Re: [PATCH ipsec v2] xfrm: fix compat ALLOCSPI request use-after-free

[Steffen Klassert]

On Tue, Aug 04, 2026 at 06:10:37AM +0000, David Lee wrote:
> From: Kyle Zeng <kylebot@xxxxxxxxxx>
> 
> xfrm_state_netlink() builds the ALLOCSPI response with
> dump_one_state(), which already calls alloc_compat() with the response
> skb and header.
> 
> xfrm_alloc_userspi() then calls alloc_compat() again, but passes the
> original request skb and its header. For a compat request, the
> translator therefore interprets the 228-byte compat xfrm_userspi_info
> as the 232-byte native layout and reads four bytes past the declared
> payload. It also publishes the translated child through the request's
> frag_list.
> 
> A multicast clone of the request shares skb_shared_info and can observe
> that child. xfrm_user_rcv_msg() frees it after the request handler
> returns, racing a compat receiver which may still be copying from it and
> resulting in a use-after-free.
> 
> Remove the redundant conversion. The response keeps its correct compat
> translation from dump_one_state(), and no child is attached to the
> inbound request.
> 
> Fixes: 5f3eea6b7e8f ("xfrm/compat: Attach xfrm dumps to 64=>32 bit translator")
> Assisted-by: Codex:gpt-5.6-sol Codex:gpt-5.5-cyber
> Signed-off-by: Kyle Zeng <kylebot@xxxxxxxxxx>
> Co-developed-by: David Lee <david.lee@xxxxxxxxxxxxxxx>
> Signed-off-by: David Lee <david.lee@xxxxxxxxxxxxxxx>

Applied, thanks a lot!