Re: [PATCH net v2] cipso: adjust cached option offsets when removing CIPSO

[Paul Moore]

On Mon, Oct 5, 2026 at 11:51 PM Daehyeon Ko <4ncienth@xxxxxxxxx> wrote:
>
> cipso_v4_skbuff_delattr() removes the CIPSO bytes but does not adjust
> cached offsets for options that follow them.
>
> For example, with a valid 10-byte CIPSO option followed by a seven-byte
> RR option, parsing records rr at offset 30.  Removing CIPSO moves RR to
> offset 20, while the cached offset remains 30.  Consumers such as
> ip_forward_options() and __ip_options_echo() then access the wrong bytes;
> the latter may interpret packet data as the option length and copy it into
> fixed-size option storage.
>
> Mirror cipso_v4_delopt() and subtract cipso_len from the srr, rr, ts and
> router_alert offsets when they follow CIPSO.  cipso_len is the distance
> the first memmove() shifts those options.  The later header move and
> network-header reset relocate the bytes and their offset base together.
>
> Fixes: 89aa3619d141 ("cipso: make cipso_v4_skbuff_delattr() fully remove the CIPSO options")
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Ondrej Mosnáček <omosnacek@xxxxxxxxx>
> Assisted-by: LLM
> Signed-off-by: Daehyeon Ko <4ncienth@xxxxxxxxx>
> ---
> Changes in v2:
> - Replace the parser-invalid 8-byte example with a valid 10-byte one.
> - Move the offset updates beside the other option metadata updates.
>
> Link: https://lore.kernel.org/netdev/20260930140400.2955466-1-4ncienth@xxxxxxxxx/
>
>  net/ipv4/cipso_ipv4.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>

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