netdev - Re: [PATCH net v2 1/2] tun: publish tfile after it's fully initialized

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Message-Id: <20190110.062624.2083409199405985770.davem@davemloft.net>
Date:   Thu, 10 Jan 2019 06:26:24 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     sdf@...gle.com
Cc:     netdev@...r.kernel.org, jasowang@...hat.com, brouer@...hat.com,
        mst@...hat.com, edumazet@...gle.com, syzkaller@...glegroups.com
Subject: Re: [PATCH net v2 1/2] tun: publish tfile after it's fully
 initialized

From: Stanislav Fomichev <sdf@...gle.com>
Date: Mon,  7 Jan 2019 13:38:38 -0800

> BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1
> Call Trace:
 ...
> 
> I think there is a subtle race between sending a packet via tap and
> attaching it:
> 
> CPU0:                    CPU1:
> tun_chr_ioctl(TUNSETIFF)
 ...
> Move rcu_assign_pointer(tfile->tun) and rcu_assign_pointer(tun->tfiles) to
> be the last thing we do in tun_attach(); this should guarantee that when we
> call tun_get() we always get an initialized object.
> 
> v2 changes:
> * remove extra napi_mutex locks/unlocks for napi operations
> 
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>

Applied and queued up for -stable.

Please, the next time you submit a patch series, provide a proper header
posting.

Thank you.