4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Biggers <ebiggers@xxxxxxxxxx> commit 192cabd6a296cbc57b3d8c05c4c89d87fc102506 upstream. 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: 051dbb918c7f ("crypto: digital signature verification support") Reviewed-by: James Morris <james.l.morris@xxxxxxxxxx> Cc: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: David Howells <dhowells@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- lib/digsig.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/lib/digsig.c +++ b/lib/digsig.c @@ -87,6 +87,12 @@ static int digsig_verify_rsa(struct key down_read(&key->sem); ukp = user_key_payload(key); + if (!ukp) { + /* key was revoked before we acquired its semaphore */ + err = -EKEYREVOKED; + goto err1; + } + if (ukp->datalen < sizeof(*pkh)) goto err1;