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cdc-wdm: Fix more races on the read path

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We must not allow the input buffer length to change while we're
shuffling the buffer contents.  We also mustn't clear the WDM_READ
flag after more data might have arrived.  Therefore move both of these
into the spinlocked region at the bottom of wdm_read().

When reading desc->length without holding the iuspin lock, use
ACCESS_ONCE() to ensure the compiler doesn't re-read it with
inconsistent results.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Tested-by: Bjørn Mork <bjorn@mork.no>
Cc: Oliver Neukum <oliver@neukum.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ben Hutchings 2012-02-12 06:00:41 +00:00 committed by Greg Kroah-Hartman
parent c192c8e71a
commit 711c68b3c0
1 changed files with 11 additions and 5 deletions
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16
drivers/usb/class/cdc-wdm.c
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@ -391,7 +391,7 @@ outnl:
static ssize_t wdm_read
(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
int rv, cntr = 0;
int rv, cntr;
int i = 0;
struct wdm_device *desc = file->private_data;
@ -400,7 +400,8 @@ static ssize_t wdm_read
if (rv < 0)
return -ERESTARTSYS;
if (desc->length == 0) {
cntr = ACCESS_ONCE(desc->length);
if (cntr == 0) {
desc->read = 0;
retry:
if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
@ -455,25 +456,30 @@ retry:
goto retry;
}
clear_bit(WDM_READ, &desc->flags);
cntr = desc->length;
spin_unlock_irq(&desc->iuspin);
}
cntr = count > desc->length ? desc->length : count;
if (cntr > count)
cntr = count;
rv = copy_to_user(buffer, desc->ubuf, cntr);
if (rv > 0) {
rv = -EFAULT;
goto err;
}
spin_lock_irq(&desc->iuspin);
for (i = 0; i < desc->length - cntr; i++)
desc->ubuf[i] = desc->ubuf[i + cntr];
spin_lock_irq(&desc->iuspin);
desc->length -= cntr;
spin_unlock_irq(&desc->iuspin);
/* in case we had outstanding data */
if (!desc->length)
clear_bit(WDM_READ, &desc->flags);
spin_unlock_irq(&desc->iuspin);
rv = cntr;
err: