[SRU][J/N/O/P][PATCH 0/1] CVE-2025-37890

[Ian Whitfield]

[Impact]

net_sched: hfsc: Fix a UAF vulnerability in class

As described in Gerrard's report [1], we have a UAF case when an hfsc class
has a netem child qdisc. The crux of the issue is that hfsc is assuming
that checking for cl->qdisc->q.qlen == 0 guarantees that it hasn't inserted
the class in the vttree or eltree (which is not true for the netem
duplicate case).

This patch checks the n_active class variable to make sure that the code
won't insert the class in the vttree or eltree twice, catering for the
reentrant case.

[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/

[Backport]

The patch applied cleanly.

[Fix]

Plucky:   cherry pick
Oracular: cherry pick
Noble:    cherry pick
Jammy:    cherry pick
Focal:    sent to ESM ML
Bionic:   not affected
Xenial:   not affected
Trusty:   not affected

[Test Case]

Compile and boot tested.

[Where problems could occur]

This fix affects those who use a Hierarchical Fair Service Curve (HFSC) network
scheduler queue discipline (qdisc) with a child Network Emulator (netem) qdisc.
An issue with this fix would be visible to the user as a use-after-free which
could read private information or crash the kernel.

Victor Nogueira (1):
  net_sched: hfsc: Fix a UAF vulnerability in class with netem as child
    qdisc

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

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2.43.0