[ 29/75] USB: cdc-wdm: fix race leading leading to memory corruption

[Greg KH]

3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oliver Neukum <oliver@xxxxxxxxxx>

commit 5c22837adca7c30b66121cf18ad3e160134268d4 upstream.

This patch fixes a race whereby a pointer to a buffer
would be overwritten while the buffer was in use leading
to a double free and a memory leak. This causes crashes.
This bug was introduced in 2.6.34

Signed-off-by: Oliver Neukum <oneukum@xxxxxxx>
Tested-by: Bjørn Mork <bjorn@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/class/cdc-wdm.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -108,8 +108,9 @@ static void wdm_out_callback(struct urb
 	spin_lock(&desc->iuspin);
 	desc->werr = urb->status;
 	spin_unlock(&desc->iuspin);
-	clear_bit(WDM_IN_USE, &desc->flags);
 	kfree(desc->outbuf);
+	desc->outbuf = NULL;
+	clear_bit(WDM_IN_USE, &desc->flags);
 	wake_up(&desc->wait);
 }
 
@@ -312,7 +313,7 @@ static ssize_t wdm_write
 	if (we < 0)
 		return -EIO;
 
-	desc->outbuf = buf = kmalloc(count, GFP_KERNEL);
+	buf = kmalloc(count, GFP_KERNEL);
 	if (!buf) {
 		rv = -ENOMEM;
 		goto outnl;
@@ -376,10 +377,12 @@ static ssize_t wdm_write
 	req->wIndex = desc->inum;
 	req->wLength = cpu_to_le16(count);
 	set_bit(WDM_IN_USE, &desc->flags);
+	desc->outbuf = buf;
 
 	rv = usb_submit_urb(desc->command, GFP_KERNEL);
 	if (rv < 0) {
 		kfree(buf);
+		desc->outbuf = NULL;
 		clear_bit(WDM_IN_USE, &desc->flags);
 		dev_err(&desc->intf->dev, "Tx URB error: %d\n", rv);
 	} else {


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