On Wed, May 14, 2014 at 03:13:09AM +0200, Samuel Thibault wrote:
> Do not special-case addresses with zero host part, as we do not
> necessarily know how big it is, and the guest can fake them anyway.
> Silently avoid having 0.0.0.0 as a destination, however.
>
> Signed-off-by: Samuel Thibault <samuel.thiba...@ens-lyon.org>
I've pushed this to master, thanks.
Edgar
> ---
>
> This is particularly bad actually, one can for instance simply do this
> inside a Linux guest
>
> ip addr add 192.0.0.0/1 dev eth0
>
> and crash qemu (thus a DoS) by just emitting a packet (thus from
> 192.0.0.0), getting:
>
> qemu-system-x86_64: /usr/src/qemu/slirp/arp_table.c:77: arp_table_search:
> Assertion `(ip_addr & __bswap_32 (~(0xfU << 28))) != 0' failed.
>
> so it should probably go to all stable maintained versions.
>
> diff --git a/slirp/arp_table.c b/slirp/arp_table.c
> index ecdb0ba..bcaeb44 100644
> --- a/slirp/arp_table.c
> +++ b/slirp/arp_table.c
> @@ -37,12 +37,7 @@ void arp_table_add(Slirp *slirp, uint32_t ip_addr, uint8_t
> ethaddr[ETH_ALEN])
> ethaddr[0], ethaddr[1], ethaddr[2],
> ethaddr[3], ethaddr[4], ethaddr[5]));
>
> - /* Check 0.0.0.0/8 invalid source-only addresses */
> - if ((ip_addr & htonl(~(0xfU << 28))) == 0) {
> - return;
> - }
> -
> - if (ip_addr == 0xffffffff || ip_addr == broadcast_addr) {
> + if (ip_addr == 0 || ip_addr == 0xffffffff || ip_addr == broadcast_addr) {
> /* Do not register broadcast addresses */
> return;
> }
> @@ -73,9 +68,6 @@ bool arp_table_search(Slirp *slirp, uint32_t ip_addr,
> DEBUG_CALL("arp_table_search");
> DEBUG_ARG("ip = 0x%x", ip_addr);
>
> - /* Check 0.0.0.0/8 invalid source-only addresses */
> - assert((ip_addr & htonl(~(0xfU << 28))) != 0);
> -
> /* If broadcast address */
> if (ip_addr == 0xffffffff || ip_addr == broadcast_addr) {
> /* return Ethernet broadcast address */
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index 3fb48a4..00f4eb5 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -778,6 +778,11 @@ int if_encap(Slirp *slirp, struct mbuf *ifm)
> return 1;
> }
>
> + if (iph->ip_dst.s_addr == 0) {
> + /* 0.0.0.0 can not be a destination address, something went wrong,
> + * avoid making it worse */
> + return 1;
> + }
> if (!arp_table_search(slirp, iph->ip_dst.s_addr, ethaddr)) {
> uint8_t arp_req[ETH_HLEN + sizeof(struct arphdr)];
> struct ethhdr *reh = (struct ethhdr *)arp_req;
>
