Re: [Qemu-devel] [PATCH v2] slirp: udp: fix NULL pointer dereference because of uninitialized socket

[Michael Tokarev]

18.09.2014 10:35, Petr Matousek wrote:
> When guest sends udp packet with source port and source addr 0,
> uninitialized socket is picked up when looking for matching and already
> created udp sockets, and later passed to sosendto() where NULL pointer
> dereference is hit during so->slirp->vnetwork_mask.s_addr access.
> 
> Fix this by checking that the socket is not just a socket stub.
> 
> This is CVE-2014-3640.
> 
> Signed-off-by: Petr Matousek <address@hidden>
> Reported-by: Xavier Mehrenberger <address@hidden>
> Reported-by: Stephane Duverger <address@hidden>

Reviewed-by: Michael Tokarev <address@hidden>

slirp->udb initially is a dummy element of the list which initially
points to itself and never gets used (and slirp->udp_last_so initially
points to it too).

Thanks,

/mjt

>  slirp/udp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/slirp/udp.c b/slirp/udp.c
> index 8cc6cb6..f77e00f 100644
> --- a/slirp/udp.c
> +++ b/slirp/udp.c
> @@ -152,7 +152,7 @@ udp_input(register struct mbuf *m, int iphlen)
>        * Locate pcb for datagram.
>        */
>       so = slirp->udp_last_so;
> -     if (so->so_lport != uh->uh_sport ||
> +     if (so == &slirp->udb || so->so_lport != uh->uh_sport ||
>           so->so_laddr.s_addr != ip->ip_src.s_addr) {
>               struct socket *tmp;
>  
>