From: Jakub Kicinski <kuba@kernel.org>
To: Eric Dumazet <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
Neal Cardwell <ncardwell@google.com>,
Kuniyuki Iwashima <kuniyu@google.com>,
netdev@vger.kernel.org, eric.dumazet@gmail.com
Subject: Re: [PATCH net] tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction
Date: Mon, 11 May 2026 13:23:25 -0700 [thread overview]
Message-ID: <20260511132325.54be1fe7@kernel.org> (raw)
In-Reply-To: <20260511151559.1916614-1-edumazet@google.com>
On Mon, 11 May 2026 15:15:59 +0000 Eric Dumazet wrote:
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index d13d49bfef19457cc5902cb556605a80f4c0ab2c..079f2324a3a777cfe30dd59777c9d3d6d9a6bae0 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1641,6 +1641,7 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
> reset:
> tcp_v6_send_reset(sk, skb, sk_rst_convert_drop_reason(reason));
> discard:
> + __this_cpu_write(tcp_tw_isn, 0);
> if (opt_skb)
> __kfree_skb(opt_skb);
> sk_skb_reason_drop(sk, skb, reason);
> @@ -1839,6 +1840,7 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
> }
> }
>
> + DEBUG_NET_WARN_ON_ONCE(__this_cpu_read(tcp_tw_isn));
> process:
> if (static_branch_unlikely(&ip6_min_hopcount)) {
> /* min_hopcount can be changed concurrently from do_ipv6_setsockopt() */
> @@ -1913,6 +1915,7 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
> }
>
> discard_it:
> + __this_cpu_write(tcp_tw_isn, 0);
> SKB_DR_OR(drop_reason, NOT_SPECIFIED);
> sk_skb_reason_drop(sk, skb, drop_reason);
> return 0;
CI says:
[ 288.637769][ T3492] BUG: using __this_cpu_write() in preemptible [00000000] code: python3/3492
[ 288.638116][ T3492] caller is tcp_v6_do_rcv+0x204/0x1cb0
[ 288.638240][ T3492] CPU: 1 UID: 0 PID: 3492 Comm: python3 Not tainted 7.1.0-rc2-virtme #1 PREEMPT(full)
[ 288.638245][ T3492] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 288.638247][ T3492] Call Trace:
[ 288.638248][ T3492] <TASK>
[ 288.638250][ T3492] dump_stack_lvl+0x6f/0xa0
[ 288.638257][ T3492] check_preemption_disabled+0xdb/0xf0
[ 288.638261][ T3492] tcp_v6_do_rcv+0x204/0x1cb0
[ 288.638265][ T3492] __release_sock+0x135/0x3a0
[ 288.638272][ T3492] release_sock+0x19c/0x240
[ 288.638275][ T3492] tcp_sendmsg+0x39/0x50
[ 288.638279][ T3492] __sys_sendto+0x2c9/0x400
[ 288.638282][ T3492] ? __ia32_sys_getpeername+0xd0/0xd0
[ 288.638288][ T3492] ? sock_ioctl+0x3cb/0x5f0
[ 288.638294][ T3492] ? find_held_lock+0x2b/0x80
[ 288.638299][ T3492] ? __lock_release.isra.0+0x6b/0x1a0
[ 288.638302][ T3492] __x64_sys_sendto+0xe4/0x1f0
[ 288.638304][ T3492] ? trace_irq_enable.constprop.0+0x9b/0x180
[ 288.638308][ T3492] ? lockdep_hardirqs_on+0x8c/0x130
[ 288.638310][ T3492] ? do_syscall_64+0x82/0xfc0
[ 288.638312][ T3492] do_syscall_64+0x117/0xfc0
[ 288.638314][ T3492] ? irq_exit_rcu+0x1a/0x30
[ 288.638318][ T3492] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 288.638321][ T3492] RIP: 0033:0x7f895f8fe08e
next prev parent reply other threads:[~2026-05-11 20:23 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-11 15:15 [PATCH net] tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction Eric Dumazet
2026-05-11 20:23 ` Jakub Kicinski [this message]
2026-05-12 6:18 ` [syzbot ci] " syzbot ci
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