HID: core: ensure the allocated report buffer can contain the reserved report ID

When the report ID is not used, the low level transport drivers expect
the first byte to be 0. However, currently the allocated buffer not
account for that extra byte, meaning that instead of having 8 guaranteed
bytes for implement to be working, we only have 7.

Reported-by: Alan Stern <[email protected]>
Closes: https://lore.kernel.org/linux-input/[email protected]/
Cc: [email protected]
Suggested-by: Alan Stern <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Benjamin Tissoires <[email protected]>

Author: Benjamin Tissoires

drivers/hid/hid-core.c

@@ -1883,9 +1883,12 @@ u8 *hid_alloc_report_buf(struct hid_report *report, gfp_t flags)
 	/*
 	 * 7 extra bytes are necessary to achieve proper functionality
 	 * of implement() working on 8 byte chunks
+	 * 1 extra byte for the report ID if it is null (not used) so
+	 * we can reserve that extra byte in the first position of the buffer
+	 * when sending it to .raw_request()
 	 */
 
-	u32 len = hid_report_len(report) + 7;
+	u32 len = hid_report_len(report) + 7 + (report->id == 0);
 
 	return kzalloc(len, flags);
 }