[PATCH 3.16 227/410] bridge: check brport attr show in brport_show

From: Ben Hutchings
Date: Thu Jun 07 2018 - 10:31:05 EST


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

------------------

From: Xin Long <lucien.xin@xxxxxxxxx>

commit 1b12580af1d0677c3c3a19e35bfe5d59b03f737f upstream.

Now br_sysfs_if file flush doesn't have attr show. To read it will
cause kernel panic after users chmod u+r this file.

Xiong found this issue when running the commands:

ip link add br0 type bridge
ip link add type veth
ip link set veth0 master br0
chmod u+r /sys/devices/virtual/net/veth0/brport/flush
timeout 3 cat /sys/devices/virtual/net/veth0/brport/flush

kernel crashed with NULL a pointer dereference call trace.

This patch is to fix it by return -EINVAL when brport_attr->show
is null, just the same as the check for brport_attr->store in
brport_store().

Fixes: 9cf637473c85 ("bridge: add sysfs hook to flush forwarding table")
Reported-by: Xiong Zhou <xzhou@xxxxxxxxxx>
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
net/bridge/br_sysfs_if.c | 3 +++
1 file changed, 3 insertions(+)

--- a/net/bridge/br_sysfs_if.c
+++ b/net/bridge/br_sysfs_if.c
@@ -225,6 +225,9 @@ static ssize_t brport_show(struct kobjec
struct brport_attribute *brport_attr = to_brport_attr(attr);
struct net_bridge_port *p = to_brport(kobj);

+ if (!brport_attr->show)
+ return -EINVAL;
+
return brport_attr->show(p, buf);
}