cifs: check offset in decode_ntlmssp_challenge()

We should check that we're not copying memory from beyond the end of the
blob.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>

fs/cifs/sess.c

@@ -395,6 +395,10 @@ static int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
 	ses->ntlmssp->server_flags = le32_to_cpu(pblob->NegotiateFlags);
 	tioffset = le32_to_cpu(pblob->TargetInfoArray.BufferOffset);
 	tilen = le16_to_cpu(pblob->TargetInfoArray.Length);
+	if (tioffset > blob_len || tioffset + tilen > blob_len) {
+		cERROR(1, "tioffset + tilen too high %u + %u", tioffset, tilen);
+		return -EINVAL;
+	}
 	if (tilen) {
 		ses->auth_key.response = kmalloc(tilen, GFP_KERNEL);
 		if (!ses->auth_key.response) {