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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: 7582f5b70f ("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>
This commit is contained in:
Vladimir Oltean 2020-09-22 01:07:09 +03:00 committed by David S. Miller
parent 47cec3f68c
commit 99f62a7460
1 changed files with 17 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
net/bridge/br_vlan.c
View File

@ -1288,11 +1288,13 @@ void br_vlan_get_stats(const struct net_bridge_vlan *v,
}
}
static int __br_vlan_get_pvid(const struct net_device *dev,
struct net_bridge_port *p, u16 *p_pvid)
int br_vlan_get_pvid(const struct net_device *dev, u16 *p_pvid)
{
struct net_bridge_vlan_group *vg;
struct net_bridge_port *p;
ASSERT_RTNL();
p = br_port_get_check_rtnl(dev);
if (p)
vg = nbp_vlan_group(p);
else if (netif_is_bridge_master(dev))
@ -1303,18 +1305,23 @@ static int __br_vlan_get_pvid(const struct net_device *dev,
*p_pvid = br_get_pvid(vg);
return 0;
}
int br_vlan_get_pvid(const struct net_device *dev, u16 *p_pvid)
{
ASSERT_RTNL();
return __br_vlan_get_pvid(dev, br_port_get_check_rtnl(dev), p_pvid);
}
EXPORT_SYMBOL_GPL(br_vlan_get_pvid);
int br_vlan_get_pvid_rcu(const struct net_device *dev, u16 *p_pvid)
{
return __br_vlan_get_pvid(dev, br_port_get_check_rcu(dev), p_pvid);
struct net_bridge_vlan_group *vg;
struct net_bridge_port *p;
p = br_port_get_check_rcu(dev);
if (p)
vg = nbp_vlan_group_rcu(p);
else if (netif_is_bridge_master(dev))
vg = br_vlan_group_rcu(netdev_priv(dev));
else
return -EINVAL;
*p_pvid = br_get_pvid(vg);
return 0;
}
EXPORT_SYMBOL_GPL(br_vlan_get_pvid_rcu);