[PATCH] xfrm: ah: account for ESN high bits in async callbacks

[Michael Bommarito <michael.bommarito@gmail.com>]

AH allocates its temporary auth/ICV layout differently when ESN is enabled:
the async ahash setup appends a 4-byte seqhi slot before the ICV or
auth_data area, but the async completion callbacks still reconstruct the
temporary layout as if seqhi were absent.

With an async AH implementation selected, that makes AH copy or compare
the wrong bytes on both the IPv4 and IPv6 paths. In UML repro on IPv4 AH
with ESN and forced async hmac(sha1), ping fails with 100% packet loss,
and the callback logs show the pre-fix drift:

  ah4 output_done: esn=1 err=0 icv_off=20 expected_off=24
  ah4 input_done: esn=1 auth_off=20 expected_auth_off=24 icv_off=32 expected_icv_off=36

Reconstruct the callback-side layout the same way the setup path built it
by skipping the ESN seqhi slot before locating the saved auth_data or ICV.
Per RFC 4302, the ESN high-order 32 bits participate in the AH ICV
computation, so the async callbacks must account for the seqhi slot.

Post-fix, the same IPv4 AH+ESN+forced-async-hmac(sha1) UML repro shows
the corrected offset (ah4 output_done: esn=1 err=0 icv_off=24
expected_off=24) and ping succeeds; net/ipv4/ah4.o and net/ipv6/ah6.o
build clean at W=1. IPv6 AH+ESN was not exercised at runtime, and the
change has not been tested against a real async hardware AH engine.

Fixes: d4d573d0334d ("{IPv4,xfrm} Add ESN support for AH egress part")
Fixes: d8b2a8600b0e ("{IPv4,xfrm} Add ESN support for AH ingress part")
Fixes: 26dd70c3fad3 ("{IPv6,xfrm} Add ESN support for AH egress part")
Fixes: 8d6da6f32557 ("{IPv6,xfrm} Add ESN support for AH ingress part")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5-4
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 net/ipv4/ah4.c | 14 ++++++++++++--
 net/ipv6/ah6.c | 14 ++++++++++++--
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
index 5fb812443a08..4366cbac3f06 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -124,9 +124,14 @@ static void ah_output_done(void *data, int err)
 	struct iphdr *top_iph = ip_hdr(skb);
 	struct ip_auth_hdr *ah = ip_auth_hdr(skb);
 	int ihl = ip_hdrlen(skb);
+	int seqhi_len = 0;
+	__be32 *seqhi;
 
+	if (x->props.flags & XFRM_STATE_ESN)
+		seqhi_len = sizeof(*seqhi);
 	iph = AH_SKB_CB(skb)->tmp;
-	icv = ah_tmp_icv(iph, ihl);
+	seqhi = (__be32 *)((char *)iph + ihl);
+	icv = ah_tmp_icv(seqhi, seqhi_len);
 	memcpy(ah->auth_data, icv, ahp->icv_trunc_len);
 
 	top_iph->tos = iph->tos;
@@ -270,12 +275,17 @@ static void ah_input_done(void *data, int err)
 	struct ip_auth_hdr *ah = ip_auth_hdr(skb);
 	int ihl = ip_hdrlen(skb);
 	int ah_hlen = (ah->hdrlen + 2) << 2;
+	int seqhi_len = 0;
+	__be32 *seqhi;
 
 	if (err)
 		goto out;
 
+	if (x->props.flags & XFRM_STATE_ESN)
+		seqhi_len = sizeof(*seqhi);
 	work_iph = AH_SKB_CB(skb)->tmp;
-	auth_data = ah_tmp_auth(work_iph, ihl);
+	seqhi = (__be32 *)((char *)work_iph + ihl);
+	auth_data = ah_tmp_auth(seqhi, seqhi_len);
 	icv = ah_tmp_icv(auth_data, ahp->icv_trunc_len);
 
 	err = crypto_memneq(icv, auth_data, ahp->icv_trunc_len) ? -EBADMSG : 0;
diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index cb26beea4398..de1e68199a01 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -317,14 +317,19 @@ static void ah6_output_done(void *data, int err)
 	struct ipv6hdr *top_iph = ipv6_hdr(skb);
 	struct ip_auth_hdr *ah = ip_auth_hdr(skb);
 	struct tmp_ext *iph_ext;
+	int seqhi_len = 0;
+	__be32 *seqhi;
 
 	extlen = skb_network_header_len(skb) - sizeof(struct ipv6hdr);
 	if (extlen)
 		extlen += sizeof(*iph_ext);
 
+	if (x->props.flags & XFRM_STATE_ESN)
+		seqhi_len = sizeof(*seqhi);
 	iph_base = AH_SKB_CB(skb)->tmp;
 	iph_ext = ah_tmp_ext(iph_base);
-	icv = ah_tmp_icv(iph_ext, extlen);
+	seqhi = (__be32 *)((char *)iph_ext + extlen);
+	icv = ah_tmp_icv(seqhi, seqhi_len);
 
 	memcpy(ah->auth_data, icv, ahp->icv_trunc_len);
 	memcpy(top_iph, iph_base, IPV6HDR_BASELEN);
@@ -471,13 +476,18 @@ static void ah6_input_done(void *data, int err)
 	struct ip_auth_hdr *ah = ip_auth_hdr(skb);
 	int hdr_len = skb_network_header_len(skb);
 	int ah_hlen = ipv6_authlen(ah);
+	int seqhi_len = 0;
+	__be32 *seqhi;
 
 	if (err)
 		goto out;
 
+	if (x->props.flags & XFRM_STATE_ESN)
+		seqhi_len = sizeof(*seqhi);
 	work_iph = AH_SKB_CB(skb)->tmp;
 	auth_data = ah_tmp_auth(work_iph, hdr_len);
-	icv = ah_tmp_icv(auth_data, ahp->icv_trunc_len);
+	seqhi = (__be32 *)(auth_data + ahp->icv_trunc_len);
+	icv = ah_tmp_icv(seqhi, seqhi_len);
 
 	err = crypto_memneq(icv, auth_data, ahp->icv_trunc_len) ? -EBADMSG : 0;
 	if (err)
-- 
2.53.0