HID: wacom: fix memory leak on size mismatch in wacom_wac_queue_flush()

JIRA: https://issues.redhat.com/browse/RHEL-102058
Upstream Status: since v6.15

commit fd34bf7
Author: Qasim Ijaz <qasdev00@gmail.com>
Date:   Mon Apr 14 19:33:09 2025 +0100

    HID: wacom: fix memory leak on size mismatch in wacom_wac_queue_flush()

    In wacom_wac_queue_flush() the code allocates zero initialised
    buffer which it uses as a storage buffer for copying data from
    a fifo via kfifo_out(). The kfifo_out() function returns the
    number of elements it has copied. The code checks if the number
    of copied elements does not equal the size of the fifo record,
    if it does not it simply skips the entry and continues to the
    next iteration. However it does not release the storage buffer
    leading to a memory leak.

    Fix the memory leak by freeing the buffer on size mismatch.

    Fixes: 5e013ad ("HID: wacom: Remove static WACOM_PKGLEN_MAX limit")
    Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
    Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
    Signed-off-by: Jiri Kosina <jkosina@suse.com>

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

Author: bentiss

drivers/hid/wacom_sys.c

@@ -87,6 +87,7 @@ static void wacom_wac_queue_flush(struct hid_device *hdev,
 			// to flush seems reasonable enough, however.
 			hid_warn(hdev, "%s: removed fifo entry with unexpected size\n",
 				 __func__);
+			kfree(buf);
 			continue;
 		}
 		err = hid_report_raw_event(hdev, HID_INPUT_REPORT, buf, size, false);