Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date: Thu, 10 Aug 2017 22:55:29 +0200
From: Andrey Konovalov <>
Cc:, Dmitry Vyukov <>, 
	Kostya Serebryany <>
Subject: Linux kernel: CVE-2017-1000112: Exploitable memory corruption due to
 UFO to non-UFO path switch


syzkaller found an exploitable memory corruption in UFO code in the
Linux kernel, the details are below.

### Bug details

When building a UFO packet with MSG_MORE __ip_append_data() calls
ip_ufo_append_data() to append. However in between two send() calls,
the append path can be switched from UFO to non-UFO one, which leads
to a memory corruption.

In case UFO packet lengths exceeds MTU, copy = maxfraglen - skb->len
becomes negative on the non-UFO path and the branch to allocate new
skb is taken. This triggers fragmentation and computation of fraggap =
skb_prev->len - maxfraglen. Fraggap can exceed MTU, causing copy =
datalen - transhdrlen - fraggap to become negative. Subsequently
skb_copy_and_csum_bits() writes out-of-bounds.

A similar issue is present in IPv6 code.

The bug was introduced in e89e9cf539a2 ("[IPv4/IPv6]: UFO
Scatter-gather approach") on Oct 18 2005.

The fix has been submitted to netdev [1] and should be committed to
mainline and to stable kernels soon. David has also sent an RFC series
to remove UFO completely [2], which should be merged in 4.14.

If unprivileged user namespaces are available, this bug can be
exploited to gain root privileges. I'll share the details and the
exploit in a few days.


### Timeline

2017.08.03 - Bug reported to
2017.08.04 - Bug reported to linux-distros@
2017.08.10 - Patch submitted to netdev
2017.08.10 - Announcement on oss-security@

### Links



Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.