Heap-based Buffer Overflow Affecting kernel-rt-kvm package, versions <0:3.10.0-693.5.2.rt56.626.el7

Note: Versions mentioned in the description apply only to the upstream kernel-rt-kvm package and not the kernel-rt-kvm package as distributed by Centos. See How to fix? for Centos:7 relevant fixed versions and status.

Linux kernel: Exploitable memory corruption due to UFO to non-UFO path switch. 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.

• http://www.securityfocus.com/bid/100262
• https://access.redhat.com/security/cve/CVE-2017-1000112
• http://www.debian.org/security/2017/dsa-3981
• https://www.exploit-db.com/exploits/45147/
• https://github.com/xairy/kernel-exploits/tree/master/CVE-2017-1000112
• http://seclists.org/oss-sec/2017/q3/277
• https://access.redhat.com/errata/RHSA-2017:2931
• http://www.securitytracker.com/id/1039162
• https://www.exploit-db.com/exploits/47169