On Friday 08 April 2022 03:58:10 Zheyu Ma wrote: > On Fri, Apr 8, 2022 at 3:50 AM Helge Deller <deller@xxxxxx> wrote: > > > > On 4/4/22 10:47, Zheyu Ma wrote: > > > The userspace program could pass any values to the driver through > > > ioctl() interface. If the driver doesn't check the value of 'pixclock', > > > it may cause divide error. > > > > > > Fix this by checking whether 'pixclock' is zero in the function > > > i740fb_check_var(). > > > > > > The following log reveals it: > > > > > > divide error: 0000 [#1] PREEMPT SMP KASAN PTI > > > RIP: 0010:i740fb_decode_var drivers/video/fbdev/i740fb.c:444 [inline] > > > RIP: 0010:i740fb_set_par+0x272f/0x3bb0 drivers/video/fbdev/i740fb.c:739 > > > Call Trace: > > > fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1036 > > > do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1112 > > > fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1191 > > > vfs_ioctl fs/ioctl.c:51 [inline] > > > __do_sys_ioctl fs/ioctl.c:874 [inline] > > > > > > Signed-off-by: Zheyu Ma <zheyuma97@xxxxxxxxx> > > > > Hello Zheyu, > > > > I've applied the patches #2-#7 of this series, but left > > out this specific patch (for now). > > As discussed on the mailing list we can try to come up with a > > better fix (to round up the pixclock when it's invalid). > > If not, I will apply this one later. > > I'm also looking forward to a more appropriate patch for this driver! I was not able to reproduce it at first but finally found it: the monitor must be unplugged. If a valid EDID is present, fb_validate_mode() call in i740fb_check_var() will refuse zero pixclock. Haven't found any obvious way to correct zero pixclock value. Most other drivers simply return -EINVAL. > Thanks, > Zheyu Ma > -- Ondrej Zary
