selinux: fix a missing-check bug in selinux_add_mnt_opt( )

In selinux_add_mnt_opt(), 'val' is allocated by kmemdup_nul(). It returns
NULL when fails. So 'val' should be checked. And 'mnt_opts' should be
freed when error.
Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
Fixes: 757cbe59 ("LSM: new method: ->sb_add_mnt_opt()")
Cc: <stable@vger.kernel.org>
[PM: fixed some indenting problems]
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -1052,15 +1052,24 @@ static int selinux_add_mnt_opt(const char *option, const char *val, int len,
 	if (token == Opt_error)
 		return -EINVAL;
 
-	if (token != Opt_seclabel)
+	if (token != Opt_seclabel) {
 		val = kmemdup_nul(val, len, GFP_KERNEL);
+		if (!val) {
+			rc = -ENOMEM;
+			goto free_opt;
+		}
+	}
 	rc = selinux_add_opt(token, val, mnt_opts);
 	if (unlikely(rc)) {
 		kfree(val);
-		if (*mnt_opts) {
-			selinux_free_mnt_opts(*mnt_opts);
-			*mnt_opts = NULL;
-		}
+		goto free_opt;
+	}
+	return rc;
+
+free_opt:
+	if (*mnt_opts) {
+		selinux_free_mnt_opts(*mnt_opts);
+		*mnt_opts = NULL;
 	}
 	return rc;
 }