netdev - Re: [PATCH v3 net] tcp/dccp: Don't use timer_pending() in reqsk_queue

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Message-ID: <CANn89i+uoYGpV69RQPNb1gPpeDZf_qv1+M5KcThACQf4rrJfYg@mail.gmail.com>
Date: Tue, 15 Oct 2024 09:55:20 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v3 net] tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().

On Tue, Oct 15, 2024 at 12:33 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler().
>
>   """
>   We are seeing a use-after-free from a bpf prog attached to
>   trace_tcp_retransmit_synack. The program passes the req->sk to the
>   bpf_sk_storage_get_tracing kernel helper which does check for null
>   before using it.
>   """
>
> The commit 83fccfc3940c ("inet: fix potential deadlock in
> reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not
> to call del_timer_sync() from reqsk_timer_handler(), but it introduced a
> small race window.
>
> Before the timer is called, expire_timers() calls detach_timer(timer, true)
> to clear timer->entry.pprev and marks it as not pending.
>
> If reqsk_queue_unlink() checks timer_pending() just after expire_timers()
> calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will
> continue running and send multiple SYN+ACKs until it expires.
>
> The reported UAF could happen if req->sk is close()d earlier than the timer
> expiration, which is 63s by default.
>
>
> Fixes: 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()")
> Reported-by: Martin KaFai Lau <martin.lau@...nel.org>
> Closes: https://lore.kernel.org/netdev/eb6684d0-ffd9-4bdc-9196-33f690c25824@linux.dev/
> Link: https://lore.kernel.org/netdev/b55e2ca0-42f2-4b7c-b445-6ffd87ca74a0@linux.dev/ [1]
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>