linux-kernel - Re: [PATCH net-next] wlcore: fix overlapping snprintf arguments in debugfs

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Message-ID: <8735w2nwxm.fsf@codeaurora.org>
Date:   Wed, 07 Apr 2021 14:41:57 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Luciano Coelho <coelho@...com>, Arik Nemtsov <arik@...ery.com>,
        Arnd Bergmann <arnd@...db.de>,
        Lee Jones <lee.jones@...aro.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] wlcore: fix overlapping snprintf arguments in debugfs

Arnd Bergmann <arnd@...nel.org> writes:

> From: Arnd Bergmann <arnd@...db.de>
>
> gcc complains about undefined behavior in calling snprintf()
> with the same buffer as input and output:
>
> drivers/net/wireless/ti/wl18xx/debugfs.c: In function
> 'diversity_num_of_packets_per_ant_read':
> drivers/net/wireless/ti/wl18xx/../wlcore/debugfs.h:86:3: error:
> 'snprintf' argument 4 overlaps destination object 'buf'
> [-Werror=restrict]
>    86 |   snprintf(buf, sizeof(buf), "%s[%d] = %d\n",  \
>       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    87 |     buf, i, stats->sub.name[i]);   \
>       |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/wireless/ti/wl18xx/debugfs.c:24:2: note: in expansion of
> macro 'DEBUGFS_FWSTATS_FILE_ARRAY'
>    24 |  DEBUGFS_FWSTATS_FILE_ARRAY(a, b, c, wl18xx_acx_statistics)
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/wireless/ti/wl18xx/debugfs.c:159:1: note: in expansion of macro 'WL18XX_DEBUGFS_FWSTATS_FILE_ARRAY'
>   159 | WL18XX_DEBUGFS_FWSTATS_FILE_ARRAY(diversity, num_of_packets_per_ant,
>
> There are probably other ways of handling the debugfs file, without
> using on-stack buffers, but a simple workaround here is to remember the
> current position in the buffer and just keep printing in there.
>
> Fixes: bcca1bbdd412 ("wlcore: add debugfs macro to help print fw statistics arrays")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/net/wireless/ti/wlcore/boot.c    | 13 ++++++++-----
>  drivers/net/wireless/ti/wlcore/debugfs.h |  7 ++++---

This should go to wireless-drivers-next, not net-next.

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