Re: [PATCH net 2/2] cipso: unshare headers before recompiling IP options in cipso_v4_error()

[sashiko-bot@kernel.org]

> cipso_v4_error() recompiles the IP options of the offending packet with
> __ip_options_compile() before echoing them in an ICMP error.
> __ip_options_compile() updates Record Route and Timestamp options in
> place.
> 
> cipso_v4_error() is called from the LSM socket receive hooks through
> netlbl_skbuff_err(). ip_rcv_options() unshared the IPv4 header earlier,
> but at socket delivery time the skb can again be a clone sharing its
> data with other skbs, such as the per-socket clones made for raw sockets
> or multicast/broadcast delivery. Writing to the options then modifies
> packet data seen by the other users of the buffer, and a concurrent
> recompilation would hit the same check-then-write race as the one fixed
> in ipv4_send_dest_unreach().
> 
> Make the header private before recompiling options, as ip_rcv_options()
> already does. If the copy fails, do not send the ICMP error.
> 
> Fixes: 3da1ed7ac398 ("net: avoid use IPCB in cipso_v4_error")
> Reported-by: Kyle Zeng <kylebot@openai.com>
> Cc: Paul Moore <paul@paul-moore.com>
> Cc: linux-security-module@vger.kernel.org
> Signed-off-by: Eric Dumazet <edumazet@kernel.org>

Sashiko has reviewed this patch and found no issues.

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