From 711c68b3c0f7a924ffbee4aa962d8f62b85188ff Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Sun, 12 Feb 2012 06:00:41 +0000 Subject: [PATCH] cdc-wdm: Fix more races on the read path MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Tested-by: Bjørn Mork Cc: Oliver Neukum Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/usb/class/cdc-wdm.c | 16 +++++++++++----- 1 file 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: -- 2.20.1