Re: [PATCH v3.10-rc7] net: fix kernel deadlock with interfacerename and netdev name retrieval.

[David Miller]

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Wed, 26 Jun 2013 09:33:34 -0700

> On Wed, 2013-06-26 at 17:23 +0200, Nicolas Schichan wrote:
>> When the kernel (compiled with CONFIG_PREEMPT=n) is performing the
>> rename of a network interface, it can end up waiting for a workqueue
>> to complete. If userland is able to invoke a SIOCGIFNAME ioctl or a
>> SO_BINDTODEVICE getsockopt in between, the kernel will deadlock due to
>> the fact that read_secklock_begin() will spin forever waiting for the
>> writer process (the one doing the interface rename) to update the
>> devnet_rename_seq sequence.
>> 
>> This patch fixes the problem by adding a helper (netdev_get_name())
>> and using it in the code handling the SIOCGIFNAME ioctl and
>> SO_BINDTODEVICE setsockopt.
>> 
>> The netdev_get_name() helper uses raw_seqcount_begin() to avoid
>> spinning forever, waiting for devnet_rename_seq->sequence to become
>> even. cond_resched() is used in the contended case, before retrying
>> the access to give the writer process a chance to finish.
>> 
>> The use of raw_seqcount_begin() will incur some unneeded work in the
>> reader process in the contended case, but this is better than
>> deadlocking the system.
>> 
>> Signed-off-by: Nicolas Schichan <nschichan@xxxxxxxxxx>
>> ---
> 
> This goes back to commit c91f6df2db49
> ("sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface
> name") in linux-3.8
> 
> Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>

Applied and queued up for -stable, thanks everyone.
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