[PATCH v1 net-next 1/2] tcp: Do not allow buggy transitions between ehash and lhash2.
From: Kuniyuki Iwashima <kuniyu@google.com>
Date: 2026-09-04 03:36:07
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
The following state transitions have long been a playground for
syzbot, and recently AI joined in, reporting a lot more bugs.
* listen() + shutdown() + connect()
* connect() + connect(AF_UNSPEC) + listen()
All the fix attempts would add more code to the fast path, which
is not worth it.
Instead of playing whack-a-mole with these edge-case bugs,
let's disallow these transitions.
Note that unhashed_state is placed in the 4-byte hole after
icsk_pmtu_cookie.
$ pahole -C inet_connection_sock vmlinux
struct inet_connection_sock {
...
__u32 icsk_pmtu_cookie; /* 1208 4 */
unsigned char unhashed_state; /* 1212 1 */
/* XXX 3 bytes hole, try to pack */
Reported-by: Kyle Zeng <redacted>
Closes: https://lore.kernel.org/netdev/20260731140512.566464-1-david.lee@trailofbits.com/ (local)
Reported-by: Michal Luczaj <redacted>
Closes: https://lore.kernel.org/netdev/20260803-sockmap-lookup-tcp-leak-v2-0-306e025bfe66@rbox.co/ (local)
Reported-by: Hyunwoo Kim <redacted>
Closes: https://lore.kernel.org/netdev/20260824033331.1084971-1-imv4bel@gmail.com/ (local)
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
include/net/inet_connection_sock.h | 1 +
net/ipv4/inet_connection_sock.c | 1 +
net/ipv4/inet_hashtables.c | 11 +++++++++++
3 files changed, 13 insertions(+)
diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 433c2df23076..903499581db7 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h@@ -94,6 +94,7 @@ struct inet_connection_sock { u32 icsk_rto_max; __u32 icsk_delack_max; __u32 icsk_pmtu_cookie; + unsigned char unhashed_state; const struct tcp_congestion_ops *icsk_ca_ops; const struct inet_connection_sock_af_ops *icsk_af_ops; const struct tcp_ulp_ops *icsk_ulp_ops;
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 6257459bcee2..560ca861b6d0 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c@@ -1253,6 +1253,7 @@ struct sock *inet_csk_clone_lock(const struct sock *sk, memset(&newicsk->icsk_accept_queue, 0, sizeof(newicsk->icsk_accept_queue)); + newicsk->unhashed_state = 0; inet_sk_set_state(newsk, TCP_SYN_RECV); inet_clone_ulp(req, newsk, priority);
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index ba0faa9ae2bb..5abcb0debb27 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c@@ -803,6 +803,11 @@ int inet_hash(struct sock *sk) inet_init_ehash_secret(); WARN_ON(!sk_unhashed(sk)); + + if (unlikely(inet_csk(sk)->unhashed_state && + inet_csk(sk)->unhashed_state != TCP_LISTEN)) + return -EINVAL; + ilb2 = inet_lhash2_bucket_sk(hashinfo, sk); spin_lock(&ilb2->lock);
@@ -832,6 +837,9 @@ void inet_unhash(struct sock *sk) return; sock_rps_delete_flow(sk); + + inet_csk(sk)->unhashed_state = sk->sk_state; + if (sk->sk_state == TCP_LISTEN) { struct inet_listen_hashbucket *ilb2;
@@ -1058,6 +1066,9 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row, int ret, i, low, high; bool local_ports; + if (unlikely(inet_csk(sk)->unhashed_state == TCP_LISTEN)) + return -EINVAL; + if (port) { local_bh_disable(); ret = check_established(death_row, sk, port, NULL, false,
--
2.55.0.1003.g10538fe699-goog