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Wed, 27 May 2026 12:47:06 -0700 (PDT) Date: Wed, 27 May 2026 12:47:03 -0700 From: Dmitry Torokhov To: Jinmo Yang Cc: Jason Gerecke , Ping Cheng , Jiri Kosina , Benjamin Tissoires , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/1] HID: wacom: validate report size before kfifo insert Message-ID: References: <20260524135203.1996265-1-jinmo44.yang@gmail.com> <20260524135203.1996265-2-jinmo44.yang@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260524135203.1996265-2-jinmo44.yang@gmail.com> On Sun, May 24, 2026 at 10:52:03PM +0900, Jinmo Yang wrote: > wacom_wac_queue_insert() passes the report size directly to kfifo_in() > without checking whether the report fits in the kfifo buffer. > > Since commit 5e013ad20689 ("HID: wacom: Remove static WACOM_PKGLEN_MAX > limit"), the kfifo is sized dynamically as min(PAGE_SIZE, 10 * pktlen), > which can be as small as 256 bytes. However, reports received via > UHID_INPUT2 can be up to UHID_DATA_MAX (4096) bytes. When such an > oversized report reaches wacom_wac_queue_insert(), the existing > kfifo_avail() loop cannot make room for a record larger than the total > buffer, causing kfifo_copy_in() to memcpy up to 3840 bytes past the > slab allocation. Does it? Or maybe spins there indefinitely? Also, doesn't kfifo_copy_in() return 0 if a record it too big and not copy anything? > > Add a size check at the top of wacom_wac_queue_insert() to reject > reports that exceed the kfifo capacity. > > Fixes: 5e013ad20689 ("HID: wacom: Remove static WACOM_PKGLEN_MAX limit") > Cc: stable@vger.kernel.org > Signed-off-by: Jinmo Yang > --- > drivers/hid/wacom_sys.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c > index a32320b..cc82c6f 100644 > --- a/drivers/hid/wacom_sys.c > +++ b/drivers/hid/wacom_sys.c > @@ -54,6 +54,12 @@ static void wacom_wac_queue_insert(struct hid_device *hdev, > { > bool warned = false; > > + if (size > kfifo_size(fifo)) { > + hid_warn(hdev, "%s: report too large (%d > %u) for kfifo\n", > + __func__, size, kfifo_size(fifo)); > + return; > + } > + > while (kfifo_avail(fifo) < size) { > if (!warned) > hid_warn(hdev, "%s: kfifo has filled, starting to drop events\n", __func__); Thanks. -- Dmitry