In the Linux kernel, the following vulnerability has been resolved: xfrm: fix compat ALLOCSPI request use-after-free xfrm_state_netlink()

In the Linux kernel, the following vulnerability has been resolved:

xfrm: fix compat ALLOCSPI request use-after-free

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.