net_sched: prio: fix a race in prio_tune()

Summary

In the Linux kernel, the following vulnerability has been resolved: net_sched: prio: fix a race in prio_tune() Gerrard Tai reported a race condition in PRIO, whenever SFQ perturb timer fires at the wrong time. The race is as follows: CPU 0 CPU 1 [1]: lock root [2]: qdisc_tree_flush_backlog() [3]: unlock root | | [5]: lock root | [6]: rehash | [7]: qdisc_tree_reduce_backlog() | [4]: qdisc_put() This can be abused to underflow a parent's qlen. Calling qdisc_purge_queue() instead of qdisc_tree_flush_backlog() should fix the race, because all packets will be purged from the qdisc before releasing the lock.

Timeline

1. Jun 20, 2025, 11:21 AM UTCCVE published
2. Oct 15, 2026, 9:47 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 15, 2026, 9:52 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in 53d11560e957d53ee87a0653d258038ce12361b7; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in 4483d8b9127591c60c4eb789d6cab953bc4522a9; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in 20f68e6a9e41693cb0e55e5b9ebbcb40983a4b8f; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in 3aaa7c01cf19d9b9bb64b88b65c3a6fd05da2eb4; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in 46c15c9d0f65c9ba857d63f53264f4b17e8a715f; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in e3f6745006dc9423d2b065b90f191cfa11b1b584; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in 93f9eeb678d4c9c1abf720b3615fa8299a490845; From 7b8e0b6e659983154c8d7e756cdb833d89a3d4d7 · fixed in d35acc1be3480505b5931f17e4ea9b7617fea4d3

• Linux Linux

  5.0

• KernelLinux

  From 5.0.0 · fixed in 5.4.295; From 5.5.0 · fixed in 5.10.239; From 5.11.0 · fixed in 5.15.186; From 5.16.0 · fixed in 6.1.142; From 6.2.0 · fixed in 6.6.94; From 6.7.0 · fixed in 6.12.34; From 6.13.0 · fixed in 6.15.3

References 8