Date: Tue, 31 Mar 2015 19:48:10 -0400 From: Rich Felker <dalias@...c.org> To: Denys Vlasenko <vda.linux@...glemail.com> Cc: busybox <busybox@...ybox.net>, musl <musl@...ts.openwall.com> Subject: Re: Busybox on musl is affected by CVE-2015-1817 On Tue, Mar 31, 2015 at 09:07:19PM +0200, Denys Vlasenko wrote: > On Mon, Mar 30, 2015 at 7:31 AM, Rich Felker <dalias@...c.org> wrote: > > For details on CVE-2015-1817, see: > > http://www.openwall.com/lists/musl/2015/03/30/1 > > > > With musl-linked Busybox installed setuid and ping enabled, exploiting > > this issue is trivial. > > > > While CVE-2015-1817 is certainly musl's fault, there are two changes > > to Busybox I'd like to propose that would have prevented it from being > > exploitable: > > > > 1. Having setuid utilities like ping obtain the resource they need (in > > the case of ping, SOCK_RAW) without processing user input at all, > > then fully dropping root (setuid(getuid())) before doing anything. > > This has been standard practice for setuid programs since the 90s > > and it feels bad that busybox is not doing it. > > In general this is acceptable, but with this particular case > and CVE, it wouldn't help. Sure it does. > create_icmp_socket(lsa) needs to know of which address family > the socket should be: > > if (lsa->u.sa.sa_family == AF_INET6) > sock = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6); > else > sock = socket(AF_INET, SOCK_RAW, 1); /* 1 == ICMP */ > > This is only known after HOST is parsed. > And CVE is in DNS resolving code :( The solution is simple: create both raw sockets and close the one you don't need later. There's probably also a way to use the AF_INET6 raw socket or IPv4 ping, but I don't know right off. > > 2. Reconsider the rejection of the patch to add SOCK_DGRAM support for > > ping, which allows it to run without root. > > This seems to lead to a significantly larger code. I don't recall the exact amount, but given that busybox's suid framework is not taking any precautions to mitigate the risks of suid (not to mention that eliminating all suids is a goal of some security-conscious systems integrators) I think it would be worth it even if it doubled the size of the ping utility (which it does not). Rich
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