Re: [PATCH v2 net] net/ipv4: defensive cipso option parsing

From: Stefan Nuernberger <redacted>
Date: Mon, 17 Sep 2018 19:46:53 +0200

commit 40413955ee26 ("Cipso: cipso_v4_optptr enter infinite loop") fixed
a possible infinite loop in the IP option parsing of CIPSO. The fix
assumes that ip_options_compile filtered out all zero length options and
that no other one-byte options beside IPOPT_END and IPOPT_NOOP exist.
While this assumption currently holds true, add explicit checks for zero
length and invalid length options to be safe for the future. Even though
ip_options_compile should have validated the options, the introduction of
new one-byte options can still confuse this code without the additional
checks.

Signed-off-by: Stefan Nuernberger <redacted>

Applied to net-next.

This is not 'net' nor -stable material.  I'm hesitent about this
change as-is, and ip_options_compile() is not changing semantics in
-stable in the way that you say can cause problems.