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USB: ldusb: fix ring-buffer locking 

The custom ring-buffer implementation was merged without any locking or
explicit memory barriers, but a spinlock was later added by commit
9d33efd9a7 ("USB: ldusb bugfix").

The lock did not cover the update of the tail index once the entry had
been processed, something which could lead to memory corruption on
weakly ordered architectures or due to compiler optimisations.

Specifically, a completion handler running on another CPU might observe
the incremented tail index and update the entry before ld_usb_read() is
done with it.

Fixes: 2824bd250f ("[PATCH] USB: add ldusb driver")
Fixes: 9d33efd9a7 ("USB: ldusb bugfix")
Cc: stable <stable@vger.kernel.org>     # 2.6.13
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191022143203.5260-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold 2019-10-22 16:32:02 +02:00 committed by Greg Kroah-Hartman
parent d482c7bb05
commit d98ee2a19c
1 changed files with 2 additions and 2 deletions
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4
drivers/usb/misc/ldusb.c
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@ -495,11 +495,11 @@ static ssize_t ld_usb_read(struct file *file, char __user *buffer, size_t count,
retval = -EFAULT;
goto unlock_exit;
}
dev->ring_tail = (dev->ring_tail+1) % ring_buffer_size;
retval = bytes_to_read;
spin_lock_irq(&dev->rbsl);
dev->ring_tail = (dev->ring_tail + 1) % ring_buffer_size;
if (dev->buffer_overflow) {
dev->buffer_overflow = 0;
spin_unlock_irq(&dev->rbsl);