[PATCH 4.4 078/117] ext4 crypto: add missing locking for keyring_key access

[Greg Kroah-Hartman]

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

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

From: Theodore Ts'o <tytso@xxxxxxx>

commit db7730e3091a52c2fcd8fcc952b964d88998e675 upstream.

Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/ext4/crypto_key.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/ext4/crypto_key.c
+++ b/fs/ext4/crypto_key.c
@@ -213,9 +213,11 @@ retry:
 		res = -ENOKEY;
 		goto out;
 	}
+	down_read(&keyring_key->sem);
 	ukp = user_key_payload(keyring_key);
 	if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
 		res = -EINVAL;
+		up_read(&keyring_key->sem);
 		goto out;
 	}
 	master_key = (struct ext4_encryption_key *)ukp->data;
@@ -226,10 +228,12 @@ retry:
 			    "ext4: key size incorrect: %d\n",
 			    master_key->size);
 		res = -ENOKEY;
+		up_read(&keyring_key->sem);
 		goto out;
 	}
 	res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
 				  raw_key);
+	up_read(&keyring_key->sem);
 	if (res)
 		goto out;
 got_key: