netdev - Re: [PATCH net-next] net: ipv4: guard ip_mr

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Message-ID: <CADVnQynbzZJhfgAx_RK52PTcDG2A42JTFZQXGUKNctSq96sZxw@mail.gmail.com>
Date: Fri, 27 Jun 2025 08:35:40 -0400
From: Neal Cardwell <ncardwell@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, syzbot+f02fb9e43bd85c6c66ae@...kaller.appspotmail.com, 
	Petr Machata <petrm@...dia.com>, Roopa Prabhu <roopa@...dia.com>, 
	Nikolay Aleksandrov <razor@...ckwall.org>, Benjamin Poirier <bpoirier@...dia.com>, 
	Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next] net: ipv4: guard ip_mr_output() with rcu

On Fri, Jun 27, 2025 at 7:47 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> syzbot found at least one path leads to an ip_mr_output()
> without RCU being held.
>
> Add guard(rcu)() to fix this in a concise way.
>
> WARNING: CPU: 0 PID: 0 at net/ipv4/ipmr.c:2302 ip_mr_output+0xbb1/0xe70 net/ipv4/ipmr.c:2302
> Call Trace:
>  <IRQ>
>   igmp_send_report+0x89e/0xdb0 net/ipv4/igmp.c:799
>  igmp_timer_expire+0x204/0x510 net/ipv4/igmp.c:-1
>   call_timer_fn+0x17e/0x5f0 kernel/time/timer.c:1747
>   expire_timers kernel/time/timer.c:1798 [inline]
>   __run_timers kernel/time/timer.c:2372 [inline]
>   __run_timer_base+0x61a/0x860 kernel/time/timer.c:2384
>   run_timer_base kernel/time/timer.c:2393 [inline]
>   run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
>   handle_softirqs+0x286/0x870 kernel/softirq.c:579
>   __do_softirq kernel/softirq.c:613 [inline]
>   invoke_softirq kernel/softirq.c:453 [inline]
>   __irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
>   irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
>   instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
>   sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050
>
> Fixes: 35bec72a24ac ("net: ipv4: Add ip_mr_output()")
> Reported-by: syzbot+f02fb9e43bd85c6c66ae@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/685e841a.a00a0220.129264.0002.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Petr Machata <petrm@...dia.com>
> Cc: Roopa Prabhu <roopa@...dia.com>
> Cc: Nikolay Aleksandrov <razor@...ckwall.org>
> Cc: Benjamin Poirier <bpoirier@...dia.com>
> Cc: Ido Schimmel <idosch@...dia.com>
> ---

Reviewed-by: Neal Cardwell <ncardwell@...gle.com>

Thanks, Eric!

neal