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Tue, 18 Aug 2026 22:42:05 -0700 (PDT) Received: from Mac.lan ([125.128.148.126]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-851d3389fcfsm214485b3a.18.2026.08.18.22.42.03 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 18 Aug 2026 22:42:05 -0700 (PDT) From: Baul Lee To: max@enpas.org, mkl@pengutronix.de, mailhol@kernel.org Cc: linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, federico.kirschbaum@xbow.com Subject: [PATCH net] can: can327: Fix stack out-of-bounds write in can327_handle_prompt() Date: Wed, 19 Aug 2026 14:42:01 +0900 Message-ID: <20260819054201.67294-1-baul.lee@xbow.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit can327_handle_prompt() hexdumps the frame queued for transmission, two hex characters per payload byte, into an 18-byte on-stack buffer sized for a classical 8-byte payload. The loop runs frame->len times without a clamp, and frame is a struct can_frame copied verbatim from the skb passed to can327_netdev_start_xmit(). A CAN XL frame aliases struct can_frame such that canxl_frame.flags, which must carry CANXL_XLF, overlaps can_frame.len, so it arrives with frame->len == 0x80. can327 is a classical CAN device, but can_dev_dropped_skb() only rejects CAN FD for a non-FD device; for ETH_P_CANXL, can_dropped_invalid_skb() checks only that the frame is a well-formed CAN XL frame, not that the device supports one. The smallest such frame, CANXL_HDR_SIZE + CANXL_MIN_DLEN, is 13 bytes, so it also passes the MTU check on a CAN_MTU device. CAN_RAW rejects it, as raw_check_txframe() requires CAN_CAP_XL, but an AF_PACKET SOCK_RAW socket does not go through that check. The loop then writes 128 hex pairs over the buffer and past the end of the stack frame: BUG: KASAN: stack-out-of-bounds in vsnprintf+0x550/0x83c Write of size 1 at addr ffff800085407a32 by task kworker/u18:0/36 Call trace: vsnprintf+0x550/0x83c snprintf+0xa4/0xe0 can327_handle_prompt+0x5c4/0x69c can327_parse_rxbuf+0x618/0xb50 can327_ldisc_rx+0x118/0x1c0 tty_ldisc_receive_buf+0xc0/0xe0 flush_to_ldisc+0x11c/0x278 This frame has 1 object: [32, 50) 'local_txbuf' Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: can327_handle_prompt+0x66c/0x69c Clamp the dump to CAN_MAX_DLEN, which is what the buffer is sized for. Discovered by XBOW, triaged by Baul Lee Fixes: fb08cba12b52 ("can: canxl: update CAN infrastructure for CAN XL frames") Signed-off-by: Baul Lee --- drivers/net/can/can327.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/can/can327.c b/drivers/net/can/can327.c index 90f5e35f3c8f..396db56775a6 100644 --- a/drivers/net/can/can327.c +++ b/drivers/net/can/can327.c @@ -624,9 +624,10 @@ static void can327_handle_prompt(struct can327 *elm) snprintf(local_txbuf, sizeof(local_txbuf), "ATRTR\r"); } else { /* Send a regular CAN data frame */ + int dlc = min_t(int, frame->len, CAN_MAX_DLEN); int i; - for (i = 0; i < frame->len; i++) { + for (i = 0; i < dlc; i++) { snprintf(&local_txbuf[2 * i], sizeof(local_txbuf), "%02X", frame->data[i]); -- 2.50.1