[ 24/47] USB: cdc-wdm: fix race leading leading to memory corruption

Greg KH
2012-05-04T20:56:06Z

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

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From: Oliver Neukum <oliver@neukum.org>

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@suse.de>
Tested-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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 {