CVE-2017-1000112

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.

Notes