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Date: Mon, 14 Dec 2009 21:11:57 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Neil Horman <nhorman@...driver.com>,
Netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: packet_sendmsg_spkt sleeping from invalid context
On Mon, Dec 14, 2009 at 08:24:23PM +0100, Eric Dumazet wrote:
> Thanks for the report Frederic.
>
> We could partly revert the original commit, but as we wanted to avoid touching
> device refcount, and af_packet might be the only real abuser, we could
> try following patch instead.
>
> Thanks
>
> [PATCH] packet: dont call sleeping function while holding rcu_read_lock()
>
> commit 654d1f8a019dfa06d (packet: less dev_put() calls)
> introduced a problem, calling a potentially sleeping function from a
> rcu_read_lock() protected section.
>
> Fix this by releasing lock before the sock_wmalloc() call.
> After skb allocation, we redo device lookup and appropriate tests.
>
> Reported-by: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---
> net/packet/af_packet.c | 36 +++++++++++++-----------------------
> 1 file changed, 13 insertions(+), 23 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 0205621..19ceadc 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -415,7 +415,7 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
> {
> struct sock *sk = sock->sk;
> struct sockaddr_pkt *saddr = (struct sockaddr_pkt *)msg->msg_name;
> - struct sk_buff *skb;
> + struct sk_buff *skb = NULL;
> struct net_device *dev;
> __be16 proto = 0;
> int err;
> @@ -437,6 +437,7 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
> */
>
> saddr->spkt_device[13] = 0;
> +retry:
> rcu_read_lock();
> dev = dev_get_by_name_rcu(sock_net(sk), saddr->spkt_device);
> err = -ENODEV;
> @@ -456,27 +457,21 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
> if (len > dev->mtu + dev->hard_header_len)
> goto out_unlock;
>
> - err = -ENOBUFS;
> - skb = sock_wmalloc(sk, len + LL_RESERVED_SPACE(dev), 0, GFP_KERNEL);
> -
> - /*
> - * If the write buffer is full, then tough. At this level the user
> - * gets to deal with the problem - do your own algorithmic backoffs.
> - * That's far more flexible.
> - */
> + if (!skb) {
> + size_t reserved = LL_RESERVED_SPACE(dev);
>
> - if (skb == NULL)
> - goto out_unlock;
> -
> - /*
> - * Fill it in
> - */
> + rcu_read_unlock();
> + skb = sock_wmalloc(sk, len + reserved, 0, GFP_KERNEL);
> + if (skb == NULL)
> + return -ENOBUFS;
> + skb_reserve(skb, reserved);
> + goto retry;
> + }
>
> /* FIXME: Save some space for broken drivers that write a
> * hard header at transmission time by themselves. PPP is the
> * notable one here. This should really be fixed at the driver level.
> */
> - skb_reserve(skb, LL_RESERVED_SPACE(dev));
> skb_reset_network_header(skb);
>
> /* Try to align data part correctly */
> @@ -494,20 +489,15 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
> skb->priority = sk->sk_priority;
> skb->mark = sk->sk_mark;
> if (err)
> - goto out_free;
> -
> - /*
> - * Now send it
> - */
> + goto out_unlock;
>
> dev_queue_xmit(skb);
> rcu_read_unlock();
> return len;
>
> -out_free:
> - kfree_skb(skb);
> out_unlock:
> rcu_read_unlock();
> + kfree_skb(skb);
> return err;
> }
>
Thanks, yeah it fixes the problem but unearthes a new one:
[ 32.428785] sched: BUG: sleeping function called from invalid context at mm/memory.c:3369
[ 32.454154] sched: in_atomic(): 1, irqs_disabled(): 0, pid: 3531, name: dhclient3
[ 32.472866] 1 lock held by dhclient3/3531:
[ 32.472872] #0: (rcu_read_lock){.+.+..}, at: [<ffffffff815d1a5e>] packet_sendmsg_spkt+0xce/0x340
[ 32.472900] Pid: 3531, comm: dhclient3 Tainted: G W 2.6.32-tip+ #135
[ 32.472906] Call Trace:
[ 32.472920] [<ffffffff81081403>] ? __debug_show_held_locks+0x13/0x30
[ 32.472933] [<ffffffff8103d6b8>] __might_sleep+0x118/0x140
[ 32.472944] [<ffffffff810f48cb>] might_fault+0x3b/0xd0
[ 32.472955] [<ffffffff81549c1e>] memcpy_fromiovec+0x6e/0xa0
[ 32.472965] [<ffffffff815d1c44>] packet_sendmsg_spkt+0x2b4/0x340
[ 32.472975] [<ffffffff815d1a5e>] ? packet_sendmsg_spkt+0xce/0x340
[ 32.472986] [<ffffffff8153e167>] sock_sendmsg+0x127/0x140
[ 32.472999] [<ffffffff8106f6e0>] ? autoremove_wake_function+0x0/0x40
[ 32.473009] [<ffffffff810f490b>] ? might_fault+0x7b/0xd0
[ 32.473019] [<ffffffff810f490b>] ? might_fault+0x7b/0xd0
[ 32.473030] [<ffffffff8154043a>] ? move_addr_to_kernel+0x6a/0x70
[ 32.473040] [<ffffffff8154052f>] sys_sendto+0xef/0x120
[ 32.473053] [<ffffffff81131709>] ? mntput_no_expire+0x29/0x110
[ 32.473067] [<ffffffff810027db>] system_call_fastpath+0x16/0x1b
And I guess you need to protect dev until the packet is submitted.
Looks tricky...
I've searched a kind of get_net_dev() but did not find any :)
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