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Date: Thu, 27 Feb 2020 16:33:51 +0900
From: Taehee Yoo <ap420073@...il.com>
To: subashab@...eaurora.org
Cc: David Miller <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, stranche@...eaurora.org,
Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 04/10] net: rmnet: fix suspicious RCU usage
On Thu, 27 Feb 2020 at 05:33, <subashab@...eaurora.org> wrote:
>
Hi,
Thank you for the review!
> On 2020-02-26 10:47, Taehee Yoo wrote:
> > rmnet_get_port() internally calls rcu_dereference_rtnl(),
> > which checks RTNL.
> > But rmnet_get_port() could be called by packet path.
> > The packet path is not protected by RTNL.
> > So, the suspicious RCU usage problem occurs.
> >
> > Test commands:
> > ip netns add nst
> > ip link add veth0 type veth peer name veth1
> > ip link set veth1 netns nst
> > ip link add rmnet0 link veth0 type rmnet mux_id 1
> > ip netns exec nst ip link add rmnet1 link veth1 type rmnet mux_id 1
> > ip netns exec nst ip link set veth1 up
> > ip netns exec nst ip link set rmnet1 up
> > ip netns exec nst ip a a 192.168.100.2/24 dev rmnet1
> > ip link set veth0 up
> > ip link set rmnet0 up
> > ip a a 192.168.100.1/24 dev rmnet0
> > ping 192.168.100.2
> >
> > Splat looks like:
> > [ 339.775811][ T969] =============================
> > [ 339.777204][ T969] WARNING: suspicious RCU usage
> > [ 339.778188][ T969] 5.5.0+ #407 Not tainted
> > [ 339.779123][ T969] -----------------------------
> > [ 339.780100][ T969]
> > drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c:389 suspicious
> > rcu_dereference_check() usage!
> > [ 339.781943][ T969]
> > [ 339.781943][ T969] other info that might help us debug this:
> > [ 339.781943][ T969]
> > [ 339.783475][ T969]
> > [ 339.783475][ T969] rcu_scheduler_active = 2, debug_locks = 1
> > [ 339.784656][ T969] 5 locks held by ping/969:
> > [ 339.785406][ T969] #0: ffff88804cb897f0 (sk_lock-AF_INET){+.+.},
> > at: raw_sendmsg+0xab8/0x2980
> > [ 339.786766][ T969] #1: ffffffff92925460 (rcu_read_lock_bh){....},
> > at: ip_finish_output2+0x243/0x2150
> > [ 339.788308][ T969] #2: ffffffff92925460 (rcu_read_lock_bh){....},
> > at: __dev_queue_xmit+0x213/0x2e10
> > [ 339.790662][ T969] #3: ffff88805a924158
> > (&dev->qdisc_running_key#3){+...}, at: ip_finish_output2+0x714/0x2150
> > [ 339.792072][ T969] #4: ffff88805b4fdc98
> > (&dev->qdisc_xmit_lock_key#3){+.-.}, at: sch_direct_xmit+0x1e2/0x1020
> > [ 339.793445][ T969]
> > [ 339.793445][ T969] stack backtrace:
> > [ 339.794691][ T969] CPU: 3 PID: 969 Comm: ping Not tainted 5.5.0+
> > #407
> > [ 339.795946][ T969] Hardware name: innotek GmbH
> > VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
> > [ 339.797621][ T969] Call Trace:
> > [ 339.798249][ T969] dump_stack+0x96/0xdb
> > [ 339.798847][ T969] rmnet_get_port.part.9+0x76/0x80 [rmnet]
> > [ 339.799583][ T969] rmnet_egress_handler+0x107/0x420 [rmnet]
> > [ 339.800350][ T969] ? sch_direct_xmit+0x1e2/0x1020
> > [ 339.801027][ T969] rmnet_vnd_start_xmit+0x3d/0xa0 [rmnet]
> > [ 339.801784][ T969] dev_hard_start_xmit+0x160/0x740
> > [ 339.802667][ T969] sch_direct_xmit+0x265/0x1020
> > [ ... ]
> >
> > Fixes: ceed73a2cf4a ("drivers: net: ethernet: qualcomm: rmnet: Initial
> > implementation")
> > Signed-off-by: Taehee Yoo <ap420073@...il.com>
> > ---
> > drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c | 13 ++++++-------
> > drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h | 2 +-
> > .../net/ethernet/qualcomm/rmnet/rmnet_handlers.c | 4 ++--
> > drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c | 2 ++
> > 4 files changed, 11 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> > b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> > index 7a7d0f521352..93642cdd3305 100644
> > --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> > +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c
> > @@ -382,11 +382,10 @@ struct rtnl_link_ops rmnet_link_ops __read_mostly
> > = {
> > .fill_info = rmnet_fill_info,
> > };
> >
> > -/* Needs either rcu_read_lock() or rtnl lock */
> > -struct rmnet_port *rmnet_get_port(struct net_device *real_dev)
> > +struct rmnet_port *rmnet_get_port_rcu(struct net_device *real_dev)
> > {
> > if (rmnet_is_real_dev_registered(real_dev))
> > - return rcu_dereference_rtnl(real_dev->rx_handler_data);
> > + return rcu_dereference(real_dev->rx_handler_data);
> > else
> > return NULL;
> > }
> > @@ -412,7 +411,7 @@ int rmnet_add_bridge(struct net_device *rmnet_dev,
> > struct rmnet_port *port, *slave_port;
> > int err;
> >
> > - port = rmnet_get_port(real_dev);
> > + port = rmnet_get_port_rtnl(real_dev);
> >
> > /* If there is more than one rmnet dev attached, its probably being
> > * used for muxing. Skip the briding in that case
> > @@ -427,7 +426,7 @@ int rmnet_add_bridge(struct net_device *rmnet_dev,
> > if (err)
> > return -EBUSY;
> >
> > - slave_port = rmnet_get_port(slave_dev);
> > + slave_port = rmnet_get_port_rtnl(slave_dev);
> > slave_port->rmnet_mode = RMNET_EPMODE_BRIDGE;
> > slave_port->bridge_ep = real_dev;
> >
> > @@ -445,11 +444,11 @@ int rmnet_del_bridge(struct net_device
> > *rmnet_dev,
> > struct net_device *real_dev = priv->real_dev;
> > struct rmnet_port *port, *slave_port;
> >
> > - port = rmnet_get_port(real_dev);
> > + port = rmnet_get_port_rtnl(real_dev);
> > port->rmnet_mode = RMNET_EPMODE_VND;
> > port->bridge_ep = NULL;
> >
> > - slave_port = rmnet_get_port(slave_dev);
> > + slave_port = rmnet_get_port_rtnl(slave_dev);
> > rmnet_unregister_real_device(slave_dev, slave_port);
> >
> > netdev_dbg(slave_dev, "removed from rmnet as slave\n");
> > diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h
> > b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h
> > index cd0a6bcbe74a..0d568dcfd65a 100644
> > --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h
> > +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h
> > @@ -65,7 +65,7 @@ struct rmnet_priv {
> > struct rmnet_priv_stats stats;
> > };
> >
> > -struct rmnet_port *rmnet_get_port(struct net_device *real_dev);
> > +struct rmnet_port *rmnet_get_port_rcu(struct net_device *real_dev);
> > struct rmnet_endpoint *rmnet_get_endpoint(struct rmnet_port *port, u8
> > mux_id);
> > int rmnet_add_bridge(struct net_device *rmnet_dev,
> > struct net_device *slave_dev,
> > diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> > b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> > index 1b74bc160402..074a8b326c30 100644
> > --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> > +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> > @@ -184,7 +184,7 @@ rx_handler_result_t rmnet_rx_handler(struct sk_buff
> > **pskb)
> > return RX_HANDLER_PASS;
> >
> > dev = skb->dev;
> > - port = rmnet_get_port(dev);
> > + port = rmnet_get_port_rcu(dev);
> >
> > switch (port->rmnet_mode) {
> > case RMNET_EPMODE_VND:
> > @@ -217,7 +217,7 @@ void rmnet_egress_handler(struct sk_buff *skb)
> > skb->dev = priv->real_dev;
> > mux_id = priv->mux_id;
> >
> > - port = rmnet_get_port(skb->dev);
> > + port = rmnet_get_port_rcu(skb->dev);
> > if (!port)
> > goto drop;
> >
> > diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c
> > b/drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c
> > index 509dfc895a33..a26e76e9d382 100644
> > --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c
> > +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c
> > @@ -50,7 +50,9 @@ static netdev_tx_t rmnet_vnd_start_xmit(struct
> > sk_buff *skb,
> >
> > priv = netdev_priv(dev);
> > if (priv->real_dev) {
>
> This rcu lock shouldn't be needed as it is acquired already in
> __dev_queue_xmit().
>
You're right, __dev_queue_xmit() already acquires rcu_read_lock_bh().
So, rcu_read_lock() is unnecessary in rmnet_vnd_start_xmit().
And I think rcu_dereference_bh() should be used instead of
rcu_dereference() in the rmnet_get_port_rcu().
I will send a v2 patch, which changes these two things.
Thank you!
Taehee Yoo
> > + rcu_read_lock();
> > rmnet_egress_handler(skb);
> > + rcu_read_unlock();
> > } else {
> > this_cpu_inc(priv->pcpu_stats->stats.tx_drops);
> > kfree_skb(skb);
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