From: Victor Nogueira <victor@mojatatu.com> mainline inclusion from mainline-v6.15-rc5 commit 141d34391abbb315d68556b7c67ad97885407547 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IC8Y28 CVE: CVE-2025-37890 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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-... Fixes: 37d9cf1a3ce3 ("sched: Fix detection of empty queues in child qdiscs") Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Victor Nogueira <victor@mojatatu.com> Link: https://patch.msgid.link/20250425220710.3964791-3-victor@mojatatu.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com> --- net/sched/sch_hfsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c index 466b0692ac1e..5d9cccfac4a1 100644 --- a/net/sched/sch_hfsc.c +++ b/net/sched/sch_hfsc.c @@ -1570,7 +1570,7 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free) return err; } - if (first) { + if (first && !cl->cl_nactive) { if (cl->cl_flags & HFSC_RSC) init_ed(cl, len); if (cl->cl_flags & HFSC_FSC) -- 2.25.1