From 5c6f402bdcf9e7239c6bc7087eda71ac99b31379 Mon Sep 17 00:00:00 2001
From: George Kennedy <george.kennedy@oracle.com>
Date: Wed, 27 Oct 2021 15:30:13 -0500
Subject: [PATCH] video: fbdev: cirrusfb: check pixclock to avoid divide by zero
Git-commit: 5c6f402bdcf9e7239c6bc7087eda71ac99b31379
Patch-mainline: v5.18-rc1
References: git-fixes
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>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/video/fbdev/cirrusfb.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
index 93802abbbc72..3d47c347b897 100644
--- a/drivers/video/fbdev/cirrusfb.c
+++ b/drivers/video/fbdev/cirrusfb.c
@@ -469,7 +469,7 @@ 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;
@@ -478,9 +478,7 @@ 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;
@@ -488,11 +486,13 @@ static int cirrusfb_check_pixclock(const struct fb_var_screeninfo *var,
/* 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
--
2.31.1