Patch "KEYS: encrypted: fix dereference of NULL user_key_payload" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

KEYS: encrypted: fix dereference of NULL user_key_payload

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
keys-encrypted-fix-dereference-of-null-user_key_payload.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Biggers <[email protected]>
Date: Mon, 9 Oct 2017 12:37:49 -0700
Subject: KEYS: encrypted: fix dereference of NULL user_key_payload

From: Eric Biggers <[email protected]>

commit 13923d0865ca96312197962522e88bc0aedccd74 upstream.

A key of type "encrypted" references a "master key" which is used to encrypt and decrypt the encrypted key's payload. However, when we accessed the master key's payload, we failed to handle the case where the master key has been revoked, which sets the payload pointer to NULL. Note that request_key() *does* skip revoked keys, but there is still a window where the key can be revoked before we acquire its semaphore.

Fix it by checking for a NULL payload, treating it like a key which was already revoked at the time it was requested.

This was an issue for master keys of type "user" only. Master keys can also be of type "trusted", but those cannot be revoked.

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

@@ -315,6 +315,13 @@ static struct key *request_user_key(cons
 
 	down_read(&ukey->sem);
 	upayload = user_key_payload(ukey);
+	if (!upayload) {
+		/* key was revoked before we acquired its semaphore */
+		up_read(&ukey->sem);
+		key_put(ukey);
+		ukey = ERR_PTR(-EKEYREVOKED);
+		goto error;
+	}
 	*master_key = upayload->data;
 	*master_keylen = upayload->datalen;
 error:

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/lib-digsig-fix-dereference-of-null-user_key_payload.patch queue-4.4/keys-encrypted-fix-dereference-of-null-user_key_payload.patch queue-4.4/keys-don-t-let-add_key-update-an-uninstantiated-key.patch