netdev - Re: [PATCH net] net/smc: Transitional solution for clcsock race issue

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Message-ID: <ad5c1c9b-5d9e-cd0f-88c7-4420bc9ed0e5@linux.alibaba.com>
Date:   Fri, 21 Jan 2022 15:05:02 +0800
From:   Wen Gu <guwen@...ux.alibaba.com>
To:     kgraul@...ux.ibm.com, davem@...emloft.net, kuba@...nel.org
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/smc: Transitional solution for clcsock race issue


On 2022/1/13 11:02 pm, Wen Gu wrote:
> We encountered a crash in smc_setsockopt() and it is caused by
> accessing smc->clcsock after clcsock was released.
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000020
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
>   PGD 0 P4D 0
>   Oops: 0000 [#1] PREEMPT SMP PTI
>   CPU: 1 PID: 50309 Comm: nginx Kdump: loaded Tainted: G E     5.16.0-rc4+ #53
>   RIP: 0010:smc_setsockopt+0x59/0x280 [smc]
>   Call Trace:
>    <TASK>
>    __sys_setsockopt+0xfc/0x190
>    __x64_sys_setsockopt+0x20/0x30
>    do_syscall_64+0x34/0x90
>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>   RIP: 0033:0x7f16ba83918e
>    </TASK>
> 
> This patch tries to fix it by holding clcsock_release_lock and
> checking whether clcsock has already been released before access.
> 
> In case that a crash of the same reason happens in smc_getsockopt()
> or smc_switch_to_fallback(), this patch also checkes smc->clcsock
> in them too. And the caller of smc_switch_to_fallback() will identify
> whether fallback succeeds according to the return value.
> 
> Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
> ---
>   net/smc/af_smc.c | 63 +++++++++++++++++++++++++++++++++++++++++++++-----------
>   1 file changed, 51 insertions(+), 12 deletions(-)
> 

Sorry for bothering, just wonder if this patch needs further improvements?

The previous discussion can be found in:
https://lore.kernel.org/lkml/5dd7ffd1-28e2-24cc-9442-1defec27375e@linux.ibm.com/T/

I sent this patch with a new subject instead of sending a v2 of the previously
discussed patch because I think the original subject seems not appropriate anymore
after introducing check of clcsock in smc_switch_to_fallback().

Thanks,
Wen Gu