fscrypt: fix dereference of NULL user_key_payload

commit d60b5b7854 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.

Fixes: 88bd6ccdcd ("ext4 crypto: add encryption key management facilities")
Reviewed-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
master
Eric Biggers 6 years ago committed by Greg Kroah-Hartman
parent f374505b79
commit b2ac5d4516

@ -108,6 +108,11 @@ static int validate_user_key(struct fscrypt_info *crypt_info,
goto out;
}
ukp = user_key_payload(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/* key was revoked before we acquired its semaphore */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;

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