netdev - Re: [PATCH net] net/packet: fix race in tpacket

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Message-Id: <20190815.140035.145028724115387751.davem@davemloft.net>
Date:   Thu, 15 Aug 2019 14:00:35 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] net/packet: fix race in tpacket_snd()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 14 Aug 2019 02:11:57 -0700

> packet_sendmsg() checks tx_ring.pg_vec to decide
> if it must call tpacket_snd().
> 
> Problem is that the check is lockless, meaning another thread
> can issue a concurrent setsockopt(PACKET_TX_RING ) to flip
> tx_ring.pg_vec back to NULL.
> 
> Given that tpacket_snd() grabs pg_vec_lock mutex, we can
> perform the check again to solve the race.
> 
> syzbot reported :
 ...
> Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable.