[PATCH 4.16 239/272] audit: return on memory error to avoid null pointer dereference

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Guy Briggs <rgb@xxxxxxxxxx>

[ Upstream commit 23138ead270045f1b3e912e667967b6094244999 ]

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@xxxxxxxxxx>
[PM: not necessary (other funcs check for NULL), but a good practice]
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/audit.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1058,6 +1058,8 @@ static void audit_log_feature_change(int
 		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,