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| author | Ben Hutchings <ben@decadent.org.uk> | 2012-02-12 06:00:41 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-02-24 13:11:56 -0800 |
| commit | 711c68b3c0f7a924ffbee4aa962d8f62b85188ff (patch) | |
| tree | 364aa61ad7714ae92264ae06e304fc4fd8171dd0 /drivers/usb/class | |
| parent | c192c8e71a2ded01170c1a992cd21aaedc822756 (diff) | |
| download | linux-711c68b3c0f7a924ffbee4aa962d8f62b85188ff.tar.gz | |
cdc-wdm: Fix more races on the read path
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>
Diffstat (limited to 'drivers/usb/class')
| -rw-r--r-- | drivers/usb/class/cdc-wdm.c | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c index b27bbb957e16..7ca54d4dea92 100644 --- a/drivers/usb/class/cdc-wdm.c +++ b/drivers/usb/class/cdc-wdm.c @@ -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: |