Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Zheyu Ma <zheyuma97@gmail.com>
To:     deller@gmx.de
Cc:     linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, Zheyu Ma <zheyuma97@gmail.com>
Subject: [PATCH 1/7] video: fbdev: i740fb: Error out if 'pixclock' equals zero
Date:   Mon,  4 Apr 2022 16:47:17 +0800
Message-Id: <20220404084723.79089-2-zheyuma97@gmail.com>
In-Reply-To: <20220404084723.79089-1-zheyuma97@gmail.com>
References: <20220404084723.79089-1-zheyuma97@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The userspace program could pass any values to the driver through
ioctl() interface. If the driver doesn't check the value of 'pixclock',
it may cause divide error.

Fix this by checking whether 'pixclock' is zero in the function
i740fb_check_var().

The following log reveals it:

divide error: 0000 [#1] PREEMPT SMP KASAN PTI
RIP: 0010:i740fb_decode_var drivers/video/fbdev/i740fb.c:444 [inline]
RIP: 0010:i740fb_set_par+0x272f/0x3bb0 drivers/video/fbdev/i740fb.c:739
Call Trace:
    fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1036
    do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1112
    fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1191
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:874 [inline]

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/i740fb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/i740fb.c b/drivers/video/fbdev/i740fb.c
index 52cce0db8bd3..b595437a5752 100644
--- a/drivers/video/fbdev/i740fb.c
+++ b/drivers/video/fbdev/i740fb.c
@@ -657,6 +657,9 @@ static int i740fb_decode_var(const struct fb_var_screeninfo *var,
 
 static int i740fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 {
+	if (!var->pixclock)
+		return -EINVAL;
+
 	switch (var->bits_per_pixel) {
 	case 8:
 		var->red.offset	= var->green.offset = var->blue.offset = 0;
-- 
2.25.1