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>

4 files changed, 27 insertions, 11 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index 40414e9143db..a219998aecc1 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -272,6 +272,8 @@ static int audit_log_config_change(char *function_name, int new, int old,
         int rc = 0;
 
         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
+        if (unlikely(!ab))
+                return rc;
         audit_log_format(ab, "%s=%d old=%d auid=%u ses=%u", function_name, new,
                          old, from_kuid(&init_user_ns, loginuid), sessionid);
         if (sid) {
@@ -619,6 +621,8 @@ static int audit_log_common_recv_msg(struct audit_buffer **ab, u16 msg_type,
         }
 
         *ab = audit_log_start(NULL, GFP_KERNEL, msg_type);
+        if (unlikely(!*ab))
+                return rc;
         audit_log_format(*ab, "pid=%d uid=%u auid=%u ses=%u",
                          task_tgid_vnr(current),
                          from_kuid(&init_user_ns, current_uid()),
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);
diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index 4a599f699adc..22831c4d369c 100644
--- a/kernel/audit_watch.c
+++ b/kernel/audit_watch.c
@@ -240,6 +240,8 @@ static void audit_watch_log_rule_change(struct audit_krule *r, struct audit_watc
         if (audit_enabled) {
                 struct audit_buffer *ab;
                 ab = audit_log_start(NULL, GFP_NOFS, AUDIT_CONFIG_CHANGE);
+                if (unlikely(!ab))
+                        return;
                 audit_log_format(ab, "auid=%u ses=%u op=",
                                  from_kuid(&init_user_ns, audit_get_loginuid(current)),
                                  audit_get_sessionid(current));
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 3e46d1dec613..a371f857a0a9 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1464,14 +1464,14 @@ static void show_special(struct audit_context *context, int *call_panic)
                         audit_log_end(ab);
                         ab = audit_log_start(context, GFP_KERNEL,
                                              AUDIT_IPC_SET_PERM);
+                        if (unlikely(!ab))
+                                return;
                         audit_log_format(ab,
                                 "qbytes=%lx ouid=%u ogid=%u mode=%#ho",
                                 context->ipc.qbytes,
                                 context->ipc.perm_uid,
                                 context->ipc.perm_gid,
                                 context->ipc.perm_mode);
-                        if (!ab)
-                                return;
                 }
                 break; }
         case AUDIT_MQ_OPEN: {
@@ -2720,6 +2720,8 @@ void audit_core_dumps(long signr)
                 return;
 
         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_ANOM_ABEND);
+        if (unlikely(!ab))
+                return;
         audit_log_abend(ab, "memory violation", signr);
         audit_log_end(ab);
 }