linux-kernel - [PATCH 3.2 084/153] bridge: check brport attr show in brport

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Date:   Wed, 30 May 2018 11:52:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Xin Long" <lucien.xin@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Xiong Zhou" <xzhou@...hat.com>
Subject: [PATCH 3.2 084/153] bridge: check brport attr show in brport_show

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

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

From: Xin Long <lucien.xin@...il.com>

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@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -196,6 +196,9 @@ 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);
 }