On Thu, May 20, 2021 at 3:58 AM Christian Brauner
[off-list ref] wrote:

On Wed, May 19, 2021 at 04:00:21PM -0400, Richard Guy Briggs wrote:

quoted

The openat2(2) syscall was added in kernel v5.6 with commit fddb5d430ad9
("open: introduce openat2(2) syscall")

Add the openat2(2) syscall to the audit syscall classifier.

Link: https://github.com/linux-audit/audit-kernel/issues/67
Signed-off-by: Richard Guy Briggs <redacted>
Link: https://lore.kernel.org/r/f5f1a4d8699613f8c02ce762807228c841c2e26f.1621363275.git.rgb@redhat.com (local)
---
 arch/alpha/kernel/audit.c           | 2 ++
 arch/ia64/kernel/audit.c            | 2 ++
 arch/parisc/kernel/audit.c          | 2 ++
 arch/parisc/kernel/compat_audit.c   | 2 ++
 arch/powerpc/kernel/audit.c         | 2 ++
 arch/powerpc/kernel/compat_audit.c  | 2 ++
 arch/s390/kernel/audit.c            | 2 ++
 arch/s390/kernel/compat_audit.c     | 2 ++
 arch/sparc/kernel/audit.c           | 2 ++
 arch/sparc/kernel/compat_audit.c    | 2 ++
 arch/x86/ia32/audit.c               | 2 ++
 arch/x86/kernel/audit_64.c          | 2 ++
 include/linux/auditsc_classmacros.h | 1 +
 kernel/auditsc.c                    | 3 +++
 lib/audit.c                         | 4 ++++
 lib/compat_audit.c                  | 4 ++++
 16 files changed, 36 insertions(+)

...

quoted

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index d775ea16505b..3f59ab209dfd 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c

@@ -76,6 +76,7 @@
 #include <linux/fsnotify_backend.h>
 #include <uapi/linux/limits.h>
 #include <uapi/linux/netfilter/nf_tables.h>
+#include <uapi/linux/openat2.h>

 #include "audit.h"

@@ -196,6 +197,8 @@ static int audit_match_perm(struct audit_context *ctx, int mask)
              return ((mask & AUDIT_PERM_WRITE) && ctx->argv[0] == SYS_BIND);
      case AUDITSC_EXECVE:
              return mask & AUDIT_PERM_EXEC;
+     case AUDITSC_OPENAT2:
+             return mask & ACC_MODE((u32)((struct open_how *)ctx->argv[2])->flags);

That's a lot of dereferncing, casting and masking all at once. Maybe a
small static inline helper would be good for the sake of legibility? Sm
like:

static inline u32 audit_openat2_acc(struct open_how *how, int mask)
{
        u32 flags = how->flags;
        return mask & ACC_MODE(flags);
}

but not sure. Just seems more legible to me.
Otherwise.

I'm on the fence about this.  I understand Christian's concern, but I
have a bit of hatred towards single caller functions like this.  Since
this function isn't really high-touch, and I don't expect that to
change in the near future, let's leave the casting mess as-is.

-- 
paul moore
www.paul-moore.com