[PATCH 4.9 34/51] LSM: Check for NULL cred-security on free

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

From: James Morris <james.morris@microsoft.com>

commit a5795fd38ee8194451ba3f281f075301a3696ce2 upstream.

From: Casey Schaufler <casey@schaufler-ca.com>

Check that the cred security blob has been set before trying
to clean it up. There is a case during credential initialization
that could result in this.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <james.morris@microsoft.com>
Reported-by: syzbot+69ca07954461f189e808@syzkaller.appspotmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 security/security.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/security/security.c
+++ b/security/security.c
@@ -904,6 +904,13 @@ int security_cred_alloc_blank(struct cre
 
 void security_cred_free(struct cred *cred)
 {
+	/*
+	 * There is a failure case in prepare_creds() that
+	 * may result in a call here with ->security being NULL.
+	 */
+	if (unlikely(cred->security == NULL))
+		return;
+
 	call_void_hook(cred_free, cred);
 }