Re: [PATCH RESEND] xfs: don't generate selinux audit messages for capability testing

[Ondrej Mosnacek <omosnace@redhat.com>]

On Tue, Mar 1, 2022 at 3:51 AM Darrick J. Wong <djwong@kernel.org> wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> There are a few places where we test the current process' capability set
> to decide if we're going to be more or less generous with resource
> acquisition for a system call.  If the process doesn't have the
> capability, we can continue the call, albeit in a degraded mode.
>
> These are /not/ the actual security decisions, so it's not proper to use
> capable(), which (in certain selinux setups) causes audit messages to
> get logged.  Switch them to has_capability_noaudit.
>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> Cc: Ondrej Mosnacek <omosnace@redhat.com>
> Cc: Dave Chinner <david@fromorbit.com>
> ---
>  fs/xfs/xfs_fsmap.c  |    4 ++--
>  fs/xfs/xfs_ioctl.c  |    2 +-
>  fs/xfs/xfs_iops.c   |    2 +-
>  kernel/capability.c |    1 +
>  4 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
> index 48287caad28b..10e1cb71439e 100644
> --- a/fs/xfs/xfs_fsmap.c
> +++ b/fs/xfs/xfs_fsmap.c
> @@ -864,8 +864,8 @@ xfs_getfsmap(
>             !xfs_getfsmap_is_valid_device(mp, &head->fmh_keys[1]))
>                 return -EINVAL;
>
> -       use_rmap = capable(CAP_SYS_ADMIN) &&
> -                  xfs_has_rmapbt(mp);
> +       use_rmap = xfs_has_rmapbt(mp) &&
> +                  has_capability_noaudit(current, 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 2515fe8299e1..83481005317a 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1189,7 +1189,7 @@ xfs_ioctl_setattr_get_trans(
>                 goto out_error;
>
>         error = xfs_trans_alloc_ichange(ip, NULL, NULL, pdqp,
> -                       capable(CAP_FOWNER), &tp);
> +                       has_capability_noaudit(current, CAP_FOWNER), &tp);
>         if (error)
>                 goto out_error;
>
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index b79b3846e71b..a65217f787cf 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -723,7 +723,7 @@ xfs_setattr_nonsize(
>         }
>
>         error = xfs_trans_alloc_ichange(ip, udqp, gdqp, NULL,
> -                       capable(CAP_FOWNER), &tp);
> +                       has_capability_noaudit(current, CAP_FOWNER), &tp);
>         if (error)
>                 goto out_dqrele;
>
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 46a361dde042..765194f5d678 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -360,6 +360,7 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>  {
>         return has_ns_capability_noaudit(t, &init_user_ns, cap);
>  }
> +EXPORT_SYMBOL(has_capability_noaudit);
>
>  static bool ns_capable_common(struct user_namespace *ns,
>                               int cap,
>

Thank you for respinning the patch[1]! And sorry that I couldn't find
the time to do that :/

Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>

(Yes, we should still clean up and document the capability functions,
but if no one has the energy, let's at least do the minimal fix.)

[1] Link for reference:
https://lore.kernel.org/linux-xfs/20210316173226.2220046-1-omosnace@redhat.com/T/

--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.