Commit 4f15ee98 authored Jul 10, 2025 by Benjamin Tissoires

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 <stern@rowland.harvard.edu>
Closes: https://lore.kernel.org/linux-input/c75433e0-9b47-4072-bbe8-b1d14ea97b13@rowland.harvard.edu/

Cc: stable@vger.kernel.org
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://patch.msgid.link/20250710-report-size-null-v2-1-ccf922b7c4e5@kernel.org

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

parent 04515e08

drivers/hid/hid-core.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}