netdev - Re: [PATCH net] tun: add mutex_unlock() call and napi.skb clearing in tun_get

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Message-Id: <20200123.114421.1414769180741959285.davem@davemloft.net>
Date:   Thu, 23 Jan 2020 11:44:21 +0100 (CET)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzkaller@...glegroups.com, ppenkov@...gle.com, willemb@...gle.com
Subject: Re: [PATCH net] tun: add mutex_unlock() call and napi.skb clearing
 in tun_get_user()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 22 Jan 2020 09:07:35 -0800

> If both IFF_NAPI_FRAGS mode and XDP are enabled, and the XDP program
> consumes the skb, we need to clear the napi.skb (or risk
> a use-after-free) and release the mutex (or risk a deadlock)
> 
> WARNING: lock held when returning to user space!
> 5.5.0-rc6-syzkaller #0 Not tainted
> ------------------------------------------------
> syz-executor.0/455 is leaving the kernel with locks still held!
> 1 lock held by syz-executor.0/455:
>  #0: ffff888098f6e748 (&tfile->napi_mutex){+.+.}, at: tun_get_user+0x1604/0x3fc0 drivers/net/tun.c:1835
> 
> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable, thanks Eric.