Patch "fscrypt: 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

fscrypt: 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:
fscrypt-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 12:46:18 -0700
Subject: fscrypt: fix dereference of NULL user_key_payload

From: Eric Biggers <[email protected]>

commit d60b5b7854c3d135b869f74fb93eaf63cbb1991a upstream.

When an fscrypt-encrypted file is opened, we request the file's master key from the keyrings service as a logon key, then access its payload. However, a revoked key has a NULL payload, and we failed to check for this. 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.

---
 fs/ext4/crypto_key.c |    6 ++++++
 fs/f2fs/crypto_key.c |    6 ++++++
 2 files changed, 12 insertions(+)

@@ -204,6 +204,12 @@ int ext4_get_encryption_info(struct inod
 	}
 	down_read(&keyring_key->sem);
 	ukp = user_key_payload(keyring_key);
+	if (!ukp) {
+		/* key was revoked before we acquired its semaphore */
+		res = -EKEYREVOKED;
+		up_read(&keyring_key->sem);
+		goto out;
+	}
 	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 		res = -EINVAL;
 		up_read(&keyring_key->sem);

@@ -195,6 +195,12 @@ int f2fs_get_encryption_info(struct inod
 	}
 	down_read(&keyring_key->sem);
 	ukp = user_key_payload(keyring_key);
+	if (!ukp) {
+		/* key was revoked before we acquired its semaphore */
+		res = -EKEYREVOKED;
+		up_read(&keyring_key->sem);
+		goto out;
+	}
 	if (ukp->datalen != sizeof(struct f2fs_encryption_key)) {
 		res = -EINVAL;
 		up_read(&keyring_key->sem);

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

queue-4.4/keys-fix-race-between-updating-and-finding-a-negative-key.patch queue-4.4/fscrypto-require-write-access-to-mount-to-set-encryption-policy.patch queue-4.4/fs-cache-fix-dereference-of-null-user_key_payload.patch queue-4.4/lib-digsig-fix-dereference-of-null-user_key_payload.patch queue-4.4/fscrypt-fix-dereference-of-null-user_key_payload.patch queue-4.4/f2fs-crypto-add-missing-locking-for-keyring_key-access.patch queue-4.4/keys-encrypted-fix-dereference-of-null-user_key_payload.patch queue-4.4/f2fs-crypto-replace-some-bug_on-s-with-error-checks.patch queue-4.4/keys-don-t-let-add_key-update-an-uninstantiated-key.patch