netdev - Re: Race over table->data in proc_do_sync

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Date: Thu, 10 Aug 2023 09:20:28 +0300 (EEST)
From: Julian Anastasov <ja@....bg>
To: Sishuai Gong <sishuai.system@...il.com>
cc: horms@...ge.net.au,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        lvs-devel@...r.kernel.org
Subject: Re: Race over table->data in proc_do_sync_threshold()


	Hello,

On Wed, 9 Aug 2023, Sishuai Gong wrote:

> Hi,
> 
> We observed races over (struct ctl_table *) table->data when two threads
> are running proc_do_sync_threshold() in parallel, as shown below:
> 
> Thread-1			Thread-2
> memcpy(val, valp, sizeof(val)); memcpy(valp, val, sizeof(val));
> 
> This race probably would mess up table->data. Is it better to add a lock?

	We can put mutex_lock(&ipvs->sync_mutex) before the first
memcpy and to use two WRITE_ONCE instead of the second memcpy. But
this requires extra2 = ipvs in ip_vs_control_net_init_sysctl():

	tbl[idx].data = &ipvs->sysctl_sync_threshold;
+	tbl[idx].extra2 = ipvs;

	Will you provide patch?

Regards

--
Julian Anastasov <ja@....bg>