On 4/6/22 03:24, Zheyu Ma wrote:
On Wed, Apr 6, 2022 at 2:23 AM Helge Deller deller@gmx.de wrote:
On 4/5/22 19:46, Ondrej Zary wrote:
On Tuesday 05 April 2022 08:33:57 Helge Deller wrote:
Hello Geert,
On 4/4/22 13:46, Geert Uytterhoeven wrote:
Hi Helge,
On Sun, Apr 3, 2022 at 5:41 PM Helge Deller deller@gmx.de wrote:
On 4/3/22 13:26, Zheyu Ma wrote: > I found a bug in the function i740fb_set_par().
Nice catch!
> When the user calls the ioctl system call without setting the value to > 'var->pixclock', the driver will throw a divide error. > > This bug occurs because the driver uses the value of 'var->pixclock' > without checking it, as the following code snippet show: > > if ((1000000 / var->pixclock) > DACSPEED8) { > dev_err(info->device, "requested pixclock %i MHz out of range > (max. %i MHz at 8bpp)\n", > 1000000 / var->pixclock, DACSPEED8); > return -EINVAL;x > } > > We can fix this by checking the value of 'var->pixclock' in the > function i740fb_check_var() similar to commit > b36b242d4b8ea178f7fd038965e3cac7f30c3f09, or we should set the lowest > supported value when this field is zero. > I have no idea about which solution is better.
Me neither. I think a solution like commit b36b242d4b8ea178f7fd038965e3cac7f30c3f09 is sufficient.
Note that i740fb_set_par() is called in i740fb_resume() as well. Since this doesn't comes form userspace I think adding a check for the return value there isn't necessary.
Would you mind sending a patch like b36b242d4b8ea178f7fd038965e3cac7f30c3f09 ?
When passed an invalid value, .check_var() is supposed to round up the invalid to a valid value, if possible.
I don't disagree. The main problem probably is: what is the next valid value? This needs to be analyzed on a per-driver base and ideally tested. Right now a division-by-zero is tiggered which is probably more worse.
I still have an i740 card so I can test it.
Good. Someone wants to come up with a proposed patch?
I have submitted patches for the i740fb driver and other drivers which have similar bugs as follows: https://lore.kernel.org/all/20220404084723.79089-1-zheyuma97@gmail.com/
Yes, I know. But Ondrej offered to test a patch which would round an invalid pixclock up instead of just returning EINVAL (which is what your patch does). So, if someone comes up with such a patch it'd be the preferred solution.
Helge