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Subject[PATCH 4.4 18/36] bridge: check brport attr show in brport_show
4.4-stable review patch.  If anyone has any objections, please let me know.


From: Xin Long <>

[ Upstream commit 1b12580af1d0677c3c3a19e35bfe5d59b03f737f ]

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

Fixes: 9cf637473c85 ("bridge: add sysfs hook to flush forwarding table")
Reported-by: Xiong Zhou <>
Signed-off-by: Xin Long <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
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
@@ -229,6 +229,9 @@ 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);

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