On Wed, Nov 23, 2022 at 07:34:39AM +0100, Ulrich Hecht wrote:
On 09/13/2022 4:07 PM CEST Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
From: Letu Ren fantasquex@gmail.com
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 Signed-off-by: Sasha Levin sashal@kernel.org
drivers/video/fbdev/pm2fb.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c index 9b32b9fc44a5c..50b569d047b10 100644 --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -619,6 +619,11 @@ static int pm2fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info) return -EINVAL; }
- if (!var->pixclock) {
DPRINTK("pixclock is zero\n");return -EINVAL;- }
- if (PICOS2KHZ(var->pixclock) > PM2_MAX_PIXCLOCK) { DPRINTK("pixclock too high (%ldKHz)\n", PICOS2KHZ(var->pixclock));
-- 2.35.1
This is a duplicate, the same patch has already been applied in 4.9.327 (0f1174f4972ea9fad6becf8881d71adca8e9ca91), so the above snippet of code is now in there twice.
Doesn't make a difference in functionality in this case, I just happened to notice it when reviewing backports from 4.9 for the CIP 4.4-stable tree.
Good catch, want to send a revert for this to fix it up?
thanks,
greg k-h