bridge: fix br_stp_set_bridge_priority race conditions

commit 2dab80a8b486f02222a69daca6859519e05781d9 upstream.

After the ->set() spinlocks were removed br_stp_set_bridge_priority
was left running without any protection when used via sysfs. It can
race with port add/del and could result in use-after-free cases and
corrupted lists. Tested by running port add/del in a loop with stp
enabled while setting priority in a loop, crashes are easily
reproducible.
The spinlocks around sysfs ->set() were removed in commit:
14f98f258f19 ("bridge: range check STP parameters")
There's also a race condition in the netlink priority support that is
fixed by this change, but it was introduced recently and the fixes tag
covers it, just in case it's needed the commit is:
af615762e972 ("bridge: add ageing_time, stp_state, priority over netlink")

Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Fixes: 14f98f258f19 ("bridge: range check STP parameters")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Zefan Li <lizefan@huawei.com>

diff --git a/net/bridge/br_ioctl.c b/net/bridge/br_ioctl.c
index 7222fe1d5460203ad5d1edff1ee5331d49fdb036..ea0e15c7ea17fb63cefcd0b2a7e7efb575ee55b3 100644 (file)
--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -246,9 +246,7 @@ static int old_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
                if (!capable(CAP_NET_ADMIN))
                        return -EPERM;
 
-               spin_lock_bh(&br->lock);
                br_stp_set_bridge_priority(br, args[1]);
-               spin_unlock_bh(&br->lock);
                return 0;
 
        case BRCTL_SET_PORT_PRIORITY:

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 2f100ccef86ff9150e958b99bdb923649d1eb687..23ea15989d55a07bfe9cb363e27f5a9e7c0c9fbd 100644 (file)
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -242,12 +242,13 @@ bool br_stp_recalculate_bridge_id(struct net_bridge *br)
        return true;
 }
 
-/* called under bridge lock */
+/* Acquires and releases bridge lock */
 void br_stp_set_bridge_priority(struct net_bridge *br, u16 newprio)
 {
        struct net_bridge_port *p;
        int wasroot;
 
+       spin_lock_bh(&br->lock);
        wasroot = br_is_root_bridge(br);
 
        list_for_each_entry(p, &br->port_list, list) {
@@ -265,6 +266,7 @@ void br_stp_set_bridge_priority(struct net_bridge *br, u16 newprio)
        br_port_state_selection(br);
        if (br_is_root_bridge(br) && !wasroot)
                br_become_root_bridge(br);
+       spin_unlock_bh(&br->lock);
 }
 
 /* called under bridge lock */