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Wed, 27 Oct 2021 20:32:30 +0000 From: George Kennedy To: gregkh@linuxfoundation.org, geert@linux-m68k.org, tzimmermann@suse.de, sam@ravnborg.org Cc: george.kennedy@oracle.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] video: fbdev: cirrusfb: check pixclock to avoid divide by zero Date: Wed, 27 Oct 2021 15:30:13 -0500 Message-Id: <1635366613-22507-1-git-send-email-george.kennedy@oracle.com> X-Mailer: git-send-email 1.8.3.1 Content-Type: text/plain X-ClientProxiedBy: BL0PR1501CA0036.namprd15.prod.outlook.com (2603:10b6:207:17::49) To BN0PR10MB5192.namprd10.prod.outlook.com (2603:10b6:408:115::8) MIME-Version: 1.0 Received: from dhcp-10-152-13-169.usdhcp.oraclecorp.com.com (209.17.40.36) by BL0PR1501CA0036.namprd15.prod.outlook.com (2603:10b6:207:17::49) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4628.18 via Frontend Transport; Wed, 27 Oct 2021 20:32:29 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: da15e9f1-70f7-49e8-2833-08d99988e5c8 X-MS-TrafficTypeDiagnostic: BN0PR10MB5224: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; 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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 --- 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