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Message-ID: <20141106221608.GA7996@ZenIV.linux.org.uk> Date: Thu, 6 Nov 2014 22:16:08 +0000 From: Al Viro <viro@...IV.linux.org.uk> To: Jon Maloy <jon.maloy@...csson.com> Cc: Herbert Xu <herbert@...dor.apana.org.au>, David Miller <davem@...emloft.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "bcrl@...ck.org" <bcrl@...ck.org>, Masahide Nakamura <nakam@...ux-ipv6.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org> Subject: Re: ipv4: Use standard iovec primitive in raw_probe_proto_opt On Thu, Nov 06, 2014 at 09:55:31AM +0000, Jon Maloy wrote: > > Point, but that might very well be a pattern to watch for - there's at least one > > more instance in TIPC (also not exploitable, according to TIPC folks) and such > > I don't recall this, and I can't see where it would be either. Can you please > point to where it is? The same dest_name_check() thing. This if (copy_from_user(&hdr, m->msg_iov[0].iov_base, sizeof(hdr))) return -EFAULT; if ((ntohs(hdr.tcm_type) & 0xC000) && (!capable(CAP_NET_ADMIN))) return -EACCES; is easily bypassed. Suppose you want to send a packet with these two bits in ->tcm_type not being 00, and you don't have CAP_NET_ADMIN. Not a problem - spawn two threads sharing memory, have one trying to call sendmsg() while another keeps flipping these two bits. Sooner of later you'll get the timing right and have these bits observed as 00 in dest_name_check() and 11 when it comes to memcpy_fromiovecend() actually copying the whole thing. And considering that the interval between those two is much longer than the loop in the second thread would take on each iteration, I'd expect the odds around 25% per attempted sendmsg(). IOW, this test is either pointless and can be removed completely, or there's an exploitable race. As far as I understand from your replies both back then and in another branch of this thread, it's the former and the proper fix is to remove at least that part of dest_name_check(). So this case is also not something exploitable, but it certainly matches the same pattern. My point was simply that this pattern is worth watching for - recurrent bug classes like that have a good chance to spawn an instance that will be exploitable. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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