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Subject[PATCH 4.9 168/171] tcp/dccp: fix possible race __inet_lookup_established()
Date
From: Eric Dumazet <edumazet@google.com>

commit 8dbd76e79a16b45b2ccb01d2f2e08dbf64e71e40 upstream.

Michal Kubecek and Firo Yang did a very nice analysis of crashes
happening in __inet_lookup_established().

Since a TCP socket can go from TCP_ESTABLISH to TCP_LISTEN
(via a close()/socket()/listen() cycle) without a RCU grace period,
I should not have changed listeners linkage in their hash table.

They must use the nulls protocol (Documentation/RCU/rculist_nulls.txt),
so that a lookup can detect a socket in a hash list was moved in
another one.

Since we added code in commit d296ba60d8e2 ("soreuseport: Resolve
merge conflict for v4/v6 ordering fix"), we have to add
hlist_nulls_add_tail_rcu() helper.

Fixes: 3b24d854cb35 ("tcp/dccp: do not touch listener sk_refcnt under synflood")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Michal Kubecek <mkubecek@suse.cz>
Reported-by: Firo Yang <firo.yang@suse.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Link: https://lore.kernel.org/netdev/20191120083919.GH27852@unicorn.suse.cz/
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
[stable-4.9: we also need to update code in __inet_lookup_listener() and
inet6_lookup_listener() which has been removed in 5.0-rc1.]
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/rculist_nulls.h | 37 +++++++++++++++++++++++++++++++++++++
include/net/inet_hashtables.h | 12 +++++++++---
include/net/sock.h | 5 +++++
net/ipv4/inet_diag.c | 3 ++-
net/ipv4/inet_hashtables.c | 18 +++++++++---------
net/ipv4/tcp_ipv4.c | 7 ++++---
net/ipv6/inet6_hashtables.c | 3 ++-
7 files changed, 68 insertions(+), 17 deletions(-)

--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -100,6 +100,43 @@ static inline void hlist_nulls_add_head_
}

/**
+ * hlist_nulls_add_tail_rcu
+ * @n: the element to add to the hash list.
+ * @h: the list to add to.
+ *
+ * Description:
+ * Adds the specified element to the specified hlist_nulls,
+ * while permitting racing traversals.
+ *
+ * The caller must take whatever precautions are necessary
+ * (such as holding appropriate locks) to avoid racing
+ * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
+ * or hlist_nulls_del_rcu(), running on this same list.
+ * However, it is perfectly legal to run concurrently with
+ * the _rcu list-traversal primitives, such as
+ * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
+ * problems on Alpha CPUs. Regardless of the type of CPU, the
+ * list-traversal primitive must be guarded by rcu_read_lock().
+ */
+static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
+ struct hlist_nulls_head *h)
+{
+ struct hlist_nulls_node *i, *last = NULL;
+
+ /* Note: write side code, so rcu accessors are not needed. */
+ for (i = h->first; !is_a_nulls(i); i = i->next)
+ last = i;
+
+ if (last) {
+ n->next = last->next;
+ n->pprev = &last->next;
+ rcu_assign_pointer(hlist_next_rcu(last), n);
+ } else {
+ hlist_nulls_add_head_rcu(n, h);
+ }
+}
+
+/**
* hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
* @tpos: the type * to use as a loop cursor.
* @pos: the &struct hlist_nulls_node to use as a loop cursor.
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -98,12 +98,18 @@ struct inet_bind_hashbucket {
struct hlist_head chain;
};

-/*
- * Sockets can be hashed in established or listening table
+/* Sockets can be hashed in established or listening table.
+ * We must use different 'nulls' end-of-chain value for all hash buckets :
+ * A socket might transition from ESTABLISH to LISTEN state without
+ * RCU grace period. A lookup in ehash table needs to handle this case.
*/
+#define LISTENING_NULLS_BASE (1U << 29)
struct inet_listen_hashbucket {
spinlock_t lock;
- struct hlist_head head;
+ union {
+ struct hlist_head head;
+ struct hlist_nulls_head nulls_head;
+ };
};

/* This is for listening sockets, thus all sockets which possess wildcards. */
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -661,6 +661,11 @@ static inline void __sk_nulls_add_node_r
hlist_nulls_add_head_rcu(&sk->sk_nulls_node, list);
}

+static inline void __sk_nulls_add_node_tail_rcu(struct sock *sk, struct hlist_nulls_head *list)
+{
+ hlist_nulls_add_tail_rcu(&sk->sk_nulls_node, list);
+}
+
static inline void sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_head *list)
{
sock_hold(sk);
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -868,12 +868,13 @@ void inet_diag_dump_icsk(struct inet_has

for (i = s_i; i < INET_LHTABLE_SIZE; i++) {
struct inet_listen_hashbucket *ilb;
+ struct hlist_nulls_node *node;
struct sock *sk;

num = 0;
ilb = &hashinfo->listening_hash[i];
spin_lock_bh(&ilb->lock);
- sk_for_each(sk, &ilb->head) {
+ sk_nulls_for_each(sk, node, &ilb->nulls_head) {
struct inet_sock *inet = inet_sk(sk);

if (!net_eq(sock_net(sk), net))
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -218,9 +218,10 @@ struct sock *__inet_lookup_listener(stru
int score, hiscore = 0, matches = 0, reuseport = 0;
bool exact_dif = inet_exact_dif_match(net, skb);
struct sock *sk, *result = NULL;
+ struct hlist_nulls_node *node;
u32 phash = 0;

- sk_for_each_rcu(sk, &ilb->head) {
+ sk_nulls_for_each_rcu(sk, node, &ilb->nulls_head) {
score = compute_score(sk, net, hnum, daddr, dif, exact_dif);
if (score > hiscore) {
reuseport = sk->sk_reuseport;
@@ -441,10 +442,11 @@ static int inet_reuseport_add_sock(struc
bool match_wildcard))
{
struct inet_bind_bucket *tb = inet_csk(sk)->icsk_bind_hash;
+ const struct hlist_nulls_node *node;
struct sock *sk2;
kuid_t uid = sock_i_uid(sk);

- sk_for_each_rcu(sk2, &ilb->head) {
+ sk_nulls_for_each_rcu(sk2, node, &ilb->nulls_head) {
if (sk2 != sk &&
sk2->sk_family == sk->sk_family &&
ipv6_only_sock(sk2) == ipv6_only_sock(sk) &&
@@ -482,9 +484,9 @@ int __inet_hash(struct sock *sk, struct
}
if (IS_ENABLED(CONFIG_IPV6) && sk->sk_reuseport &&
sk->sk_family == AF_INET6)
- hlist_add_tail_rcu(&sk->sk_node, &ilb->head);
+ __sk_nulls_add_node_tail_rcu(sk, &ilb->nulls_head);
else
- hlist_add_head_rcu(&sk->sk_node, &ilb->head);
+ __sk_nulls_add_node_rcu(sk, &ilb->nulls_head);
sock_set_flag(sk, SOCK_RCU_FREE);
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
unlock:
@@ -527,10 +529,7 @@ void inet_unhash(struct sock *sk)
spin_lock_bh(lock);
if (rcu_access_pointer(sk->sk_reuseport_cb))
reuseport_detach_sock(sk);
- if (listener)
- done = __sk_del_node_init(sk);
- else
- done = __sk_nulls_del_node_init_rcu(sk);
+ done = __sk_nulls_del_node_init_rcu(sk);
if (done)
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
spin_unlock_bh(lock);
@@ -666,7 +665,8 @@ void inet_hashinfo_init(struct inet_hash

for (i = 0; i < INET_LHTABLE_SIZE; i++) {
spin_lock_init(&h->listening_hash[i].lock);
- INIT_HLIST_HEAD(&h->listening_hash[i].head);
+ INIT_HLIST_NULLS_HEAD(&h->listening_hash[i].nulls_head,
+ i + LISTENING_NULLS_BASE);
}
}
EXPORT_SYMBOL_GPL(inet_hashinfo_init);
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1917,13 +1917,14 @@ static void *listening_get_next(struct s
struct tcp_iter_state *st = seq->private;
struct net *net = seq_file_net(seq);
struct inet_listen_hashbucket *ilb;
+ struct hlist_nulls_node *node;
struct sock *sk = cur;

if (!sk) {
get_head:
ilb = &tcp_hashinfo.listening_hash[st->bucket];
spin_lock_bh(&ilb->lock);
- sk = sk_head(&ilb->head);
+ sk = sk_nulls_head(&ilb->nulls_head);
st->offset = 0;
goto get_sk;
}
@@ -1931,9 +1932,9 @@ get_head:
++st->num;
++st->offset;

- sk = sk_next(sk);
+ sk = sk_nulls_next(sk);
get_sk:
- sk_for_each_from(sk) {
+ sk_nulls_for_each_from(sk, node) {
if (!net_eq(sock_net(sk), net))
continue;
if (sk->sk_family == st->family)
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -133,9 +133,10 @@ struct sock *inet6_lookup_listener(struc
int score, hiscore = 0, matches = 0, reuseport = 0;
bool exact_dif = inet6_exact_dif_match(net, skb);
struct sock *sk, *result = NULL;
+ struct hlist_nulls_node *node;
u32 phash = 0;

- sk_for_each(sk, &ilb->head) {
+ sk_nulls_for_each(sk, node, &ilb->nulls_head) {
score = compute_score(sk, net, hnum, daddr, dif, exact_dif);
if (score > hiscore) {
reuseport = sk->sk_reuseport;

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