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

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Message-ID: <a5e758d6-ccc8-643c-1409-7ce0d1bcba1f@virtuozzo.com>
Date:   Thu, 8 Apr 2021 18:51:46 +0300
From:   Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To:     Eric Dumazet <eric.dumazet@...il.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 6:26 PM, Eric Dumazet wrote:
> 
> 
> 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>

Thanks!

> 
> 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 ?
> 

According to our source copy it looks backported to 1062.7.1, please see:
https://src.openvz.org/projects/OVZ/repos/vzkernel/browse/net/sched/sch_api.c?at=refs%2Ftags%2Frh7-3.10.0-1062.7.1.el7#1167

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.