From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59499) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WkNSx-0002RY-Lf for qemu-devel@nongnu.org; Tue, 13 May 2014 20:54:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WkNSq-0001hd-69 for qemu-devel@nongnu.org; Tue, 13 May 2014 20:54:39 -0400 Received: from mail-pb0-x233.google.com ([2607:f8b0:400e:c01::233]:42381) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WkNSp-0001hP-Qk for qemu-devel@nongnu.org; Tue, 13 May 2014 20:54:32 -0400 Received: by mail-pb0-f51.google.com with SMTP id ma3so920622pbc.24 for ; Tue, 13 May 2014 17:54:30 -0700 (PDT) Date: Wed, 14 May 2014 00:54:50 +0000 From: "Edgar E. Iglesias" Message-ID: <20140514005449.GC21821@hostname> References: <1396218189-14422-1-git-send-email-samuel.thibault@ens-lyon.org> <1396218189-14422-2-git-send-email-samuel.thibault@ens-lyon.org> <20140507221509.GA3302@type.youpi.perso.aquilenet.fr> <20140508061018.GB7523@hostname> <20140508065033.GT6261@type.youpi.perso.aquilenet.fr> <20140508065921.GH7381@hostname> <20140513221547.GE6302@type.youpi.perso.aquilenet.fr> <20140514003009.GB21821@hostname> <20140514004420.GV6302@type.youpi.perso.aquilenet.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20140514004420.GV6302@type.youpi.perso.aquilenet.fr> Subject: Re: [Qemu-devel] [PATCH, DoS] slirp (arp): do not special-case bogus IP addresses List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Samuel Thibault Cc: qemu-devel@nongnu.org On Wed, May 14, 2014 at 02:44:20AM +0200, Samuel Thibault wrote: > Edgar E. Iglesias, le Wed 14 May 2014 00:30:09 +0000, a écrit : > > > At best I could think of using the patch below, which avoids registering > > > anything for 0.0.0.0, and use a broadcast to answer a guest which > > > would have used 0.0.0.0 as a source for whatever reason. I don't find > > > anything else reasonable. What would be preferred? > > > > Specs are not super clear on this but rfc1700 says that 0.0.0.0 is a source only address. > > I agree. > > > What I was trying to suggest was a mix between your two versions. > > Removing the assert in table_search and avoid adding 0.0.0.0/32 to the cache > > in table_add. We might need to complement with something that drops datagrams > > destined to 0.0.0.0 in upper layers so we dont keep trying, not sure. > > Does something like that make sense? > > So that would be this. > > Samuel This looks good to me. Minor nit, the comment in if_encap should say "0.0.0.0 can not be a destination address..." Cheers, Edgar > > > 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 avoiding having 0.0.0.0 as a destination, however. > > Signed-off-by: Samuel Thibault > --- > > 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..2f189e0 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 can not be a source 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; > 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..2f189e0 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 can not a a source address, something went wrong, avoid > + * making it 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;