[PATCH 3.16 72/83] net: Fix null de-reference of device refcount

From: Ben Hutchings
Date: Wed Nov 20 2019 - 10:43:22 EST

3.16.78-rc1 review patch. If anyone has any objections, please let me know.


From: Subash Abhinov Kasiviswanathan <subashab@xxxxxxxxxxxxxx>

commit 10cc514f451a0f239aa34f91bc9dc954a9397840 upstream.

In event of failure during register_netdevice, free_netdev is
invoked immediately. free_netdev assumes that all the netdevice
refcounts have been dropped prior to it being called and as a
result frees and clears out the refcount pointer.

However, this is not necessarily true as some of the operations
in the NETDEV_UNREGISTER notifier handlers queue RCU callbacks for
invocation after a grace period. The IPv4 callback in_dev_rcu_put
tries to access the refcount after free_netdev is called which
leads to a null de-reference-

44837.761523: <6> Unable to handle kernel paging request at
virtual address 0000004a88287000
44837.761651: <2> pc : in_dev_finish_destroy+0x4c/0xc8
44837.761654: <2> lr : in_dev_finish_destroy+0x2c/0xc8
44837.762393: <2> Call trace:
44837.762398: <2> in_dev_finish_destroy+0x4c/0xc8
44837.762404: <2> in_dev_rcu_put+0x24/0x30
44837.762412: <2> rcu_nocb_kthread+0x43c/0x468
44837.762418: <2> kthread+0x118/0x128
44837.762424: <2> ret_from_fork+0x10/0x1c

Fix this by waiting for the completion of the call_rcu() in
case of register_netdevice errors.

Fixes: 93ee31f14f6f ("[NET]: Fix free_netdev on register_netdev failure.")
Cc: Sean Tranchetti <stranche@xxxxxxxxxxxxxx>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
net/core/dev.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6278,6 +6278,8 @@ int register_netdevice(struct net_device
ret = notifier_to_errno(ret);
if (ret) {
+ rcu_barrier();
dev->reg_state = NETREG_UNREGISTERED;