[PATCH] net: inet: prevent lhash2 lookups from escaping into ehash
From: David Lee <hidden>
Date: 2026-07-31 14:05:15
Also in:
lkml
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
The lhash2 and ehash tables share sk_nulls_node. When a listening
socket is unhashed and rehashed as a connected socket while an RCU
listener lookup is walking it, the reader can follow the node's new
next pointer into ehash. inet_lhash2_lookup() and
inet6_lhash2_lookup() do not validate the terminal nulls marker, so
they can return an ehash entry under the listener lookup's
unreferenced ownership contract.
In particular, returning a TIME_WAIT socket makes the TCP receive
path consume a reference that the lookup never acquired. Repeated
races can free the object while it remains linked in the hash tables.
Skip non-listening sockets before scoring them. Also restart the walk
when its terminal nulls marker does not match the expected lhash2 slot,
as the established lookup already does.
Fixes: cae3873c5b3a ("net: inet: Retire port only listening_hash")
Bug found and triaged by OpenAI Security Research and
validated by Trail of Bits.
Assisted-by: Codex:gpt-5.6-sol gpt-5.5-cyber
Signed-off-by: Kyle Zeng <redacted>
---
Trail of Bits has a reproducer for this bug that triggers a
KASAN use-after-free and can share if needed.
net/ipv4/inet_hashtables.c | 20 ++++++++++++++++----
net/ipv6/inet6_hashtables.c | 20 ++++++++++++++++----
2 files changed, 32 insertions(+), 8 deletions(-)
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index ba0faa9ae..563c8af44 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c@@ -415,16 +415,23 @@ EXPORT_SYMBOL_GPL(inet_lookup_reuseport); /* called with rcu_read_lock() : No refcount taken on the socket */ static struct sock *inet_lhash2_lookup(const struct net *net, struct inet_listen_hashbucket *ilb2, + unsigned int slot, struct sk_buff *skb, int doff, const __be32 saddr, __be16 sport, const __be32 daddr, const unsigned short hnum, const int dif, const int sdif) { - struct sock *sk, *result = NULL; + struct sock *sk, *result; struct hlist_nulls_node *node; - int score, hiscore = 0; + int score, hiscore; +begin: + result = NULL; + hiscore = 0; sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) { + if (READ_ONCE(sk->sk_state) != TCP_LISTEN) + continue; + score = compute_score(sk, net, hnum, daddr, dif, sdif); if (score > hiscore) { result = inet_lookup_reuseport(net, sk, skb, doff,
@@ -437,6 +444,9 @@ static struct sock *inet_lhash2_lookup(const struct net *net, } } + if (get_nulls_value(node) != slot + LISTENING_NULLS_BASE) + goto begin; + return result; }
@@ -486,7 +496,8 @@ struct sock *__inet_lookup_listener(const struct net *net, hash2 = ipv4_portaddr_hash(net, daddr, hnum); ilb2 = inet_lhash2_bucket(hashinfo, hash2); - result = inet_lhash2_lookup(net, ilb2, skb, doff, + result = inet_lhash2_lookup(net, ilb2, + hash2 & hashinfo->lhash2_mask, skb, doff, saddr, sport, daddr, hnum, dif, sdif); if (result)
@@ -496,7 +507,8 @@ struct sock *__inet_lookup_listener(const struct net *net, hash2 = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum); ilb2 = inet_lhash2_bucket(hashinfo, hash2); - result = inet_lhash2_lookup(net, ilb2, skb, doff, + result = inet_lhash2_lookup(net, ilb2, + hash2 & hashinfo->lhash2_mask, skb, doff, saddr, sport, htonl(INADDR_ANY), hnum, dif, sdif); done:
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index b111b51d6..a9dfd47dd 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c@@ -184,16 +184,23 @@ EXPORT_SYMBOL_GPL(inet6_lookup_reuseport); /* called with rcu_read_lock() */ static struct sock *inet6_lhash2_lookup(const struct net *net, struct inet_listen_hashbucket *ilb2, + unsigned int slot, struct sk_buff *skb, int doff, const struct in6_addr *saddr, const __be16 sport, const struct in6_addr *daddr, const unsigned short hnum, const int dif, const int sdif) { - struct sock *sk, *result = NULL; + struct sock *sk, *result; struct hlist_nulls_node *node; - int score, hiscore = 0; + int score, hiscore; +begin: + result = NULL; + hiscore = 0; sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) { + if (READ_ONCE(sk->sk_state) != TCP_LISTEN) + continue; + score = compute_score(sk, net, hnum, daddr, dif, sdif); if (score > hiscore) { result = inet6_lookup_reuseport(net, sk, skb, doff,
@@ -206,6 +213,9 @@ static struct sock *inet6_lhash2_lookup(const struct net *net, } } + if (get_nulls_value(node) != slot + LISTENING_NULLS_BASE) + goto begin; + return result; }
@@ -260,7 +270,8 @@ struct sock *inet6_lookup_listener(const struct net *net, hash2 = ipv6_portaddr_hash(net, daddr, hnum); ilb2 = inet_lhash2_bucket(hashinfo, hash2); - result = inet6_lhash2_lookup(net, ilb2, skb, doff, + result = inet6_lhash2_lookup(net, ilb2, + hash2 & hashinfo->lhash2_mask, skb, doff, saddr, sport, daddr, hnum, dif, sdif); if (result)
@@ -270,7 +281,8 @@ struct sock *inet6_lookup_listener(const struct net *net, hash2 = ipv6_portaddr_hash(net, &in6addr_any, hnum); ilb2 = inet_lhash2_bucket(hashinfo, hash2); - result = inet6_lhash2_lookup(net, ilb2, skb, doff, + result = inet6_lhash2_lookup(net, ilb2, + hash2 & hashinfo->lhash2_mask, skb, doff, saddr, sport, &in6addr_any, hnum, dif, sdif); done: