[PATCH 5.19 099/717] fbdev: smscufx: Fix use-after-free in ufx_ops_open()

Greg Kroah-Hartman
2022-10-22T07:56:04Z

From: Hyunwoo Kim <imv4bel@gmail.com>

commit 5610bcfe8693c02e2e4c8b31427f1bdbdecc839c upstream.

A race condition may occur if the user physically removes the
USB device while calling open() for this device node.

This is a race condition between the ufx_ops_open() function and
the ufx_usb_disconnect() function, which may eventually result in UAF.

So, add a mutex to the ufx_ops_open() and ufx_usb_disconnect() functions
to avoid race contidion of krefs.

Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/video/fbdev/smscufx.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

--- a/drivers/video/fbdev/smscufx.c
+++ b/drivers/video/fbdev/smscufx.c
@@ -137,6 +137,8 @@ static int ufx_submit_urb(struct ufx_dat
static int ufx_alloc_urb_list(struct ufx_data *dev, int count, size_t size);
static void ufx_free_urb_list(struct ufx_data *dev);

+static DEFINE_MUTEX(disconnect_mutex);
+
/* reads a control register */
static int ufx_reg_read(struct ufx_data *dev, u32 index, u32 *data)
{
@@ -1071,9 +1073,13 @@ static int ufx_ops_open(struct fb_info *
if (user == 0 && !console)
return -EBUSY;

+ mutex_lock(&disconnect_mutex);
+
/* If the USB device is gone, we don't accept new opens */
- if (dev->virtualized)
+ if (dev->virtualized) {
+ mutex_unlock(&disconnect_mutex);
return -ENODEV;
+ }

dev->fb_count++;

@@ -1097,6 +1103,8 @@ static int ufx_ops_open(struct fb_info *
pr_debug("open /dev/fb%d user=%d fb_info=%p count=%d",
info->node, user, info, dev->fb_count);

+ mutex_unlock(&disconnect_mutex);
+
return 0;
}

@@ -1741,6 +1749,8 @@ static void ufx_usb_disconnect(struct us
{
struct ufx_data *dev;

+ mutex_lock(&disconnect_mutex);
+
dev = usb_get_intfdata(interface);

pr_debug("USB disconnect starting\n");
@@ -1761,6 +1771,8 @@ static void ufx_usb_disconnect(struct us
kref_put(&dev->kref, ufx_free);

/* consider ufx_data freed */
+
+ mutex_unlock(&disconnect_mutex);
}

static struct usb_driver ufx_driver = {