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net_sched: Prevent creation of classes with TC_H_ROOT

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[ Upstream commit 0c3057a5a04d07120b3d0ec9c79568fceb9c921e ]

The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination
condition when traversing up the qdisc tree to update parent backlog
counters. However, if a class is created with classid TC_H_ROOT, the
traversal terminates prematurely at this class instead of reaching the
actual root qdisc, causing parent statistics to be incorrectly maintained.
In case of DRR, this could lead to a crash as reported by Mingi Cho.

Prevent the creation of any Qdisc class with classid TC_H_ROOT
(0xFFFFFFFF) across all qdisc types, as suggested by Jamal.

Reported-by: Mingi Cho <mincho@theori.io>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Fixes: 066a3b5b2346 ("[NET_SCHED] sch_api: fix qdisc_tree_decrease_qlen() loop")
Link: https://patch.msgid.link/20250306232355.93864-2-xiyou.wangcong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Cong Wang 2025-03-06 15:23:54 -08:00 committed by Greg Kroah-Hartman
parent 917e520430
commit e5ee00607b
1 changed files with 6 additions and 0 deletions
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6
net/sched/sch_api.c
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@ -2200,6 +2200,12 @@ static int tc_ctl_tclass(struct sk_buff *skb, struct nlmsghdr *n,
return -EOPNOTSUPP;
}
/* Prevent creation of traffic classes with classid TC_H_ROOT */
if (clid == TC_H_ROOT) {
NL_SET_ERR_MSG(extack, "Cannot create traffic class with classid TC_H_ROOT");
return -EINVAL;
}
new_cl = cl;
err = -EOPNOTSUPP;
if (cops->change)