linux-kernel - Re: [PATCH] f2fs: fix dereference of stale list iterator after loop body

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Date:   Tue, 12 Apr 2022 17:49:17 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jakob Koschel <jakobkoschel@...il.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Yunlei He <heyunlei@...wei.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH] f2fs: fix dereference of stale list iterator after loop
 body

On 2022/4/1 6:34, Jakob Koschel wrote:
> The list iterator variable will be a bogus pointer if no break was hit.
> Dereferencing it (cur->page in this case) could load an out-of-bounds/undefined
> value making it unsafe to use that in the comparision to determine if the
> specific element was found.
> 
> Since 'cur->page' *can* be out-ouf-bounds it cannot be guaranteed that
> by chance (or intention of an attacker) it matches the value of 'page'
> even though the correct element was not found.
> 
> This is fixed by using a separate list iterator variable for the loop
> and only setting the original variable if a suitable element was found.
> Then determing if the element was found is simply checking if the
> variable is set.
> 
> Fixes: 8c242db9b8c0 ("f2fs: fix stale ATOMIC_WRITTEN_PAGE private pointer")
> Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,