linux-kernel - Re: [PATCH] net/sched: Prevent notify to parent who unsupport class ops

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Message-ID: <51c73a40-fd3d-40d3-b6a1-f0b15ce98239@redhat.com>
Date: Fri, 4 Jul 2025 16:01:53 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Lizhi Xu <lizhi.xu@...driver.com>,
 syzbot+1261670bbdefc5485a06@...kaller.appspotmail.com
Cc: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org,
 jhs@...atatu.com, jiri@...nulli.us, kuba@...nel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 syzkaller-bugs@...glegroups.com, xiyou.wangcong@...il.com
Subject: Re: [PATCH] net/sched: Prevent notify to parent who unsupport class
 ops

On 7/4/25 10:04 AM, Lizhi Xu wrote:
> If the parent qdisc does not support class operations then exit notify.
> 
> In addition, the validity of the cl value is judged before executing the
> notify. Similarly, the notify is exited when the address represented by
> its value is invalid.
> 
> Reported-by: syzbot+1261670bbdefc5485a06@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=1261670bbdefc5485a06
> Tested-by: syzbot+1261670bbdefc5485a06@...kaller.appspotmail.com
> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> ---
>  net/sched/sch_api.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index d8a33486c51..53fd63af14d 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -803,12 +803,13 @@ void qdisc_tree_reduce_backlog(struct Qdisc *sch, int n, int len)
>  			break;
>  		}
>  		cops = sch->ops->cl_ops;
> -		if (notify && cops->qlen_notify) {
> +		if (cops && notify && cops->qlen_notify) {
>  			/* Note that qlen_notify must be idempotent as it may get called
>  			 * multiple times.
>  			 */
>  			cl = cops->find(sch, parentid);
> -			cops->qlen_notify(sch, cl);
> +			if (virt_addr_valid(cl))
> +				cops->qlen_notify(sch, cl);

The above causes build failures in arm64 builds:

  ../net/sched/sch_api.c: In function ‘qdisc_tree_reduce_backlog’:
  ../arch/arm64/include/asm/memory.h:424:66: error: passing argument 1
of ‘virt_to_pfn’ makes pointer from integer without a cast
[-Wint-conversion]
    424 |         __is_lm_address(__addr) &&
pfn_is_map_memory(virt_to_pfn(__addr));      \

/P