nbd/client: Add safety check on chunk payload length
Our existing use of structured replies either reads into a qiov capped
at 32M (NBD_CMD_READ) or caps allocation to 1000 bytes (see
NBD_MAX_MALLOC_PAYLOAD in block/nbd.c). But the existing length
checks are rather late; if we encounter a buggy (or malicious) server
that sends a super-large payload length, we should drop the connection
right then rather than assuming the layer on top will be careful.
This becomes more important when we permit 64-bit lengths which are
even more likely to have the potential for attempted denial of service
abuse.
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20230608135653.2918540-8-eblake@redhat.com>
diff --git a/nbd/client.c b/nbd/client.c
index ea3590c..1b55695 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -1413,6 +1413,18 @@
chunk->cookie = be64_to_cpu(chunk->cookie);
chunk->length = be32_to_cpu(chunk->length);
+ /*
+ * Because we use BLOCK_STATUS with REQ_ONE, and cap READ requests
+ * at 32M, no valid server should send us payload larger than
+ * this. Even if we stopped using REQ_ONE, sane servers will cap
+ * the number of extents they return for block status.
+ */
+ if (chunk->length > NBD_MAX_BUFFER_SIZE + sizeof(NBDStructuredReadData)) {
+ error_setg(errp, "server chunk %" PRIu32 " (%s) payload is too long",
+ chunk->type, nbd_rep_lookup(chunk->type));
+ return -EINVAL;
+ }
+
return 0;
}
