]> git.itanic.dy.fi Git - linux-stable/commit
fbdev: fb_pm2fb: Avoid potential divide by zero error
authorLetu Ren <fantasquex@gmail.com>
Thu, 18 Aug 2022 10:44:24 +0000 (18:44 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Mon, 5 Sep 2022 08:23:57 +0000 (10:23 +0200)
commit0f1174f4972ea9fad6becf8881d71adca8e9ca91
treed9d4c43df53577d3e3f976fef58a8c80a9cfe1b0
parent1bea0bbf66001b0c7bf239a4d70eaf47824d3feb
fbdev: fb_pm2fb: Avoid potential divide by zero error

commit 19f953e7435644b81332dd632ba1b2d80b1e37af upstream.

In `do_fb_ioctl()` of fbmem.c, if cmd is FBIOPUT_VSCREENINFO, var will be
copied from user, then go through `fb_set_var()` and
`info->fbops->fb_check_var()` which could may be `pm2fb_check_var()`.
Along the path, `var->pixclock` won't be modified. This function checks
whether reciprocal of `var->pixclock` is too high. If `var->pixclock` is
zero, there will be a divide by zero error. So, it is necessary to check
whether denominator is zero to avoid crash. As this bug is found by
Syzkaller, logs are listed below.

divide error in pm2fb_check_var
Call Trace:
 <TASK>
 fb_set_var+0x367/0xeb0 drivers/video/fbdev/core/fbmem.c:1015
 do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1110
 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1189

Reported-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Letu Ren <fantasquex@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/video/fbdev/pm2fb.c