From: George Kennedy george.kennedy@oracle.com
[ 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 --- 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 e4ce5667b125..1b0a58f96af2 100644 --- a/drivers/video/fbdev/cirrusfb.c +++ b/drivers/video/fbdev/cirrusfb.c @@ -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; @@ -479,9 +479,7 @@ 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; @@ -489,11 +487,13 @@ 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