linux.git/drivers/net/mctp/mctp-serial.c, branch master

mctp: serial: handle zero-length frames to prevent rx buffer overflow

2026-07-23T13:34:00Z

The MCTP serial receive state machine reads a frame length byte in mctp_serial_push_header() case 2 and validates it upper-bound-only: if (c > MCTP_SERIAL_FRAME_MTU) { dev->rxstate = STATE_ERR; } else { dev->rxlen = c; dev->rxpos = 0; dev->rxstate = STATE_DATA; ... } A length of zero passes this check, so rxlen is set to 0 and the state machine advances to STATE_DATA. In mctp_serial_push() STATE_DATA, the incoming byte is stored and rxpos incremented before the terminator is tested: dev->rxbuf[dev->rxpos] = c; dev->rxpos++; dev->rxstate = STATE_DATA; if (dev->rxpos == dev->rxlen) { dev->rxpos = 0; dev->rxstate = STATE_TRAILER; } With rxlen == 0 the "rxpos == rxlen" terminator can never fire (rxpos is already 1 on the first data byte), so subsequent bytes are written past the end of the fixed 74-byte rxbuf, which is the last member of the netdev private area. Every following data byte is an attacker-controlled 1-byte out-of-bounds heap write, and the overflow continues until a frame (0x7e) or escape byte resets the parser -- effectively unbounded. Reaching this requires CAP_NET_ADMIN to attach the N_MCTP line discipline and bring the resulting mctpserialN netdev up, after which the bytes arrive via the tty receive path. Route a zero-length frame straight to STATE_TRAILER instead of STATE_DATA. The trailer/framing bytes are still consumed, and the frame resolves to a zero-length skb that the MCTP core rejects; the parser never enters STATE_DATA with rxlen == 0, so the out-of-bounds write can no longer occur. KASAN, on a frame of 0x7e 0x01 0x00 followed by data bytes (before this change): UBSAN: array-index-out-of-bounds in drivers/net/mctp/mctp-serial.c:370 index 74 is out of range for type 'u8 [74]' BUG: KASAN: slab-out-of-bounds in mctp_serial_tty_receive_buf Write of size 1 at addr ... by task kworker/u16:0 mctp_serial_tty_receive_buf tty_ldisc_receive_buf flush_to_ldisc Allocated by task 152: alloc_netdev_mqs mctp_serial_open v2: route zero-length frames to STATE_TRAILER instead of STATE_ERR so the trailer/framing bytes are still consumed (Jeremy Kerr). Found by 0sec automated security-research tooling (https://0sec.ai). Fixes: a0c2ccd9b5ad ("mctp: Add MCTP-over-serial transport binding") Cc: stable@vger.kernel.org Suggested-by: Jeremy Kerr Assisted-by: 0sec:multi-model Signed-off-by: Doruk Tan Ozturk Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260715082021.46315-1-doruk@0sec.ai Signed-off-by: Paolo Abeni

net: mctp: Expose transport binding identifier via IFLA attribute

2024-11-09T17:04:54Z

MCTP control protocol implementations are transport binding dependent. Endpoint discovery is mandatory based on transport binding. Message timing requirements are specified in each respective transport binding specification. However, we currently have no means to get this information from MCTP links. Add a IFLA_MCTP_PHYS_BINDING netlink link attribute, which represents the transport type using the DMTF DSP0239-defined type numbers, returned as part of RTM_GETLINK data. We get an IFLA_MCTP_PHYS_BINDING attribute for each MCTP link, for example: - 0x00 (unspec) for loopback interface; - 0x01 (SMBus/I2C) for mctpi2c%d interfaces; and - 0x05 (serial) for mctpserial%d interfaces. Signed-off-by: Khang Nguyen Reviewed-by: Matt Johnston Link: https://patch.msgid.link/20241105071915.821871-1-khangng@os.amperecomputing.com Signed-off-by: Jakub Kicinski

Merge tag 'tty-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2024-09-26T16:59:50Z

Pull tty / serial driver updates from Greg KH: "Here is the "big" set of tty/serial driver updates for 6.12-rc1. Nothing major in here, just nice forward progress in the slow cleanup of the serial apis, and lots of other driver updates and fixes. Included in here are: - serial api updates from Jiri to make things more uniform and sane - 8250_platform driver cleanups - samsung serial driver fixes and updates - qcom-geni serial driver fixes from Johan for the bizarre UART engine that that chip seems to have. Hopefully it's in a better state now, but hardware designers still seem to come up with more ways to make broken UARTS 40+ years after this all should have finished. - sc16is7xx driver updates - omap 8250 driver updates - 8250_bcm2835aux driver updates - a few new serial driver bindings added - other serial minor driver updates All of these have been in linux-next for a long time with no reported problems" * tag 'tty-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (65 commits) tty: serial: samsung: Fix serial rx on Apple A7-A9 tty: serial: samsung: Fix A7-A11 serial earlycon SError tty: serial: samsung: Use bit manipulation macros for APPLE_S5L_* tty: rp2: Fix reset with non forgiving PCIe host bridges serial: 8250_aspeed_vuart: Enable module autoloading serial: qcom-geni: fix polled console corruption serial: qcom-geni: disable interrupts during console writes serial: qcom-geni: fix console corruption serial: qcom-geni: introduce qcom_geni_serial_poll_bitfield() serial: qcom-geni: fix arg types for qcom_geni_serial_poll_bit() soc: qcom: geni-se: add GP_LENGTH/IRQ_EN_SET/IRQ_EN_CLEAR registers serial: qcom-geni: fix false console tx restart serial: qcom-geni: fix fifo polling timeout tty: hvc: convert comma to semicolon mxser: convert comma to semicolon serial: 8250_bcm2835aux: Fix clock imbalance in PM resume serial: sc16is7xx: convert bitmask definitions to use BIT() macro serial: sc16is7xx: fix copy-paste errors in EFR_SWFLOWx_BIT constants serial: sc16is7xx: remove SC16IS7XX_MSR_DELTA_MASK serial: xilinx_uartps: Make cdns_rs485_supported static ...

net: mctp-serial: Fix missing escapes on transmit

2024-09-01T17:14:01Z

0x7d and 0x7e bytes are meant to be escaped in the data portion of frames, but this didn't occur since next_chunk_len() had an off-by-one error. That also resulted in the final byte of a payload being written as a separate tty write op. The chunk prior to an escaped byte would be one byte short, and the next call would never test the txpos+1 case, which is where the escaped byte was located. That meant it never hit the escaping case in mctp_serial_tx_work(). Example Input: 01 00 08 c8 7e 80 02 Previous incorrect chunks from next_chunk_len(): 01 00 08 c8 7e 80 02 With this fix: 01 00 08 c8 7e 80 02 Cc: stable@vger.kernel.org Fixes: a0c2ccd9b5ad ("mctp: Add MCTP-over-serial transport binding") Signed-off-by: Matt Johnston Signed-off-by: David S. Miller

net: mctp-serial: Add kunit test for next_chunk_len()

2024-09-01T17:14:01Z

Test various edge cases of inputs that contain characters that need escaping. This adds a new kunit suite for mctp-serial. Signed-off-by: Matt Johnston Signed-off-by: David S. Miller

mctp: serial: propagage new tty types

2024-08-14T06:25:21Z

In tty, u8 is now used for data, ssize_t for sizes (with possible negative error codes). Propagate these types (and use unsigned in next_chunk_len()) to mctp. Signed-off-by: Jiri Slaby (SUSE) Reviewed-by: Jeremy Kerr Cc: Greg Kroah-Hartman Cc: Jeremy Kerr Cc: Matt Johnston Cc: David S. Miller Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: netdev@vger.kernel.org Link: https://lore.kernel.org/r/20240808103549.429349-7-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: use u8 for flags

2023-08-11T19:12:45Z

This makes all those 'char's an explicit 'u8'. This is part of the continuing unification of chars and flags to be consistent u8. This approaches tty_port_default_receive_buf(). Note that we do not change signedness as we compile with -funsigned-char. Signed-off-by: "Jiri Slaby (SUSE)" Cc: William Hubbs Cc: Chris Brannon Cc: Kirk Reiser Cc: Samuel Thibault Cc: Marcel Holtmann Cc: Johan Hedberg Cc: Luiz Augusto von Dentz Cc: Dmitry Torokhov Cc: Arnd Bergmann Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Max Staudt Cc: Wolfgang Grandegger Cc: Marc Kleine-Budde Cc: Dario Binacchi Cc: Andreas Koensgen Cc: Jeremy Kerr Cc: Matt Johnston Cc: Krzysztof Kozlowski Cc: Liam Girdwood Cc: Mark Brown Cc: Jaroslav Kysela Cc: Takashi Iwai Acked-by: Mark Brown Link: https://lore.kernel.org/r/20230810091510.13006-18-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: use u8 for chars

2023-08-11T19:12:45Z

This makes all those 'unsigned char's an explicit 'u8'. This is part of the continuing unification of chars and flags to be consistent u8. This approaches tty_port_default_receive_buf(). Flags to be next. Signed-off-by: "Jiri Slaby (SUSE)" Cc: William Hubbs Cc: Chris Brannon Cc: Kirk Reiser Cc: Samuel Thibault Cc: Dmitry Torokhov Cc: Arnd Bergmann Cc: Max Staudt Cc: Wolfgang Grandegger Cc: Marc Kleine-Budde Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Dario Binacchi Cc: Andreas Koensgen Cc: Jeremy Kerr Cc: Matt Johnston Cc: Liam Girdwood Cc: Mark Brown Cc: Jaroslav Kysela Cc: Takashi Iwai Cc: Peter Ujfalusi Acked-by: Mark Brown Link: https://lore.kernel.org/r/20230810091510.13006-17-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: make tty_ldisc_ops::buf() hooks operate on size_t

2023-08-11T19:12:45Z

Count passed to tty_ldisc_ops::receive_buf*(), ::lookahead_buf(), and returned from ::receive_buf2() is expected to be size_t. So set it to size_t to unify with the rest of the code. Signed-off-by: "Jiri Slaby (SUSE)" Cc: William Hubbs Cc: Chris Brannon Cc: Kirk Reiser Cc: Samuel Thibault Cc: Marcel Holtmann Cc: Johan Hedberg Cc: Luiz Augusto von Dentz Cc: Dmitry Torokhov Cc: Arnd Bergmann Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Max Staudt Cc: Wolfgang Grandegger Cc: Marc Kleine-Budde Cc: Dario Binacchi Cc: Andreas Koensgen Cc: Jeremy Kerr Cc: Matt Johnston Cc: Krzysztof Kozlowski Cc: Liam Girdwood Cc: Mark Brown Cc: Jaroslav Kysela Cc: Takashi Iwai Acked-by: Mark Brown Link: https://lore.kernel.org/r/20230810091510.13006-16-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

mctp: serial: Fix starting value for frame check sequence

2022-12-19T12:38:45Z

RFC1662 defines the start state for the crc16 FCS to be 0xffff, but we're currently starting at zero. This change uses the correct start state. We're only early in the adoption for the serial binding, so there aren't yet any other users to interface to. Fixes: a0c2ccd9b5ad ("mctp: Add MCTP-over-serial transport binding") Reported-by: Harsh Tyagi Tested-by: Harsh Tyagi Signed-off-by: Jeremy Kerr Reviewed-by: Alexander Duyck Signed-off-by: David S. Miller

linux.git/drivers/net/mctp/mctp-serial.c, branch master

mctp: serial: handle zero-length frames to prevent rx buffer overflow

net: mctp: Expose transport binding identifier via IFLA attribute

Merge tag 'tty-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

net: mctp-serial: Fix missing escapes on transmit

net: mctp-serial: Add kunit test for next_chunk_len()

mctp: serial: propagage new tty types

tty: use u8 for flags

tty: use u8 for chars

tty: make tty_ldisc_ops::*buf*() hooks operate on size_t

mctp: serial: Fix starting value for frame check sequence

tty: make tty_ldisc_ops::buf() hooks operate on size_t