On 8/18/22 12:44, Letu Ren wrote: > 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@xxxxxxxxx> > Signed-off-by: Letu Ren <fantasquex@xxxxxxxxx> applied. Thanks! Helge > --- > 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 d3be2c64f1c0..8fd79deb1e2a 100644 > --- a/drivers/video/fbdev/pm2fb.c > +++ b/drivers/video/fbdev/pm2fb.c > @@ -617,6 +617,11 @@ 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));