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xfrm: ah: use skb_to_full_sk in async output callbacks

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When AH output is offloaded to an asynchronous crypto provider
(hardware accelerators such as AMD CCP, or a forced-async software
shim used for testing), the digest completion fires
ah_output_done() / ah6_output_done() on a workqueue.  The egress
skb at that point may have been originated by a TCP listener
sending a SYN-ACK, which sets skb->sk to a request_sock via
skb_set_owner_edemux(); it may also have been originated by an
inet_timewait_sock retransmit.  Neither is a full struct sock, and
passing the raw skb->sk to xfrm_output_resume() then forwards a
non-full socket through the rest of the xfrm output chain.

xfrm_output_resume() and its downstream consumers expect a full
sk where they dereference at all.  The natural egress path
through ah_output_done() does not crash today because the
consumers that read past sock_common are either gated by
sk_fullsock() or short-circuit on flags that are clear on a fresh
request_sock; an exhaustive walk of the 50 most plausible
consumers under sch_fq, dev_queue_xmit, netfilter, tc-egress and
cgroup-egress BPF found no current unguarded deref.  The bug is
still a real type confusion that future consumer changes could
turn into a memory-corruption primitive.

This is the same bug class fixed for ESP in commit 1620c88887
("xfrm: Fix the usage of skb->sk").  Apply the analogous fix to
AH: convert skb->sk to a full socket pointer (or NULL) via
skb_to_full_sk() before handing it to xfrm_output_resume().

The same async AH callbacks were touched recently for an
independent ESN-related ICV layout bug in commit ec54093e6a
("xfrm: ah: account for ESN high bits in async callbacks"); the
sk type-confusion addressed here is orthogonal.  This patch is
part of an ongoing audit of the AH callback paths; an ah_output
ihl-validation hardening series is also currently under review on
netdev.

Reproduced under UML + KASAN + lockdep with a forced-async
hmac(sha1) shim that registers at priority 9999 and wraps the
sync in-tree hmac-sha1-lib.  With the shim loaded, ah_output_done
runs on every SYN-ACK egress through a transport-mode AH SA and
skb->sk arrives as a request_sock (TCP_NEW_SYN_RECV); after this
patch, xfrm_output_resume() receives the listener (the result of
sk_to_full_sk()) and consumer derefs land on full-sock fields as
intended.

Fixes: 9ab1265d52 ("xfrm: Use actual socket sk instead of skb socket for xfrm_output_resume")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
This commit is contained in:
Michael Bommarito 2026-05-15 11:45:31 -04:00 committed by Steffen Klassert
parent 742b04d055
commit 79d8be2623
2 changed files with 2 additions and 2 deletions
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2
net/ipv4/ah4.c
View File

@ -143,7 +143,7 @@ static void ah_output_done(void *data, int err)
}
kfree(AH_SKB_CB(skb)->tmp);
xfrm_output_resume(skb->sk, skb, err);
xfrm_output_resume(skb_to_full_sk(skb), skb, err);
}
static int ah_output(struct xfrm_state *x, struct sk_buff *skb)

2
net/ipv6/ah6.c
View File

@ -337,7 +337,7 @@ static void ah6_output_done(void *data, int err)
ah6_restore_hdrs(top_iph, iph_ext, extlen);
kfree(AH_SKB_CB(skb)->tmp);
xfrm_output_resume(skb->sk, skb, err);
xfrm_output_resume(skb_to_full_sk(skb), skb, err);
}
static int ah6_output(struct xfrm_state *x, struct sk_buff *skb)