Fix quota evasion on xfs and add capable_noaudit

From: Carlos Maiolino <[email protected]>

Hi there.

This is the a new version of the series I've been working on to fix a quota evasion issue on xfs. I've got to jump to more urgent matters before the previous one so my apologies for the time it took to cook this new version.

The changes to this version compared to the previous one are minor, only comments and indentation related. This new version has also been rebased on top of current xfs's for-next branch. A description of the changes between this and the V3 version are below and more detailed on individual patches.

This bug has originally been introduced by accident while turning off audit messages while checking quota limits in xfs by replacing capable() calls by as_capability_noaudit().

This series concatenates both series I sent for xfs and capabilities infrastructure as they are dependent.

The first patch fix the xfs bug in a way that makes it easily portable to older LTS kernels.

From second patch and beyond, it adds a new helper for the capabilities framework named capable_noaudit() which as the same semantics as capable() but without generating audit messages.
The following patches then replaces both generic quota call to capable() and properly update xfs code to use this new helper.

Last but not least this unexport has_capability_noaudit which had been previously exported.

Giving this affects different subsystems, I think it would be easier to pull everything from a single tree (as long as everything is properly reviewed of course).

Serge, Honza, are you guys ok if I pull those patches and send them to Linus through xfs tree so we don't need to split the series?

Also I kept most of the RwB tags from previous versions as there were no code changes but minor context updates to fix the conflicts.

Serge, I removed your RwB on purpose from the patch 2 as I updated the comment, so I want to make sure you are ok with the new comment.

Changelog from the last state of these patches:

Patch2: Add more details to the capable_noaudit documentation specifying
it checks for the process effective capabilities.

Patch4: Fix identation changes introduced in previous versions

Carlos Maiolino (5):
xfs: fix capability check in xfs
capability: Add new capable_noaudit
quota: Don't issue audit messages on quota enforcing
xfs: replace ns_capable_noaudit
capability: unexport has_capability_noaudit

 fs/quota/dquot.c           |  2 +-
 fs/xfs/xfs_fsmap.c         |  3 +--
 fs/xfs/xfs_ioctl.c         |  2 +-
 fs/xfs/xfs_iops.c          |  2 +-
 include/linux/capability.h |  5 +++++
 kernel/capability.c        | 19 ++++++++++++++++++-
 6 files changed, 27 insertions(+), 6 deletions(-)

2.55.0