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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:
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||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.