Bug 2559547 (CVE-2026-98881)

Summary: CVE-2026-98881 kernel: net: bridge: remove stale rcu_barrier() in br_multicast_dev_del()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's bridge networking subsystem. An obsolete synchronization call during the deletion of bridge multicast devices causes severe lock contention within the networking layer. A local user could exploit this flaw by repeatedly creating and removing network bridge devices, causing kernel tasks to stall and resulting in a Denial of Service (DoS).
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-10-23 11:53:16 UTC 
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
Comment 1 Mauro Matteo Cascella 2026-10-26 11:31:03 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98881.mbox