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Thu, 28 May 2026 10:59:49 -0700 (PDT) Received: from jmoon ([118.220.156.4]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-841d6eac68esm5749843b3a.15.2026.05.28.10.59.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 10:59:48 -0700 (PDT) From: Jinmo Yang To: linux-input@vger.kernel.org, dmitry.torokhov@gmail.com Cc: jikos@kernel.org, benjamin.tissoires@redhat.com, stable@vger.kernel.org, Jinmo Yang Subject: [PATCH v2] HID: wacom: fix slab-out-of-bounds write in wacom_wac_queue_insert Date: Fri, 29 May 2026 02:59:45 +0900 Message-ID: <20260528175945.2987781-1-jinmo44.yang@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260524135203.1996265-1-jinmo44.yang@gmail.com> References: <20260524135203.1996265-1-jinmo44.yang@gmail.com> Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit wacom_wac_queue_insert() calls kfifo_skip() in a loop when the kfifo doesn't have enough space for the incoming report. If the kfifo is empty, kfifo_skip() reads stale data left in the kmalloc'd buffer via __kfifo_peek_n() and interprets it as a record length, advancing fifo->out by that garbage value. This corrupts the internal kfifo state, causing kfifo_unused() to return a value much larger than the actual buffer size, which bypasses __kfifo_in_r()'s guard: if (len + recsize > kfifo_unused(fifo)) return 0; kfifo_copy_in() then performs an out-of-bounds memcpy, writing up to 3842 bytes past the 256-byte buffer. Add a !kfifo_is_empty() condition to the while loop so kfifo_skip() is never called on an empty fifo, and check the return value of kfifo_in() to reject reports that are too large for the fifo. Suggested-by: Dmitry Torokhov Fixes: 5e013ad20689 ("HID: wacom: Remove static WACOM_PKGLEN_MAX limit") Cc: stable@vger.kernel.org Signed-off-by: Jinmo Yang --- Changes in v2: - Instead of a size check at the top, add !kfifo_is_empty() to the while loop condition to prevent kfifo_skip() on an empty fifo (Suggested by Dmitry Torokhov) - Check kfifo_in() return value to reject oversized reports instead of a separate guard drivers/hid/wacom_sys.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c index a32320b35..489ca68f1 100644 --- a/drivers/hid/wacom_sys.c +++ b/drivers/hid/wacom_sys.c @@ -54,7 +54,7 @@ static void wacom_wac_queue_insert(struct hid_device *hdev, { bool warned = false; - while (kfifo_avail(fifo) < size) { + while (kfifo_avail(fifo) < size && !kfifo_is_empty(fifo)) { if (!warned) hid_warn(hdev, "%s: kfifo has filled, starting to drop events\n", __func__); warned = true; @@ -62,7 +62,9 @@ static void wacom_wac_queue_insert(struct hid_device *hdev, kfifo_skip(fifo); } - kfifo_in(fifo, raw_data, size); + if (!kfifo_in(fifo, raw_data, size)) + hid_warn_ratelimited(hdev, "%s: report is too large (%d)\n", + __func__, size); } static void wacom_wac_queue_flush(struct hid_device *hdev, -- 2.53.0