From 198ad1ea078c1b74c9e24617c509c6a408eb822e Mon Sep 17 00:00:00 2001 From: Frediano Ziglio Date: Mon, 28 Nov 2016 13:15:58 +0000 Subject: [PATCH] Prevent possible DoS attempts during protocol handshake The limit for link message is specified using a 32 bit unsigned integer. This could cause possible DoS due to excessive memory allocations and some possible crashes. For instance a value >= 2^31 causes a spice_assert to be triggered in async_read_handler (reds-stream.c) due to an integer overflow at this line: int n = async->end - async->now; This could be easily triggered with a program like #!/usr/bin/env python import socket import time from struct import pack server = '127.0.0.1' port = 5900 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((server, port)) data = pack('<4sIII', 'REDQ', 2, 2, 0xaaaaaaaa) s.send(data) time.sleep(1) without requiring any authentication (the same can be done with TLS). Signed-off-by: Frediano Ziglio --- server/reds.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/server/reds.c b/server/reds.c index 9e1d5e7..1c215ed 100644 --- a/server/reds.c +++ b/server/reds.c @@ -2826,7 +2826,8 @@ static void reds_handle_read_header_done(void *opaque) reds->peer_minor_version = header->minor_version; - if (header->size < sizeof(SpiceLinkMess)) { + /* the check for 4096 is to avoid clients to cause arbitrary big memory allocations */ + if (header->size < sizeof(SpiceLinkMess) || header->size > 4096) { reds_send_link_error(link, SPICE_LINK_ERR_INVALID_DATA); spice_warning("bad size %u", header->size); reds_link_free(link); -- 2.9.3