linux/drivers/usb/class
Tom Rix f4b9d8a582 USB: cdc-acm: rework notification_buffer resizing
Clang static analysis reports this error

cdc-acm.c:409:3: warning: Use of memory after it is freed
        acm_process_notification(acm, (unsigned char *)dr);

There are three problems, the first one is that dr is not reset

The variable dr is set with

if (acm->nb_index)
	dr = (struct usb_cdc_notification *)acm->notification_buffer;

But if the notification_buffer is too small it is resized with

		if (acm->nb_size) {
			kfree(acm->notification_buffer);
			acm->nb_size = 0;
		}
		alloc_size = roundup_pow_of_two(expected_size);
		/*
		 * kmalloc ensures a valid notification_buffer after a
		 * use of kfree in case the previous allocation was too
		 * small. Final freeing is done on disconnect.
		 */
		acm->notification_buffer =
			kmalloc(alloc_size, GFP_ATOMIC);

dr should point to the new acm->notification_buffer.

The second problem is any data in the notification_buffer is lost
when the pointer is freed.  In the normal case, the current data
is accumulated in the notification_buffer here.

	memcpy(&acm->notification_buffer[acm->nb_index],
	       urb->transfer_buffer, copy_size);

When a resize happens, anything before
notification_buffer[acm->nb_index] is garbage.

The third problem is the acm->nb_index is not reset on a
resizing buffer error.

So switch resizing to using krealloc and reassign dr and
reset nb_index.

Fixes: ea2583529c ("cdc-acm: reassemble fragmented notifications")
Signed-off-by: Tom Rix <trix@redhat.com>
Cc: stable <stable@vger.kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.com>
Link: https://lore.kernel.org/r/20200801152154.20683-1-trix@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-08-18 11:55:23 +02:00
..
cdc-acm.c USB: cdc-acm: rework notification_buffer resizing 2020-08-18 11:55:23 +02:00
cdc-acm.h cdc-acm: introduce a cool down 2020-04-16 14:59:49 +02:00
cdc-wdm.c usb: class: cdc-wdm: Provide description for usb_cdc_wdm_register()'s manage_power arg 2020-07-15 17:25:57 +02:00
Kconfig treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
Makefile USB: add SPDX identifiers to all remaining Makefiles 2017-11-07 15:53:48 +01:00
usblp.c usblp: poison URBs upon disconnect 2020-05-13 14:20:00 +02:00
usbtmc.c usb: Use fallthrough pseudo-keyword 2020-07-10 08:55:17 +02:00