netdev - Re: [PATCH net 2/2] net/sched: sch_frag: fix stack OOB read while fragmenting IPv4 packets

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Date:   Tue, 20 Apr 2021 12:27:19 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Davide Caratti <dcaratti@...hat.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, wenxu <wenxu@...oud.cn>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net 2/2] net/sched: sch_frag: fix stack OOB read while
 fragmenting IPv4 packets

On Mon, Apr 19, 2021 at 8:24 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> when 'act_mirred' tries to fragment IPv4 packets that had been previously
> re-assembled using 'act_ct', splats like the following can be observed on
> kernels built with KASAN:
[...]
> for IPv4 packets, sch_fragment() uses a temporary struct dst_entry. Then,
> in the following call graph:
>
>   ip_do_fragment()
>     ip_skb_dst_mtu()
>       ip_dst_mtu_maybe_forward()
>         ip_mtu_locked()
>
> the pointer to struct dst_entry is used as pointer to struct rtable: this
> turns the access to struct members like rt_mtu_locked into an OOB read in
> the stack. Fix this changing the temporary variable used for IPv4 packets
> in sch_fragment(), similarly to what is done for IPv6 few lines below.
>
> Fixes: c129412f74e9 ("net/sched: sch_frag: add generic packet fragment support.")
> Cc: <stable@...r.kernel.org> # 5.11
> Reported-by: Shuang Li <shuali@...hat.com>
> Signed-off-by: Davide Caratti <dcaratti@...hat.com>

Acked-by: Cong Wang <cong.wang@...edance.com>

Thanks.