netdev - Re: [PATCH net v4] cls_u32: fix use after free in u32_destroy

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Date:   Tue, 06 Feb 2018 11:32:18 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, shuali@...hat.com, ivecera@...hat.com
Subject: Re: [PATCH net v4] cls_u32: fix use after free in u32_destroy_key()

From: Paolo Abeni <pabeni@...hat.com>
Date: Mon,  5 Feb 2018 22:23:01 +0100

> Li Shuang reported an Oops with cls_u32 due to an use-after-free
> in u32_destroy_key(). The use-after-free can be triggered with:
> 
> dev=lo
> tc qdisc add dev $dev root handle 1: htb default 10
> tc filter add dev $dev parent 1: prio 5 handle 1: protocol ip u32 divisor 256
> tc filter add dev $dev protocol ip parent 1: prio 5 u32 ht 800:: match ip dst\
>  10.0.0.0/8 hashkey mask 0x0000ff00 at 16 link 1:
> tc qdisc del dev $dev root
> 
> Which causes the following kasan splat:
 ...
> The problem is that the htnode is freed before the linked knodes and the
> latter will try to access the first at u32_destroy_key() time.
> This change addresses the issue using the htnode refcnt to guarantee
> the correct free order. While at it also add a RCU annotation,
> to keep sparse happy.
> 
> v1 -> v2: use rtnl_derefence() instead of RCU read locks
> v2 -> v3:
>   - don't check refcnt in u32_destroy_hnode()
>   - cleaned-up u32_destroy() implementation
>   - cleaned-up code comment
> v3 -> v4:
>   - dropped unneeded comment
> 
> Reported-by: Li Shuang <shuali@...hat.com>
> Fixes: c0d378ef1266 ("net_sched: use tcf_queue_work() in u32 filter")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Applied and queued up for -stable, thanks!