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lib/digsig: fix dereference of NULL user_key_payload

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digsig_verify() requests a user key, then accesses 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: 051dbb918c ("crypto: digital signature verification support")
Reviewed-by: James Morris <james.l.morris@oracle.com>
Cc: <stable@vger.kernel.org>    [v3.3+]
Cc: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
Eric Biggers 2017-10-09 12:43:20 -07:00 committed by David Howells
parent d124b2c53c
commit 192cabd6a2
1 changed files with 6 additions and 0 deletions
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6
lib/digsig.c
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@ -87,6 +87,12 @@ static int digsig_verify_rsa(struct key *key,
down_read(&key->sem);
ukp = user_key_payload_locked(key);
if (!ukp) {
/* key was revoked before we acquired its semaphore */
err = -EKEYREVOKED;
goto err1;
}
if (ukp->datalen < sizeof(*pkh))
goto err1;