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CVE PROGRAM SOURCE RECORD7.8 High

CVE-2025-38350

net/sched: Always pass notifications when child class becomes empty

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Status
Published
Published
Updated
Assigning organization
Linux

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: Always pass notifications when child class becomes empty Certain classful qdiscs may invoke their classes' dequeue handler on an enqueue operation. This may unexpectedly empty the child qdisc and thus make an in-flight class passive via qlen_notify(). Most qdiscs do not expect such behaviour at this point in time and may re-activate the class eventually anyways which will lead to a use-after-free. The referenced fix commit attempted to fix this behavior for the HFSC case by moving the backlog accounting around, though this turned out to be incomplete since the parent's parent may run into the issue too. The following reproducer demonstrates this use-after-free: tc qdisc add dev lo root handle 1: drr tc filter add dev lo parent 1: basic classid 1:1 tc class add dev lo parent 1: classid 1:1 drr tc qdisc add dev lo parent 1:1 handle 2: hfsc def 1 tc class add dev lo parent 2: classid 2:1 hfsc rt m1 8 d 1 m2 0 tc qdisc add dev lo parent 2:1 handle 3: netem tc qdisc add dev lo parent 3:1 handle 4: blackhole echo 1 | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888 tc class delete dev lo classid 1:1 echo 1 | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888 Since backlog accounting issues leading to a use-after-frees on stale class pointers is a recurring pattern at this point, this patch takes a different approach. Instead of trying to fix the accounting, the patch ensures that qdisc_tree_reduce_backlog always calls qlen_notify when the child qdisc is empty. This solves the problem because deletion of qdiscs always involves a call to qdisc_reset() and / or qdisc_purge_queue() which ultimately resets its qlen to 0 thus causing the following qdisc_tree_reduce_backlog() to report to the parent. Note that this may call qlen_notify on passive classes multiple times. This is not a problem after the recent patch series that made all the classful qdiscs qlen_notify() handlers idempotent.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • 1034e3310752e8675e313f7271b348914008719a to < 3b290923ad2b23596208c1e29520badef4356a43affected
  • f9f593e34d2fb67644372c8f7b033bdc622ad228 to < e9921b57dca05ac5f4fa1fa8e993d4f0ee52e2b7affected
  • 89c301e929a0db14ebd94b4d97764ce1d6981653 to < e269f29e9395527bc00c213c6b15da04ebb35070affected
  • f1dde3eb17dc1b8bd07aed00004b1e05fc87a3d4 to < 7874c9c132e906a52a187d045995b115973c93fbaffected
  • 93c276942e75de0e5bc91576300d292e968f5a02 to < f680a4643c6f71e758d8fe0431a958e9a6a4f59daffected
  • 49b21795b8e5654a7df3d910a12e1060da4c04cf to < a553afd91f55ff39b1e8a1c4989a29394c9e0472affected
  • 3f981138109f63232a5fb7165938d4c945cc1b9d to < a44acdd9e84a211989ff4b9b92bf3545d8456ad5affected
  • 3f981138109f63232a5fb7165938d4c945cc1b9d to < 103406b38c600fec1fe375a77b27d87e314aea09affected
  • 3f3a22eebbc32b4fa8ce9c1d5f9db214b45b9335affected
  • 5.4.294 to < 5.4.296affected
  • 5.10.238 to < 5.10.240affected
  • 5.15.185 to < 5.15.187affected
  • 6.1.141 to < 6.1.144affected
  • 6.6.93 to < 6.6.97affected
  • 6.12.31 to < 6.12.37affected
  • 6.14.9 to < 6.15affected

Linux Linux

Default version status: affected

  • 6.15affected
  • 0 to < 6.15unaffected
  • 5.4.296 to ≤ 5.4.*unaffected
  • 5.10.240 to ≤ 5.10.*unaffected
  • 5.15.187 to ≤ 5.15.*unaffected
  • 6.1.144 to ≤ 6.1.*unaffected
  • 6.6.97 to ≤ 6.6.*unaffected
  • 6.12.37 to ≤ 6.12.*unaffected
  • 6.15.6 to ≤ 6.15.*unaffected
  • 6.16 to ≤ *unaffected

References