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Revision 99f62a746066fa436aa15d4606a538569540db08 authored by Vladimir Oltean on 21 September 2020, 22:07:09 UTC, committed by David S. Miller on 22 September 2020, 00:37:44 UTC 
net: bridge: br_vlan_get_pvid_rcu() should dereference the VLAN group under RCU
 
When calling the RCU brother of br_vlan_get_pvid(), lockdep warns:

=============================
WARNING: suspicious RCU usage
5.9.0-rc3-01631-g13c17acb8e38-dirty #814 Not tainted
-----------------------------
net/bridge/br_private.h:1054 suspicious rcu_dereference_protected() usage!

Call trace:
 lockdep_rcu_suspicious+0xd4/0xf8
 __br_vlan_get_pvid+0xc0/0x100
 br_vlan_get_pvid_rcu+0x78/0x108

The warning is because br_vlan_get_pvid_rcu() calls nbp_vlan_group()
which calls rtnl_dereference() instead of rcu_dereference(). In turn,
rtnl_dereference() calls rcu_dereference_protected() which assumes
operation under an RCU write-side critical section, which obviously is
not the case here. So, when the incorrect primitive is used to access
the RCU-protected VLAN group pointer, READ_ONCE() is not used, which may
cause various unexpected problems.

I'm sad to say that br_vlan_get_pvid() and br_vlan_get_pvid_rcu() cannot
share the same implementation. So fix the bug by splitting the 2
functions, and making br_vlan_get_pvid_rcu() retrieve the VLAN groups
under proper locking annotations.

Fixes: 7582f5b70f9a ("bridge: add br_vlan_get_pvid_rcu()")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 parent 47cec3f
Raw File
test_module.c 
// SPDX-License-Identifier: GPL-2.0-only
/*
 * This module emits "Hello, world" on printk when loaded.
 *
 * It is designed to be used for basic evaluation of the module loading
 * subsystem (for example when validating module signing/verification). It
 * lacks any extra dependencies, and will not normally be loaded by the
 * system unless explicitly requested by name.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/init.h>
#include <linux/module.h>
#include <linux/printk.h>

static int __init test_module_init(void)
{
	pr_warn("Hello, world\n");

	return 0;
}

module_init(test_module_init);

static void __exit test_module_exit(void)
{
	pr_warn("Goodbye\n");
}

module_exit(test_module_exit);

MODULE_AUTHOR("Kees Cook <keescook@chromium.org>");
MODULE_LICENSE("GPL");
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