This is a note to let you know that I've just added the patch titled
tcp: prevent concurrent execution of tcp_sk_exit_batch
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-prevent-concurrent-execution-of-tcp_sk_exit_batc.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 16672636b62931df1a8fe36b48d55b98b36d5b8b
Author: Florian Westphal <fw@xxxxxxxxx>
Date: Tue Aug 13 00:28:25 2024 +0200
tcp: prevent concurrent execution of tcp_sk_exit_batch
[ Upstream commit 565d121b69980637f040eb4d84289869cdaabedf ]
Its possible that two threads call tcp_sk_exit_batch() concurrently,
once from the cleanup_net workqueue, once from a task that failed to clone
a new netns. In the latter case, error unwinding calls the exit handlers
in reverse order for the 'failed' netns.
tcp_sk_exit_batch() calls tcp_twsk_purge().
Problem is that since commit b099ce2602d8 ("net: Batch inet_twsk_purge"),
this function picks up twsk in any dying netns, not just the one passed
in via exit_batch list.
This means that the error unwind of setup_net() can "steal" and destroy
timewait sockets belonging to the exiting netns.
This allows the netns exit worker to proceed to call
WARN_ON_ONCE(!refcount_dec_and_test(&net->ipv4.tcp_death_row.tw_refcount));
without the expected 1 -> 0 transition, which then splats.
At same time, error unwind path that is also running inet_twsk_purge()
will splat as well:
WARNING: .. at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210
...
refcount_dec include/linux/refcount.h:351 [inline]
inet_twsk_kill+0x758/0x9c0 net/ipv4/inet_timewait_sock.c:70
inet_twsk_deschedule_put net/ipv4/inet_timewait_sock.c:221
inet_twsk_purge+0x725/0x890 net/ipv4/inet_timewait_sock.c:304
tcp_sk_exit_batch+0x1c/0x170 net/ipv4/tcp_ipv4.c:3522
ops_exit_list+0x128/0x180 net/core/net_namespace.c:178
setup_net+0x714/0xb40 net/core/net_namespace.c:375
copy_net_ns+0x2f0/0x670 net/core/net_namespace.c:508
create_new_namespaces+0x3ea/0xb10 kernel/nsproxy.c:110
... because refcount_dec() of tw_refcount unexpectedly dropped to 0.
This doesn't seem like an actual bug (no tw sockets got lost and I don't
see a use-after-free) but as erroneous trigger of debug check.
Add a mutex to force strict ordering: the task that calls tcp_twsk_purge()
blocks other task from doing final _dec_and_test before mutex-owner has
removed all tw sockets of dying netns.
Fixes: e9bd0cca09d1 ("tcp: Don't allocate tcp_death_row outside of struct netns_ipv4.")
Reported-by: syzbot+8ea26396ff85d23a8929@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/netdev/0000000000003a5292061f5e4e19@xxxxxxxxxx/
Link: https://lore.kernel.org/netdev/20240812140104.GA21559@xxxxxxxxxxxxx/
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Reviewed-by: Jason Xing <kerneljasonxing@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://patch.msgid.link/20240812222857.29837-1-fw@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 6ef51d253abb7..96d235bcf5cb2 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -94,6 +94,8 @@ EXPORT_SYMBOL(tcp_hashinfo);
static DEFINE_PER_CPU(struct sock *, ipv4_tcp_sk);
+static DEFINE_MUTEX(tcp_exit_batch_mutex);
+
static u32 tcp_v4_init_seq(const struct sk_buff *skb)
{
return secure_tcp_seq(ip_hdr(skb)->daddr,
@@ -3304,6 +3306,16 @@ static void __net_exit tcp_sk_exit_batch(struct list_head *net_exit_list)
{
struct net *net;
+ /* make sure concurrent calls to tcp_sk_exit_batch from net_cleanup_work
+ * and failed setup_net error unwinding path are serialized.
+ *
+ * tcp_twsk_purge() handles twsk in any dead netns, not just those in
+ * net_exit_list, the thread that dismantles a particular twsk must
+ * do so without other thread progressing to refcount_dec_and_test() of
+ * tcp_death_row.tw_refcount.
+ */
+ mutex_lock(&tcp_exit_batch_mutex);
+
tcp_twsk_purge(net_exit_list);
list_for_each_entry(net, net_exit_list, exit_list) {
@@ -3311,6 +3323,8 @@ static void __net_exit tcp_sk_exit_batch(struct list_head *net_exit_list)
WARN_ON_ONCE(!refcount_dec_and_test(&net->ipv4.tcp_death_row.tw_refcount));
tcp_fastopen_ctx_destroy(net);
}
+
+ mutex_unlock(&tcp_exit_batch_mutex);
}
static struct pernet_operations __net_initdata tcp_sk_ops = {
