[SRU][F/J/N/O/P][PATCH 0/1] CVE-2025-37797

[Tim Whisonant]

SRU Justification:

[Impact]

net_sched: hfsc: Fix a UAF vulnerability in class handling

This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class
handling. The issue occurs due to a time-of-check/time-of-use condition
in hfsc_change_class() when working with certain child qdiscs like netem
or codel.

The vulnerability works as follows:
1. hfsc_change_class() checks if a class has packets (q.qlen != 0)
2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,
   codel, netem) might drop packets and empty the queue
3. The code continues assuming the queue is still non-empty, adding
   the class to vttree
4. This breaks HFSC scheduler assumptions that only non-empty classes
   are in vttree
5. Later, when the class is destroyed, this can lead to a Use-After-Free

The fix adds a second queue length check after qdisc_peek_len() to verify
the queue wasn't emptied.

[Fix]

Plucky:   applied Focal patch
Oracular: applied Focal patch
Noble:    applied Focal patch
Jammy:    applied Focal patch
Focal:    cherry picked from upstream
Bionic:   patch sent to ESM ML
Xenial:   patch sent to ESM ML
Trusty:   out of scope (medium CVE)

[Test Plan]

Compile and boot tested.

[Where problems could occur]

The change affects the Hierarchical Fair Service Curve network
queuing discipline. Errors may appear as anomolies when using
this queuing discipline.

Cong Wang (1):
  net_sched: hfsc: Fix a UAF vulnerability in class handling

 net/sched/sch_hfsc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

-- 
2.43.0