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?
Helge