audit: catch possible NULL audit buffers

It's possible for audit_log_start() to return NULL.  Handle it in the
various callers.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: Jeff Layton <jlayton@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Julien Tinnes <jln@google.com>
Cc: Will Drewry <wad@google.com>
Cc: Steve Grubb <sgrubb@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 9 deletions

diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
index e81175ef25f8..642a89c4f3d6 100644
--- a/kernel/audit_tree.c
+++ b/kernel/audit_tree.c
@@ -449,11 +449,26 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
         return 0;
 }
 
+static void audit_log_remove_rule(struct audit_krule *rule)
+{
+        struct audit_buffer *ab;
+
+        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
+        if (unlikely(!ab))
+                return;
+        audit_log_format(ab, "op=");
+        audit_log_string(ab, "remove rule");
+        audit_log_format(ab, " dir=");
+        audit_log_untrustedstring(ab, rule->tree->pathname);
+        audit_log_key(ab, rule->filterkey);
+        audit_log_format(ab, " list=%d res=1", rule->listnr);
+        audit_log_end(ab);
+}
+
 static void kill_rules(struct audit_tree *tree)
 {
         struct audit_krule *rule, *next;
         struct audit_entry *entry;
-        struct audit_buffer *ab;
 
         list_for_each_entry_safe(rule, next, &tree->rules, rlist) {
                 entry = container_of(rule, struct audit_entry, rule);
@@ -461,14 +476,7 @@ static void kill_rules(struct audit_tree *tree)
                 list_del_init(&rule->rlist);
                 if (rule->tree) {
                         /* not a half-baked one */
-                        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
-                        audit_log_format(ab, "op=");
-                        audit_log_string(ab, "remove rule");
-                        audit_log_format(ab, " dir=");
-                        audit_log_untrustedstring(ab, rule->tree->pathname);
-                        audit_log_key(ab, rule->filterkey);
-                        audit_log_format(ab, " list=%d res=1", rule->listnr);
-                        audit_log_end(ab);
+                        audit_log_remove_rule(rule);
                         rule->tree = NULL;
                         list_del_rcu(&entry->list);
                         list_del(&entry->rule.list);