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From c4ea553123a5ab1bf5fab38f12a540020c08293d Mon Sep 17 00:00:00 2001
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From: David Lamparter <equinox@opensourcerouting.org>
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Date: Wed, 31 Aug 2016 13:31:16 +0200
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Subject: [PATCH 4/4] zebra: stack overrun in IPv6 RA receive code
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(CVE-2016-1245)
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The IPv6 RA code also receives ICMPv6 RS and RA messages.
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Unfortunately, by bad coding practice, the buffer size specified on
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receiving such messages mixed up 2 constants that in fact have
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different values.
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The code itself has:
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#define RTADV_MSG_SIZE 4096
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While BUFSIZ is system-dependent, in my case (x86_64 glibc):
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/usr/include/_G_config.h:#define _G_BUFSIZ 8192
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/usr/include/libio.h:#define _IO_BUFSIZ _G_BUFSIZ
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/usr/include/stdio.h:# define BUFSIZ _IO_BUFSIZ
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FreeBSD, OpenBSD, NetBSD and Illumos are not affected, since all of them
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have BUFSIZ == 1024.
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As the latter is passed to the kernel on recvmsg(), it's possible to
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overwrite 4kB of stack -- with ICMPv6 packets that can be globally sent
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to any of the system's addresses (using fragmentation to get to 8k).
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(The socket has filters installed limiting this to RS and RA packets,
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but does not have a filter for source address or TTL.)
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Issue discovered by trying to test other stuff, which randomly caused
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the stack to be smaller than 8kB in that code location, which then
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causes the kernel to report EFAULT (Bad address).
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Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
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Reviewed-by: Donald Sharp <sharpd@cumulusnetworks.com>
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Cherry-picked from: cfb1fae25f8c092e0d17073eaf7bd428ce1cd546
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Resolves: #1386110
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---
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zebra/rtadv.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/zebra/rtadv.c b/zebra/rtadv.c
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index 21ca6da..973ae08 100644
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--- a/zebra/rtadv.c
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+++ b/zebra/rtadv.c
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@@ -515,7 +515,7 @@ rtadv_read (struct thread *thread)
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/* Register myself. */
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rtadv_event (RTADV_READ, sock);
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- len = rtadv_recv_packet (sock, buf, BUFSIZ, &from, &ifindex, &hoplimit);
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+ len = rtadv_recv_packet (sock, buf, sizeof (buf), &from, &ifindex, &hoplimit);
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if (len < 0)
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{
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--
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2.7.4
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