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xfrm: fix compat ALLOCSPI request use-after-free

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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: 5f3eea6b7e ("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@openai.com>
Co-developed-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
This commit is contained in:
Kyle Zeng 2026-08-04 06:10:37 +00:00 committed by Steffen Klassert
parent 6973a21ee7
commit d1ebd90818
1 changed files with 0 additions and 12 deletions
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12
net/xfrm/xfrm_user.c
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@ -1877,7 +1877,6 @@ static int xfrm_alloc_userspi(struct sk_buff *skb, struct nlmsghdr *nlh,
struct net *net = sock_net(skb->sk);
struct xfrm_state *x;
struct xfrm_userspi_info *p;
struct xfrm_translator *xtr;
struct sk_buff *resp_skb;
xfrm_address_t *daddr;
int family;
@ -1943,17 +1942,6 @@ static int xfrm_alloc_userspi(struct sk_buff *skb, struct nlmsghdr *nlh,
goto out;
}
xtr = xfrm_get_translator();
if (xtr) {
err = xtr->alloc_compat(skb, nlmsg_hdr(skb));
xfrm_put_translator(xtr);
if (err) {
kfree_skb(resp_skb);
goto out;
}
}
err = nlmsg_unicast(xfrm_net_nlsk(net, skb), resp_skb, NETLINK_CB(skb).portid);
out: