linux-kernel - [media] cx25821: Is there a potential buffer-underflow in cx25821-core.c?

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Date:   Thu, 12 Aug 2021 12:21:35 +0800
From:   Tuo Li <islituo@...il.com>
To:     mchehab@...nel.org, hverkuil-cisco@...all.nl,
        christophe.jaillet@...adoo.fr, tglx@...utronix.de
Cc:     linux-media@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        "baijiaju1990@...il.com" <baijiaju1990@...il.com>
Subject: [media] cx25821: Is there a potential buffer-underflow in
 cx25821-core.c?

Hello,

Our static analysis tool reports a possible buffer-underflow in 
cx25821-core.c in Linux 5.14.0-rc3:

The variable channel_select is checked in:
761:    if (channel_select <= 7 && channel_select >= 0)

This indicates that channel_select can be negative.
If so, a buffer-underflow will occur:
765:    dev->channels[channel_select].pixel_formats = format;

However, we checked this report manually, and found that the only call 
site is in cx25821-video.c:
394:    cx25821_set_pixel_format(dev, SRAM_CH00, pix_format);

And SRAM_CH00 is not negative.

I am not sure whether this negatvie-check is redundant or there is a 
potential buffer-underflow.
Any feedback would be appreciated, thanks!

Reported-by: TOTE Robot <oslab@...nghua.edu.cn>

Best wishes,
Tuo Li