Messages in this thread Patch in this message | | | Date | Mon, 13 Dec 2021 10:29:08 -0500 | From | George Kennedy <> | Subject | [PATCH v2 RESEND 2] video: fbdev: cirrusfb: check pixclock to avoid divide by zero |
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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
Cc: <stable@vger.kernel.org> # 5.4.y Reported-by: syzkaller <syzkaller@googlegroups.com> Signed-off-by: George Kennedy<george.kennedy@oracle.com> Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org> --- Hi Andrew, can you pick this patch up? Some of the fbdev drivers have maintainers but the cirrusfb.c is basically orphaned. I sent this patch in Oct and again in Dec and no one picked it up. Geert has reviewed it. Obviously the original code just crashed so this shouldn't be controversial.
v2: Geert says that instead of just returning an error, this is supposed to find a valid pixclock and use that.
RESEND: Added the Reviewed by: and Cc: <stable@vger.kernel.org>
Thank you, George
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 93802ab..3d47c34 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 -- 1.8.3.1
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