net_sched: red: fix a race in __red_change()

Summary

In the Linux kernel, the following vulnerability has been resolved: net_sched: red: fix a race in __red_change() Gerrard Tai reported a race condition in RED, 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. Jul 3, 2025, 8:35 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 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in 2790c4ec481be45a80948d059cd7c9a06bc37493; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in a1bf6a4e9264a685b0e642994031f9c5aad72414; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in 110a47efcf23438ff8d31dbd9c854fae2a48bf98; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in f569984417a4e12c67366e69bdcb752970de921d; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in 2a71924ca4af59ffc00f0444732b6cd54b153d0e; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in 4b755305b2b0618e857fdadb499365b5f2e478d1; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in 444ad445df5496a785705019268a8a84b84484bb; From 0c8d13ac96070000da33f394f45e9c19638483c5 · fixed in 85a3e0ede38450ea3053b8c45d28cf55208409b8

• 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