[SRU][F/J/O][PATCH 0/1] CVE-2025-21703

[Tim Whisonant]

[Impact]

netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()

qdisc_tree_reduce_backlog() notifies parent qdisc only if child
qdisc becomes empty, therefore we need to reduce the backlog of the
child qdisc before calling it. Otherwise it would miss the opportunity
to call cops->qlen_notify(), in the case of DRR, it resulted in UAF
since DRR uses ->qlen_notify() to maintain its active list.

[Cherry Pick]

Cherry picked from upstream.

[Fix]

Oracular: cherry picked from upstream
Noble:    not affected
Jammy:    cherry picked from upstream
Focal:    cherry picked from upstream
Bionic:   not affected
Xenial:   not affected
Trusty:   not affected

[Test Plan]

Compile and boot tested.

[Where problems could occur]

The change affects the core network logic. Problems might manifest as
anomalies in the queuing discipline backlog processing.

Cong Wang (1):
  netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()

 net/sched/sch_netem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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2.43.0