NULL, pdqp,
> -			has_capability_noaudit(current, CAP_FOWNER), &tp);
> +			ns_capable_noaudit(&init_user_ns, CAP_FOWNER), &tp);
>  	if (error)
>  		goto out_error;
>  
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 6339f4956ecb..7a8c77fdcf68 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -835,7 +835,7 @@ xfs_setattr_nonsize(
>  	}
>  
>  	error = xfs_trans_alloc_ichange(ip, udqp, gdqp, NULL,
> -			has_capability_noaudit(current, CAP_FOWNER), &tp);
> +			ns_capable_noaudit(&init_user_ns, CAP_FOWNER), &tp);
>  	if (error)
>  		goto out_dqrele;
>  
> -- 
> 2.55.0
>