[PATCH net] cipso: adjust cached option offsets when removing CIPSO

[sashiko-bot at kernel.org]

> cipso_v4_skbuff_delattr() shifts every IPv4 option after CIPSO left by
> cipso_len, but leaves the cached srr, rr, ts and router_alert offsets at
> their old locations.
> 
> With a valid eight-byte CIPSO option followed by a seven-byte RR option,
> RR moves from offset 28 to 20 while opt->rr remains 28.  The stale offset
> then points into packet payload, letting the sender control both the
> length and bytes copied by __ip_options_echo().  Setting the length to
> 255 produced this condensed KASAN result:
> 
>   BUG: KASAN: stack-out-of-bounds in __ip_options_echo
>   Write of size 255
>   Call Trace:
>    __ip_options_echo
>    run_cipso_stale_offset [net_candidate_probe]
> [ ... ]
> 
> Fixes: 89aa3619d141 ("cipso: make cipso_v4_skbuff_delattr() fully remove the CIPSO options")
> Cc: stable at vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Daehyeon Ko <4ncienth at gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260930140400.2955466-1-4ncienth@gmail.com?part=1