Skip to content

Commit

Permalink
video: fbdev: cirrusfb: check pixclock to avoid divide by zero
Browse files Browse the repository at this point in the history
[ Upstream commit 5c6f402bdcf9e7239c6bc7087eda71ac99b31379 ]

Do a sanity check on pixclock value to avoid divide by zero.

If the pixclock value is zero, the cirrusfb driver will round up
pixclock to get the derived frequency as close to maxclock as
possible.

Syzkaller reported a divide error in cirrusfb_check_pixclock.

divide error: 0000 [#1] SMP KASAN PTI
CPU: 0 PID: 14938 Comm: cirrusfb_test Not tainted 5.15.0-rc6 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2
RIP: 0010:cirrusfb_check_var+0x6f1/0x1260

Call Trace:
 fb_set_var+0x398/0xf90
 do_fb_ioctl+0x4b8/0x6f0
 fb_ioctl+0xeb/0x130
 __x64_sys_ioctl+0x19d/0x220
 do_syscall_64+0x3a/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Signed-off-by: George Kennedy <george.kennedy@oracle.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
  • Loading branch information
gkennedy12 authored and gregkh committed Apr 20, 2022
1 parent 944db00 commit 1d3fb46
Showing 1 changed file with 8 additions and 8 deletions.
16 changes: 8 additions & 8 deletions drivers/video/fbdev/cirrusfb.c
Original file line number Diff line number Diff line change
Expand Up @@ -470,7 +470,7 @@ static int cirrusfb_check_mclk(struct fb_info *info, long freq)
return 0;
}

static int cirrusfb_check_pixclock(const struct fb_var_screeninfo *var,
static int cirrusfb_check_pixclock(struct fb_var_screeninfo *var,
struct fb_info *info)
{
long freq;
Expand All @@ -479,21 +479,21 @@ static int cirrusfb_check_pixclock(const struct fb_var_screeninfo *var,
unsigned maxclockidx = var->bits_per_pixel >> 3;

/* convert from ps to kHz */
freq = PICOS2KHZ(var->pixclock);

dev_dbg(info->device, "desired pixclock: %ld kHz\n", freq);
freq = PICOS2KHZ(var->pixclock ? : 1);

maxclock = cirrusfb_board_info[cinfo->btype].maxclock[maxclockidx];
cinfo->multiplexing = 0;

/* If the frequency is greater than we can support, we might be able
* to use multiplexing for the video mode */
if (freq > maxclock) {
dev_err(info->device,
"Frequency greater than maxclock (%ld kHz)\n",
maxclock);
return -EINVAL;
var->pixclock = KHZ2PICOS(maxclock);

while ((freq = PICOS2KHZ(var->pixclock)) > maxclock)
var->pixclock++;
}
dev_dbg(info->device, "desired pixclock: %ld kHz\n", freq);

/*
* Additional constraint: 8bpp uses DAC clock doubling to allow maximum
* pixel clock
Expand Down

0 comments on commit 1d3fb46

Please sign in to comment.