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From:   Wang Hai <wanghai38@huawei.com>
To:     <steve.glendinning@shawell.net>, <FlorianSchandinat@gmx.de>,
        <gregkh@suse.de>
CC:     <linux-fbdev@vger.kernel.org>, <dri-devel@lists.freedesktop.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH] video: smscufx: Fix null-ptr-deref in ufx_usb_probe()
Date:   Thu, 14 Oct 2021 21:22:31 +0800
Message-ID: <20211014132231.555138-1-wanghai38@huawei.com>
MIME-Version: 1.0
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Precedence: bulk

I got a null-ptr-deref report:

BUG: kernel NULL pointer dereference, address: 0000000000000000
...
RIP: 0010:fb_destroy_modelist+0x38/0x100
...
Call Trace:
 ufx_usb_probe.cold+0x2b5/0xac1 [smscufx]
 usb_probe_interface+0x1aa/0x3c0 [usbcore]
 really_probe+0x167/0x460
...
 ret_from_fork+0x1f/0x30

If fb_alloc_cmap() fails in ufx_usb_probe(), fb_destroy_modelist() will
be called to destroy modelist in the error handling path. But modelist
has not been initialized yet, so it will result in null-ptr-deref.

Initialize modelist before calling fb_alloc_cmap() to fix this bug.

Fixes: 3c8a63e22a08 ("Add support for SMSC UFX6000/7000 USB display adapters")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
---
 drivers/video/fbdev/smscufx.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/video/fbdev/smscufx.c b/drivers/video/fbdev/smscufx.c
index bfac3ee4a642..28768c272b73 100644
--- a/drivers/video/fbdev/smscufx.c
+++ b/drivers/video/fbdev/smscufx.c
@@ -1656,6 +1656,7 @@ static int ufx_usb_probe(struct usb_interface *interface,
 	info->par = dev;
 	info->pseudo_palette = dev->pseudo_palette;
 	info->fbops = &ufx_ops;
+	INIT_LIST_HEAD(&info->modelist);
 
 	retval = fb_alloc_cmap(&info->cmap, 256, 0);
 	if (retval < 0) {
@@ -1666,8 +1667,6 @@ static int ufx_usb_probe(struct usb_interface *interface,
 	INIT_DELAYED_WORK(&dev->free_framebuffer_work,
 			  ufx_free_framebuffer_work);
 
-	INIT_LIST_HEAD(&info->modelist);
-
 	retval = ufx_reg_read(dev, 0x3000, &id_rev);
 	check_warn_goto_error(retval, "error %d reading 0x3000 register from device", retval);
 	dev_dbg(dev->gdev, "ID_REV register value 0x%08x", id_rev);
-- 
2.25.1