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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: ea2583529cd1 ("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>
f4b9d8a582