This is a note to let you know that I've just added the patch titled
net: add a synchronize_net() in netdev_rx_handler_unregister()
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-add-a-synchronize_net-in-netdev_rx_handler_unregister.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f7417bbd93aa80dbd313f4ef0202572cb3fb48bc Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Fri, 29 Mar 2013 03:01:22 +0000
Subject: net: add a synchronize_net() in netdev_rx_handler_unregister()
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit 00cfec37484761a44a3b6f4675a54caa618210ae ]
commit 35d48903e97819 (bonding: fix rx_handler locking) added a race
in bonding driver, reported by Steven Rostedt who did a very good
diagnosis :
<quoting Steven>
I'm currently debugging a crash in an old 3.0-rt kernel that one of our
customers is seeing. The bug happens with a stress test that loads and
unloads the bonding module in a loop (I don't know all the details as
I'm not the one that is directly interacting with the customer). But the
bug looks to be something that may still be present and possibly present
in mainline too. It will just be much harder to trigger it in mainline.
In -rt, interrupts are threads, and can schedule in and out just like
any other thread. Note, mainline now supports interrupt threads so this
may be easily reproducible in mainline as well. I don't have the ability
to tell the customer to try mainline or other kernels, so my hands are
somewhat tied to what I can do.
But according to a core dump, I tracked down that the eth irq thread
crashed in bond_handle_frame() here:
slave = bond_slave_get_rcu(skb->dev);
bond = slave->bond; <--- BUG
the slave returned was NULL and accessing slave->bond caused a NULL
pointer dereference.
Looking at the code that unregisters the handler:
void netdev_rx_handler_unregister(struct net_device *dev)
{
ASSERT_RTNL();
RCU_INIT_POINTER(dev->rx_handler, NULL);
RCU_INIT_POINTER(dev->rx_handler_data, NULL);
}
Which is basically:
dev->rx_handler = NULL;
dev->rx_handler_data = NULL;
And looking at __netif_receive_skb() we have:
rx_handler = rcu_dereference(skb->dev->rx_handler);
if (rx_handler) {
if (pt_prev) {
ret = deliver_skb(skb, pt_prev, orig_dev);
pt_prev = NULL;
}
switch (rx_handler(&skb)) {
My question to all of you is, what stops this interrupt from happening
while the bonding module is unloading? What happens if the interrupt
triggers and we have this:
CPU0 CPU1
---- ----
rx_handler = skb->dev->rx_handler
netdev_rx_handler_unregister() {
dev->rx_handler = NULL;
dev->rx_handler_data = NULL;
rx_handler()
bond_handle_frame() {
slave = skb->dev->rx_handler;
bond = slave->bond; <-- NULL pointer dereference!!!
What protection am I missing in the bond release handler that would
prevent the above from happening?
</quoting Steven>
We can fix bug this in two ways. First is adding a test in
bond_handle_frame() and others to check if rx_handler_data is NULL.
A second way is adding a synchronize_net() in
netdev_rx_handler_unregister() to make sure that a rcu protected reader
has the guarantee to see a non NULL rx_handler_data.
The second way is better as it avoids an extra test in fast path.
Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jiri Pirko <jpirko@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/core/dev.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3070,6 +3070,7 @@ int netdev_rx_handler_register(struct ne
if (dev->rx_handler)
return -EBUSY;
+ /* Note: rx_handler_data must be set before rx_handler */
rcu_assign_pointer(dev->rx_handler_data, rx_handler_data);
rcu_assign_pointer(dev->rx_handler, rx_handler);
@@ -3090,6 +3091,11 @@ void netdev_rx_handler_unregister(struct
ASSERT_RTNL();
rcu_assign_pointer(dev->rx_handler, NULL);
+ /* a reader seeing a non NULL rx_handler in a rcu_read_lock()
+ * section has a guarantee to see a non NULL rx_handler_data
+ * as well.
+ */
+ synchronize_net();
rcu_assign_pointer(dev->rx_handler_data, NULL);
}
EXPORT_SYMBOL_GPL(netdev_rx_handler_unregister);
Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are
queue-3.0/8021q-fix-a-potential-use-after-free.patch
queue-3.0/tcp-preserve-ack-clocking-in-tso.patch
queue-3.0/aoe-reserve-enough-headroom-on-skbs.patch
queue-3.0/net-add-a-synchronize_net-in-netdev_rx_handler_unregister.patch
queue-3.0/drivers-net-ethernet-davinci_emac-use-netif_wake_queue-while-restarting-tx-queue.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html