From 70fa99f445a6fabe4b46f188cc665cd469cd8293 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 8 Jun 2023 08:56:36 -0500 Subject: [PATCH] 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 Reviewed-by: Vladimir Sementsov-Ogievskiy Message-ID: <20230608135653.2918540-8-eblake@redhat.com> --- nbd/client.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/nbd/client.c b/nbd/client.c index ea3590ca3d..1b5569556f 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -1413,6 +1413,18 @@ static int nbd_receive_structured_reply_chunk(QIOChannel *ioc, 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; } -- 2.11.0