linux-kernel - Re: [PATCH] net: sched: sch_teql: fix null-pointer dereference

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Message-ID: <0c385039-3780-b5d0-ba36-c1c51da9bc08@gmail.com>
Date:   Thu, 8 Apr 2021 17:26:00 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sched: sch_teql: fix null-pointer dereference



On 4/8/21 5:14 PM, Pavel Tikhomirov wrote:
> Reproduce:
> 
>   modprobe sch_teql
>   tc qdisc add dev teql0 root teql0
> 
> This leads to (for instance in Centos 7 VM) OOPS:
> 
>
> 
> Null pointer dereference happens on master->slaves dereference in
> teql_destroy() as master is null-pointer.
> 
> When qdisc_create() calls teql_qdisc_init() it imediately fails after
> check "if (m->dev == dev)" because both devices are teql0, and it does
> not set qdisc_priv(sch)->m leaving it zero on error path, then
> qdisc_create() imediately calls teql_destroy() which does not expect
> zero master pointer and we get OOPS.
> 
> Signed-off-by: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
> ---

This makes sense, thanks !

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

I would think bug origin is 

Fixes: 87b60cfacf9f ("net_sched: fix error recovery at qdisc creation")

Can you confirm you have this backported to 3.10.0-1062.7.1.el7.x86_64 ?