From: Eric Dumazet <edumazet@google.com> stable inclusion from stable-v6.6.94 commit 2a71924ca4af59ffc00f0444732b6cd54b153d0e category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/ICJT90 CVE: CVE-2025-38108 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 85a3e0ede38450ea3053b8c45d28cf55208409b8 ] Gerrard Tai reported a race condition in RED, whenever SFQ perturb timer fires at the wrong time. The race is as follows: CPU 0 CPU 1 [1]: lock root [2]: qdisc_tree_flush_backlog() [3]: unlock root | | [5]: lock root | [6]: rehash | [7]: qdisc_tree_reduce_backlog() | [4]: qdisc_put() This can be abused to underflow a parent's qlen. Calling qdisc_purge_queue() instead of qdisc_tree_flush_backlog() should fix the race, because all packets will be purged from the qdisc before releasing the lock. Fixes: 0c8d13ac9607 ("net: sched: red: delay destroying child qdisc on replace") Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg> Suggested-by: Gerrard Tai <gerrard.tai@starlabs.sg> Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20250611111515.1983366-3-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Luo Gengkun <luogengkun2@huawei.com> --- net/sched/sch_red.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/sch_red.c b/net/sched/sch_red.c index 16277b6a0238..3c6b4460cf2c 100644 --- a/net/sched/sch_red.c +++ b/net/sched/sch_red.c @@ -283,7 +283,7 @@ static int __red_change(struct Qdisc *sch, struct nlattr **tb, q->userbits = userbits; q->limit = ctl->limit; if (child) { - qdisc_tree_flush_backlog(q->qdisc); + qdisc_purge_queue(q->qdisc); old_child = q->qdisc; q->qdisc = child; } -- 2.34.1