[ 55/76] fs: handle failed audit_log_start properly

[Greg Kroah-Hartman]

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

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

From: Sasha Levin <sasha.levin@xxxxxxxxxx>

commit d1c7d97ad58836affde6e39980b96527510b572e upstream.

audit_log_start() may return NULL, this is unchecked by the caller in
audit_log_link_denied() and could cause a NULL ptr deref.

Introduced by commit a51d9eaa ("fs: add link restriction audit reporting").

Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
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
@@ -1466,6 +1466,8 @@ void audit_log_link_denied(const char *o
 
 	ab = audit_log_start(current->audit_context, GFP_KERNEL,
 			     AUDIT_ANOM_LINK);
+	if (!ab)
+		return;
 	audit_log_format(ab, "op=%s action=denied", operation);
 	audit_log_format(ab, " pid=%d comm=", current->pid);
 	audit_log_untrustedstring(ab, current->comm);


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