LSM: Check for NULL cred-security on free

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

1 files changed, 7 insertions, 0 deletions

diff --git a/security/security.c b/security/security.c
index f1b8d2587639..55bc49027ba9 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1027,6 +1027,13 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
 
 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);
 }