lib/digsig: fix dereference of NULL user_key_payload
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@oracle.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin@intel.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>
diff --git a/lib/digsig.c b/lib/digsig.c
index ae05ea39..4b8ef0b 100644
--- a/lib/digsig.c
+++ b/lib/digsig.c
@@ -86,6 +86,12 @@
down_read(&key->sem);
ukp = key->payload.data;
+ if (!ukp) {
+ /* key was revoked before we acquired its semaphore */
+ err = -EKEYREVOKED;
+ goto err1;
+ }
+
if (ukp->datalen < sizeof(*pkh))
goto err1;