linux-kernel - Re: [PATCH v3] md: fix an incorrect NULL check in does_sb_need

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Message-ID: <CAPhsuW5qZiE4z0j_+pJbiHQ+zK9oVw3DLgEXdSQ0m=m5ULX1Mw@mail.gmail.com>
Date:   Fri, 8 Apr 2022 09:35:54 -0700
From:   Song Liu <song@...nel.org>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     Xiaomeng Tong <xiam0nd.tong@...il.com>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        linux-raid <linux-raid@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] md: fix an incorrect NULL check in does_sb_need_changing

On Fri, Apr 8, 2022 at 5:23 AM Goldwyn Rodrigues <rgoldwyn@...e.de> wrote:
>
> On 16:37 08/04, Xiaomeng Tong wrote:
> > The bug is here:
> >       if (!rdev)
> >
> > The list iterator value 'rdev' will *always* be set and non-NULL
> > by rdev_for_each(), so it is incorrect to assume that the iterator
> > value will be NULL if the list is empty or no element found.
> > Otherwise it will bypass the NULL check and lead to invalid memory
> > access passing the check.
> >
> > To fix the bug, use a new variable 'iter' as the list iterator,
> > while using the original variable 'rdev' as a dedicated pointer to
> > point to the found element.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: 2aa82191ac36 ("md-cluster: Perform a lazy update")
> > Acked-by: Guoqing Jiang <guoqing.jiang@...ux.dev>
> > Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
>
> Also safeguards from reading sb from a faulty device if all devices are
> faulty.
>
> Acked-by: Goldwyn Rodrigues <rgoldwyn@...e.com>

Applied to md-next. Thanks!