* [PATCH 6.12.y] tcp: fix potential race in tcp_v6_syn_recv_sock()
@ 2026-09-08 8:19 Michael Pfeifroth
0 siblings, 0 replies; only message in thread
From: Michael Pfeifroth @ 2026-09-08 8:19 UTC (permalink / raw)
To: stable; +Cc: Eric Dumazet, Kuniyuki Iwashima, Jakub Kicinski, Sasha Levin,
netdev
[ Upstream commit 858d2a4f67ff69e645a43487ef7ea7f28f06deae ]
Code in tcp_v6_syn_recv_sock() after the call to tcp_v4_syn_recv_sock()
is done too late.
After tcp_v4_syn_recv_sock(), the child socket is already visible
from TCP ehash table and other cpus might use it.
Since newinet->pinet6 is still pointing to the listener ipv6_pinfo
bad things can happen as syzbot found.
Move the problematic code in tcp_v6_mapped_child_init()
and call this new helper from tcp_v4_syn_recv_sock() before
the ehash insertion.
This allows the removal of one tcp_sync_mss(), since
tcp_v4_syn_recv_sock() will call it with the correct
context.
Backport notes (6.12.y):
The mainline commit does not apply cleanly to 6.12 because
ipv6_fl_list was later moved from struct ipv6_pinfo into
struct inet_sock. On 6.12 ipv6_fl_list still lives inside
ipv6_pinfo, so the memcpy of the parent ipv6_pinfo into the
child covers it, and the new helper must therefore keep the
ipv6_fl_list initialization in the post-memcpy block (as done
here). No other logic changes.
CVE-2026-43198
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+937b5bbb6a815b3e5d0b@syzkaller.appspotmail.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[mpf: backport to 6.12.y; keep ipv6_fl_list initialization in the
post-memcpy block since ipv6_fl_list still lives in struct
ipv6_pinfo on 6.12 (mainline moved it into struct inet_sock
after 6.12)]
Signed-off-by: Michael Pfeifroth <michael.pfeifroth@westermo.com>
---
Index: b/include/net/inet_connection_sock.h
===================================================================
--- a/include/net/inet_connection_sock.h 2026-07-04 13:42:28.000000000 +0200
+++ b/include/net/inet_connection_sock.h 2026-08-03 11:15:50.785059353 +0200
@@ -42,7 +42,9 @@ struct inet_connection_sock_af_ops {
struct request_sock *req,
struct dst_entry *dst,
struct request_sock *req_unhash,
- bool *own_req);
+ bool *own_req,
+ void (*opt_child_init)(struct sock *newsk,
+ const struct sock *sk));
u16 net_header_len;
u16 net_frag_header_len;
u16 sockaddr_len;
Index: b/include/net/tcp.h
===================================================================
--- a/include/net/tcp.h 2026-08-03 11:15:41.286991513 +0200
+++ b/include/net/tcp.h 2026-08-03 11:15:50.789059382 +0200
@@ -460,7 +460,9 @@ struct sock *tcp_v4_syn_recv_sock(const
struct request_sock *req,
struct dst_entry *dst,
struct request_sock *req_unhash,
- bool *own_req);
+ bool *own_req,
+ void (*opt_child_init)(struct sock *newsk,
+ const struct sock *sk));
int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
int tcp_connect(struct sock *sk);
Index: b/net/ipv4/syncookies.c
===================================================================
--- a/net/ipv4/syncookies.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/ipv4/syncookies.c 2026-08-03 11:15:50.792059404 +0200
@@ -199,7 +199,7 @@ struct sock *tcp_get_cookie_sock(struct
bool own_req;
child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
- NULL, &own_req);
+ NULL, &own_req, NULL);
if (child) {
refcount_set(&req->rsk_refcnt, 1);
tcp_sk(child)->tsoffset = tsoff;
Index: b/net/ipv4/tcp_fastopen.c
===================================================================
--- a/net/ipv4/tcp_fastopen.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/ipv4/tcp_fastopen.c 2026-08-03 11:15:50.795059426 +0200
@@ -247,7 +247,7 @@ static struct sock *tcp_fastopen_create_
bool own_req;
child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
- NULL, &own_req);
+ NULL, &own_req, NULL);
if (!child)
return NULL;
Index: b/net/ipv4/tcp_ipv4.c
===================================================================
--- a/net/ipv4/tcp_ipv4.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/ipv4/tcp_ipv4.c 2026-08-03 11:15:50.799059455 +0200
@@ -1564,7 +1564,9 @@ struct sock *tcp_v4_syn_recv_sock(const
struct request_sock *req,
struct dst_entry *dst,
struct request_sock *req_unhash,
- bool *own_req)
+ bool *own_req,
+ void (*opt_child_init)(struct sock *newsk,
+ const struct sock *sk))
{
struct inet_request_sock *ireq;
bool found_dup_sk = false;
@@ -1620,6 +1622,10 @@ struct sock *tcp_v4_syn_recv_sock(const
}
sk_setup_caps(newsk, dst);
+#if IS_ENABLED(CONFIG_IPV6)
+ if (opt_child_init)
+ opt_child_init(newsk, sk);
+#endif
tcp_ca_openreq_child(newsk, dst);
tcp_sync_mss(newsk, dst_mtu(dst));
Index: b/net/ipv4/tcp_minisocks.c
===================================================================
--- a/net/ipv4/tcp_minisocks.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/ipv4/tcp_minisocks.c 2026-08-03 11:15:50.802059477 +0200
@@ -798,7 +798,7 @@ struct sock *tcp_check_req(struct sock *
* socket is created, wait for troubles.
*/
child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
- req, &own_req);
+ req, &own_req, NULL);
if (!child)
goto listen_overflow;
Index: b/net/ipv6/tcp_ipv6.c
===================================================================
--- a/net/ipv6/tcp_ipv6.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/ipv6/tcp_ipv6.c 2026-08-03 11:16:23.691310616 +0200
@@ -1186,11 +1186,48 @@ static void tcp_v6_restore_cb(struct sk_
sizeof(struct inet6_skb_parm));
}
+/* Called from tcp_v4_syn_recv_sock() for v6_mapped children. */
+static void tcp_v6_mapped_child_init(struct sock *newsk, const struct sock *sk)
+{
+ struct inet_sock *newinet = inet_sk(newsk);
+ struct ipv6_pinfo *newnp;
+
+ newinet->pinet6 = newnp = tcp_inet6_sk(newsk);
+
+ memcpy(newnp, tcp_inet6_sk(sk), sizeof(struct ipv6_pinfo));
+
+ newnp->saddr = newsk->sk_v6_rcv_saddr;
+
+ inet_csk(newsk)->icsk_af_ops = &ipv6_mapped;
+ if (sk_is_mptcp(newsk))
+ mptcpv6_handle_mapped(newsk, true);
+ newsk->sk_backlog_rcv = tcp_v4_do_rcv;
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
+ tcp_sk(newsk)->af_specific = &tcp_sock_ipv6_mapped_specific;
+#endif
+
+ newnp->ipv6_mc_list = NULL;
+ newnp->ipv6_ac_list = NULL;
+ newnp->ipv6_fl_list = NULL;
+ newnp->pktoptions = NULL;
+ newnp->opt = NULL;
+
+ /* tcp_v4_syn_recv_sock() has initialized newinet->mc_{index,ttl} */
+ newnp->mcast_oif = newinet->mc_index;
+ newnp->mcast_hops = newinet->mc_ttl;
+
+ newnp->rcv_flowinfo = 0;
+ if (inet6_test_bit(REPFLOW, sk))
+ newnp->flow_label = 0;
+}
+
static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
struct dst_entry *dst,
struct request_sock *req_unhash,
- bool *own_req)
+ bool *own_req,
+ void (*opt_child_init)(struct sock *newsk,
+ const struct sock *sk))
{
struct inet_request_sock *ireq;
struct ipv6_pinfo *newnp;
@@ -1206,59 +1243,10 @@ static struct sock *tcp_v6_syn_recv_sock
#endif
struct flowi6 fl6;
- if (skb->protocol == htons(ETH_P_IP)) {
- /*
- * v6 mapped
- */
-
- newsk = tcp_v4_syn_recv_sock(sk, skb, req, dst,
- req_unhash, own_req);
-
- if (!newsk)
- return NULL;
-
- inet_sk(newsk)->pinet6 = tcp_inet6_sk(newsk);
-
- newnp = tcp_inet6_sk(newsk);
- newtp = tcp_sk(newsk);
-
- memcpy(newnp, np, sizeof(struct ipv6_pinfo));
-
- newnp->saddr = newsk->sk_v6_rcv_saddr;
-
- inet_csk(newsk)->icsk_af_ops = &ipv6_mapped;
- if (sk_is_mptcp(newsk))
- mptcpv6_handle_mapped(newsk, true);
- newsk->sk_backlog_rcv = tcp_v4_do_rcv;
-#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
- newtp->af_specific = &tcp_sock_ipv6_mapped_specific;
-#endif
-
- newnp->ipv6_mc_list = NULL;
- newnp->ipv6_ac_list = NULL;
- newnp->ipv6_fl_list = NULL;
- newnp->pktoptions = NULL;
- newnp->opt = NULL;
- newnp->mcast_oif = inet_iif(skb);
- newnp->mcast_hops = ip_hdr(skb)->ttl;
- newnp->rcv_flowinfo = 0;
- if (inet6_test_bit(REPFLOW, sk))
- newnp->flow_label = 0;
-
- /*
- * No need to charge this sock to the relevant IPv6 refcnt debug socks count
- * here, tcp_create_openreq_child now does this for us, see the comment in
- * that function for the gory details. -acme
- */
-
- /* It is tricky place. Until this moment IPv4 tcp
- worked with IPv6 icsk.icsk_af_ops.
- Sync it now.
- */
- tcp_sync_mss(newsk, inet_csk(newsk)->icsk_pmtu_cookie);
-
- return newsk;
- }
+ if (skb->protocol == htons(ETH_P_IP))
+ return tcp_v4_syn_recv_sock(sk, skb, req, dst,
+ req_unhash, own_req,
+ tcp_v6_mapped_child_init);
ireq = inet_rsk(req);
Index: b/net/mptcp/subflow.c
===================================================================
--- a/net/mptcp/subflow.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/mptcp/subflow.c 2026-08-03 11:15:50.805059498 +0200
@@ -788,7 +788,9 @@ static struct sock *subflow_syn_recv_soc
struct request_sock *req,
struct dst_entry *dst,
struct request_sock *req_unhash,
- bool *own_req)
+ bool *own_req,
+ void (*opt_child_init)(struct sock *newsk,
+ const struct sock *sk))
{
struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk);
struct mptcp_subflow_request_sock *subflow_req;
@@ -834,7 +836,7 @@ static struct sock *subflow_syn_recv_soc
create_child:
child = listener->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
- req_unhash, own_req);
+ req_unhash, own_req, opt_child_init);
if (child && *own_req) {
struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child);
Index: b/net/smc/af_smc.c
===================================================================
--- a/net/smc/af_smc.c 2026-07-04 13:42:28.000000000 +0200
+++ b/net/smc/af_smc.c 2026-08-03 11:15:50.809059527 +0200
@@ -119,7 +119,9 @@ static struct sock *smc_tcp_syn_recv_soc
struct request_sock *req,
struct dst_entry *dst,
struct request_sock *req_unhash,
- bool *own_req)
+ bool *own_req,
+ void (*opt_child_init)(struct sock *newsk,
+ const struct sock *sk))
{
struct smc_sock *smc;
struct sock *child;
@@ -144,7 +146,7 @@ static struct sock *smc_tcp_syn_recv_soc
/* passthrough to original syn recv sock fct */
child = smc->ori_af_ops->syn_recv_sock(sk, skb, req, dst, req_unhash,
- own_req);
+ own_req, opt_child_init);
/* child must not inherit smc or its ops */
if (child) {
rcu_assign_sk_user_data(child, NULL);
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