netdev - Re: [RFC PATCH v1] tun: Cleanup error handling in tun_set

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Date:	Thu, 06 Aug 2009 20:40:32 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	ebiederm@...ssion.com, paul.moore@...com, netdev@...r.kernel.org
Subject: Re: [RFC PATCH v1] tun: Cleanup error handling in tun_set_iff()

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Fri, 7 Aug 2009 10:22:44 +1000

> tun: Extend RTNL lock coverage over whole ioctl
> 
> As it is, parts of the ioctl runs under the RTNL and parts of
> it do not.  The unlocked section is still protected by the BKL,
> but there can be subtle races.  For example, Eric Biederman and
> Paul Moore observed that if two threads tried to create two tun
> devices on the same file descriptor, then unexpected results
> may occur.
> 
> As there isn't anything in the ioctl that is expected to sleep
> indefinitely, we can prevent this from occurring by extending
> the RTNL lock coverage.
> 
> This also allows to get rid of the BKL.
> 
> Finally, I changed tun_get_iff to take a tun device in order to
> avoid calling tun_put which would dead-lockt as it also tries to
> take the RTNL lock.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

This looks good after a quick audit, Eric what say you?
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