USB: fix DoS in pwc USB video driver

the pwc driver has a disconnect method that waits for user space to
close the device. This opens up an opportunity for a DoS attack,
blocking the USB subsystem and making khubd's task busy wait in
kernel space. This patch shifts freeing resources to close if an opened
device is disconnected.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
CC: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 36 insertions, 17 deletions

diff --git a/drivers/media/video/pwc/pwc-if.c b/drivers/media/video/pwc/pwc-if.c
index 9c0e8d18c2f6..3d81966d8c42 100644
--- a/drivers/media/video/pwc/pwc-if.c
+++ b/drivers/media/video/pwc/pwc-if.c
@@ -1196,12 +1196,19 @@ static int pwc_video_open(struct inode *inode, struct file *file)
         return 0;
 }
 
+
+static void pwc_cleanup(struct pwc_device *pdev)
+{
+        pwc_remove_sysfs_files(pdev->vdev);
+        video_unregister_device(pdev->vdev);
+}
+
 /* Note that all cleanup is done in the reverse order as in _open */
 static int pwc_video_close(struct inode *inode, struct file *file)
 {
         struct video_device *vdev = file->private_data;
         struct pwc_device *pdev;
-        int i;
+        int i, hint;
 
         PWC_DEBUG_OPEN(">> video_close called(vdev = 0x%p).\n", vdev);
 
@@ -1224,8 +1231,9 @@ static int pwc_video_close(struct inode *inode, struct file *file)
         pwc_isoc_cleanup(pdev);
         pwc_free_buffers(pdev);
 
+        lock_kernel();
         /* Turn off LEDS and power down camera, but only when not unplugged */
-        if (pdev->error_status != EPIPE) {
+        if (!pdev->unplugged) {
                 /* Turn LEDs off */
                 if (pwc_set_leds(pdev, 0, 0) < 0)
                         PWC_DEBUG_MODULE("Failed to set LED on/off time.\n");
@@ -1234,9 +1242,19 @@ static int pwc_video_close(struct inode *inode, struct file *file)
                         if (i < 0)
                                 PWC_ERROR("Failed to power down camera (%d)\n", i);
                 }
+                pdev->vopen--;
+                PWC_DEBUG_OPEN("<< video_close() vopen=%d\n", i);
+        } else {
+                pwc_cleanup(pdev);
+                /* Free memory (don't set pdev to 0 just yet) */
+                kfree(pdev);
+                /* search device_hint[] table if we occupy a slot, by any chance */
+                for (hint = 0; hint < MAX_DEV_HINTS; hint++)
+                        if (device_hint[hint].pdev == pdev)
+                                device_hint[hint].pdev = NULL;
         }
-        pdev->vopen--;
-        PWC_DEBUG_OPEN("<< video_close() vopen=%d\n", pdev->vopen);
+        unlock_kernel();
+
         return 0;
 }
 
@@ -1791,21 +1809,21 @@ static void usb_pwc_disconnect(struct usb_interface *intf)
         /* Alert waiting processes */
         wake_up_interruptible(&pdev->frameq);
         /* Wait until device is closed */
-        while (pdev->vopen)
-                schedule();
-        /* Device is now closed, so we can safely unregister it */
-        PWC_DEBUG_PROBE("Unregistering video device in disconnect().\n");
-        pwc_remove_sysfs_files(pdev->vdev);
-        video_unregister_device(pdev->vdev);
-
-        /* Free memory (don't set pdev to 0 just yet) */
-        kfree(pdev);
+        if(pdev->vopen) {
+                pdev->unplugged = 1;
+        } else {
+                /* Device is closed, so we can safely unregister it */
+                PWC_DEBUG_PROBE("Unregistering video device in disconnect().\n");
+                pwc_cleanup(pdev);
+                /* Free memory (don't set pdev to 0 just yet) */
+                kfree(pdev);
 
 disconnect_out:
-        /* search device_hint[] table if we occupy a slot, by any chance */
-        for (hint = 0; hint < MAX_DEV_HINTS; hint++)
-                if (device_hint[hint].pdev == pdev)
-                        device_hint[hint].pdev = NULL;
+                /* search device_hint[] table if we occupy a slot, by any chance */
+                for (hint = 0; hint < MAX_DEV_HINTS; hint++)
+                        if (device_hint[hint].pdev == pdev)
+                                device_hint[hint].pdev = NULL;
+        }
 
         unlock_kernel();
 }
diff --git a/drivers/media/video/pwc/pwc.h b/drivers/media/video/pwc/pwc.h
index 910a04f53920..8e8e5b27e77e 100644
--- a/drivers/media/video/pwc/pwc.h
+++ b/drivers/media/video/pwc/pwc.h
@@ -193,6 +193,7 @@ struct pwc_device
    char vsnapshot;              /* snapshot mode */
    char vsync;                  /* used by isoc handler */
    char vmirror;                /* for ToUCaM series */
+        char unplugged;
 
    int cmd_len;
    unsigned char cmd_buf[13];