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

commit 4f15ee98304b96e164ff2340e1dfd6181c3f42aa upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 8f156a69912c8921193a11b0fe32fe257bedf8cd..04fafe95e9d1afedc8c46a13f1cfd390fd356368 100644 (file)
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1873,9 +1873,12 @@ 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);
 }