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[4/7] fscrypt: fix dereference of NULL user_key_payload

Message ID 20170928212602.41744-5-ebiggers3@gmail.com (mailing list archive)
State Accepted
Headers show

Commit Message

Eric Biggers Sept. 28, 2017, 9:25 p.m. UTC 
From: Eric Biggers <ebiggers@google.com>

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.

Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
Cc: <stable@vger.kernel.org>    [v4.1+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/crypto/keyinfo.c | 5 +++++
 1 file changed, 5 insertions(+)

Comments

James Morris Oct. 3, 2017, 10:56 a.m. UTC | #1 
On Thu, 28 Sep 2017, Eric Biggers wrote:

> From: Eric Biggers <ebiggers@google.com>
> 
> 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.
> 
> Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
> Cc: <stable@vger.kernel.org>    [v4.1+]
> Signed-off-by: Eric Biggers <ebiggers@google.com>


Reviewed-by: James Morris <james.l.morris@oracle.com>
diff mbox

Patch

diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c
index 018c588c7ac3..8e704d12a1cf 100644
--- a/fs/crypto/keyinfo.c
+++ b/fs/crypto/keyinfo.c
@@ -109,6 +109,11 @@  static int validate_user_key(struct fscrypt_info *crypt_info,
 		goto out;
 	}
 	ukp = user_key_payload_locked(keyring_key);
+	if (!ukp) {
+		/* key was revoked before we acquired its semaphore */
+		res = -EKEYREVOKED;
+		goto out;
+	}
 	if (ukp->datalen != sizeof(struct fscrypt_key)) {
 		res = -EINVAL;
 		goto out;