netdev - Re: [RFC PATCH] tun: don't zeroize sock->file on detach

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Message-ID: <CAK6E8=cpODYa1xURk7BZBnWwx5q3OD8-xkCau7GNPn+1BS0oQQ@mail.gmail.com>
Date:	Wed, 8 Aug 2012 10:48:32 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"ruanzhijie@...mail.com" <ruanzhijie@...mail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: [RFC PATCH] tun: don't zeroize sock->file on detach

On Wed, Aug 8, 2012 at 5:53 AM, Stanislav Kinsbursky
<skinsbursky@...allels.com> wrote:
> Hi, Dave.
> What about this patch?
>
>
> On Wed, Jul 11, 2012 at 03:48:20PM +0400, Stanislav Kinsbursky wrote:
>>
>> This is a fix for bug, introduced in 3.4 kernel by commit
>> 1ab5ecb90cb6a3df1476e052f76a6e8f6511cb3d, which, among other things,
>> replaced
>> simple sock_put() by sk_release_kernel(). Below is sequence, which leads
>> to
>> oops for non-persistent devices:
>>
>> tun_chr_close()
>> tun_detach()                            <== tun->socket.file = NULL
>> tun_free_netdev()
>> sk_release_sock()
>> sock_release(sock->file == NULL)
>> iput(SOCK_INODE(sock))                  <== dereference on NULL pointer
>>
>> This patch just removes zeroing of socket's file from __tun_detach().
>> sock_release() will do this.
>>
>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>

I has tested this patch and it works (so my kernel stops crashing
using tun devices).

>> ---
>>  drivers/net/tun.c |    1 -
>>  1 files changed, 0 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index 987aeef..c1639f3 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -185,7 +185,6 @@ static void __tun_detach(struct tun_struct *tun)
>>         netif_tx_lock_bh(tun->dev);
>>         netif_carrier_off(tun->dev);
>>         tun->tfile = NULL;
>> -       tun->socket.file = NULL;
>>         netif_tx_unlock_bh(tun->dev);
>
> --
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