linux-kernel - Re: [PATCH] proc_sysctl: clamp sizes using table->maxlen

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Date:   Tue, 16 Feb 2021 09:47:28 +0100
From:   Christoph Hellwig <hch@....de>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
Cc:     linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Christoph Hellwig <hch@....de>, Andrey Ignatov <rdna@...com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] proc_sysctl: clamp sizes using table->maxlen

On Mon, Feb 15, 2021 at 09:53:05AM -0500, Alex Xu (Hello71) wrote:
> Since maxlen is already exposed, we can allocate approximately the right
> amount directly, fixing up those drivers which set a bogus maxlen. These
> drivers were located based on those which had copy_x_user replaced in
> 32927393dc1c, on the basis that other drivers either use builtin proc_*
> handlers, or do not access the data pointer. The latter is OK because
> maxlen only needs to be an upper limit.

Please split this into one patch each each subsystem that sets maxlen
to 0 and the actual change to proc_sysctl.c.

How do these maxlen = 0 entries even survive the sysctl_check_table
check?