linux-kernel - Re: [PATCH] net: sched: cls_u32: Avoid memcpy() false-positive warning

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Message-ID: <CAM0EoMnGbS-KHknPU+3gf2CaQO7XtKt-jFRZEZ42ZxAS=3ZzMQ@mail.gmail.com>
Date:   Thu, 29 Sep 2022 06:18:17 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] net: sched: cls_u32: Avoid memcpy() false-positive warning

On Tue, Sep 27, 2022 at 11:37 AM Kees Cook <keescook@...omium.org> wrote:
>
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), use unsafe_memcpy(), as the sizing,
> bounds-checking, and allocation are all very tightly coupled here.
> This silences the false-positive reported by syzbot:
>
>   memcpy: detected field-spanning write (size 80) of single field "&n->sel" at net/sched/cls_u32.c:1043 (size 16)
>
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org
>
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Cong Wang <xiyou.wangcong@...il.com>
> Cc: Jiri Pirko <jiri@...nulli.us>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> Reported-by: syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com
> Link: https://lore.kernel.org/lkml/000000000000a96c0b05e97f0444@google.com/
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal