[PATCH] NETWORKING: avoid use IPCB in cipso_v4_error

[David Miller]

From: Nazarov Sergey <s-nazarov at yandex.ru>
Date: Tue, 12 Feb 2019 18:10:03 +0300

> Since cipso_v4_error might be called from different network stack layers, we can't safely use icmp_send there.
> icmp_send copies IP options with ip_option_echo, which uses IPCB to take access to IP header compiled data.
> But after commit 971f10ec ("tcp: better TCP_SKB_CB layout to reduce cache line misses"), IPCB can't be used
> above IP layer.
> This patch fixes the problem by creating in cipso_v4_error a local copy of compiled IP options and using it with
> introduced __icmp_send function. This looks some overloaded, but in quite rare error conditions only.
> 
> The original discussion is here:
> https://lore.kernel.org/linux-security-module/16659801547571984@sas1-890ba5c2334a.qloud-c.yandex.net/
> 
> Signed-off-by: Sergey Nazarov <s-nazarov at yandex.ru>

This problem is not unique to Cipso, net/atm/clip.c's error handler
has the same exact issue.

I didn't scan more of the tree, there are probably a couple more
locations as well.