linux-kernel - Re: [PATCH 00/99] fbdev: Fix memory leak in option parsing

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Date:   Tue, 7 Mar 2023 08:53:39 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     deller@....de, paulus@...ba.org, benh@...nel.crashing.org,
        linux@...linux.org.uk, pjones@...hat.com, timur@...nel.org,
        adaplas@...il.com, s.hauer@...gutronix.de, shawnguo@...nel.org,
        mbroemme@...mpq.org, thomas@...ischhofer.net,
        James.Bottomley@...senpartnership.com, spock@...too.org,
        sudipm.mukherjee@...il.com, teddy.wang@...iconmotion.com,
        corbet@....net, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/99] fbdev: Fix memory leak in option parsing

Hi Thomas,

On Mon, Mar 6, 2023 at 5:00 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
> Introduce struct option_iter and helpers to parse command-line
> options with comma-separated key-value pairs. Then convert fbdev
> drivers to the new interface. Fixes a memory leak in the parsing of
> the video= option.
>
> Before commit 73ce73c30ba9 ("fbdev: Transfer video= option strings to
> caller; clarify ownership"), a call to fb_get_options() either
> returned an internal string or a duplicated string; hence ownership of
> the string's memory buffer was not well defined, but depended on how
> users specified the video= option on the kernel command line. For
> global settings, the caller owned the returned memory and for per-driver
> settings, fb_get_options() owned the memory. As calling drivers were
> unable to detect the case, the memory was leaked.
>
> Commit 73ce73c30ba9 ("fbdev: Transfer video= option strings to caller;
> clarify ownership") changed sematics to caller-owned strings. Drivers
> still leaked the memory, but at least ownership was clear.
>
> This patchset fixes the memory leak and changes string ownership back
> to fb_get_options(). Patch 1 introduces struct option_iter and a few
> helpers. The interface takes an option string, such as video=, in the
> common form value1,key2:value2,value3 etc and returns the individial
> comma-separated pairs. Various modules use this pattern, so the code
> is located under lib/.
>
> Patches 2 to 98 go through fbdev drivers and convert them to the new
> interface. This often requires a number of cleanups. A driver would
> typically refer to the option string's video mode. Such strings are now
> copied to driver-allocated memory so that drivers don't refer directly
> to the option string's memory. The option iterator then replaces manual
> parsing loops based on strsep(",").

Thanks for your series!

Unfortunately I cannot say I'm thrilled about this: you are replacing
a single small dynamic memory leak by 36 larger static memory leaks.
Am I missing something?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds