audit: return on memory error to avoid null pointer dereference

If there is a memory allocation error when trying to change an audit
kernel feature value, the ignored allocation error will trigger a NULL
pointer dereference oops on subsequent use of that pointer.  Return
instead.

Passes audit-testsuite.
See: https://github.com/linux-audit/audit-kernel/issues/76

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: not necessary (other funcs check for NULL), but a good practice]
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 5c2544984375..2de74be7cef5 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1059,6 +1059,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
                 return;
 
         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
+        if (!ab)
+                return;
         audit_log_task_info(ab, current);
         audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
                          audit_feature_names[which], !!old_feature, !!new_feature,