CVS: cvs.openbsd.org: src

CVSROOT:	/cvs
Module name:	src
Changes by:	[email protected]	2026/07/06 23:39:05

Modified files:
	sys/net        : pipex.c 

Log message:
don't assume an ipv4 header is always 20 bytes.

as reported by SecBuddyF, Tencent KeenLab:

> OpenBSD's pipex PPTP GRE packet handling uses a fixed GRE/IP header
> length check before later reading the GRE header at an offset derived
> from the actual IPv4 header length.
>
> When IPv4 options are present, the dynamic IPv4 header length can
> be larger than 20 bytes. A short GRE packet can therefore pass the
> fixed 28-byte PIPEX_IPGRE_HDRLEN check while still being too short
> for the later m_copydata(m0, hlen, sizeof(gre), &gre) read.
>
> This can trigger:
>
>   panic: m_copydata: null mbuf
>
> The issue is remotely triggerable when GRE and pipex are enabled
> and inbound IPv4 GRE packets with IP options are allowed to reach
> the target.

they identified the problem in pipex_pptp_lookup_session() and
suggested a minimal fix, but i reimplemented it to make it more
like other code in the tree. also, there were similar issues in
pipex_pptp_input() which i'm also fixing while here.

testing and ok yasuoak@