net: bridge: remove stale rcu_barrier() in br_multicast_dev_del()

Overview

In the Linux kernel, the following vulnerability has been resolved:

net: bridge: remove stale rcu_barrier() in br_multicast_dev_del()

This rcu_barrier() came from a time call_rcu() calls were used in net/bridge/br_multicast.c.

Now kfree_rcu() is there, we can remove this problematic rcu_barrier() which causes extreme RTNL pressure in many syzbot reports.

INFO: task syz-executor:77945 is blocked on a mutex likely owned by task kworker/u1024:5:36537. task:kworker/u1024:5 state:D stack:24616 pid:36537 tgid:36537 ppid:2 task_flags:0x4208060 flags:0x00080000 last_sleep:612797637337 Workqueue: netns cleanup_net Call Trace: <TASK> [<ffffffff81914eaa>] context_switch+0xf2a/0x1730 kernel/sched/core.c:6483 [<ffffffff81201143>] __schedule+0x1133/0x43a0 kernel/sched/core.c:8411 [<ffffffff8120446b>] __schedule_loop kernel/sched/core.c:8514 [inline] [<ffffffff8120446b>] schedule+0xab/0x260 kernel/sched/core.c:8529 [<ffffffff8121a093>] schedule_timeout+0xc3/0x2b0 kernel/time/sleep_timeout.c:75 [<ffffffff81205347>] do_wait_for_common kernel/sched/completion.c:100 [inline] [<ffffffff81205347>] __wait_for_common kernel/sched/completion.c:121 [inline] [<ffffffff81205347>] wait_for_common kernel/sched/completion.c:132 [inline] [<ffffffff81205347>] wait_for_completion+0x2c7/0x5d0 kernel/sched/completion.c:153 [<ffffffff81b8f27f>] rcu_barrier+0x49f/0x620 kernel/rcu/tree.c:3888 [<ffffffff860091b3>] br_multicast_dev_del+0x303/0x350 net/bridge/br_multicast.c:4459 [<ffffffff85fb5dbc>] br_dev_uninit+0x1c/0x40 net/bridge/br_device.c:157 [<ffffffff8568058c>] unregister_netdevice_many_notify+0x1c1c/0x2300 net/core/dev.c:12599 [<ffffffff8562be43>] ops_exit_rtnl_list net/core/net_namespace.c:187 [inline] [<ffffffff8562be43>] ops_undo_list+0x3d3/0x940 net/core/net_namespace.c:248

Affected

• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < 35f9f11740515a10b084adfb1ce691351f2452ab
• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < 0443f6aac6bf6a91e406273fdda11497cef6ad07
• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < ac0e823a228f94ad9d7a3d876cc07e59a7afb806
• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < f0018acf0b66f93a292667c9a9c2a26c570cf270
• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < 372ee8fbe0f796031c60f676ec90f0788c26523d
• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < 39679927fa7aaf4601119f7234342d1b5d4f6f84
• Linux >= 19e3a9c90c53479fecaa02307bf2db5ab8b3ffe3 < 25ae123db10ba9ab890b56bcdb0a4363aee8529a
• Linux 5.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.