kernel/linux.git/drivers/net/caif/caif_serial.c, branch linux-7.0.y

serial: caif: hold tty->link reference in ldisc_open and ser_release

2026-03-10T01:47:55+00:00

A reproducer triggers a KASAN slab-use-after-free in pty_write_room() when caif_serial's TX path calls tty_write_room(). The faulting access is on tty->link->port. Hold an extra kref on tty->link for the lifetime of the caif_serial line discipline: get it in ldisc_open() and drop it in ser_release(), and also drop it on the ldisc_open() error path. With this change applied, the reproducer no longer triggers the UAF in my testing. Link: https://gist.github.com/shuangpengbai/c898debad6bdf170a84be7e6b3d8707f Link: https://lore.kernel.org/netdev/20260301220525.1546355-1-shuangpeng.kernel@gmail.com Fixes: e31d5a05948e ("caif: tty's are kref objects so take a reference") Signed-off-by: Shuangpeng Bai Reviewed-by: Jiayuan Chen Link: https://patch.msgid.link/20260306034006.3395740-1-shuangpeng.kernel@gmail.com Signed-off-by: Jakub Kicinski

serial: caif: fix use-after-free in caif_serial ldisc_close()

2026-02-10T14:23:11+00:00

There is a use-after-free bug in caif_serial where handle_tx() may access ser->tty after the tty has been freed. The race condition occurs between ldisc_close() and packet transmission: CPU 0 (close) CPU 1 (xmit) ------------- ------------ ldisc_close() tty_kref_put(ser->tty) [tty may be freed here] <-- race window --> caif_xmit() handle_tx() tty = ser->tty // dangling ptr tty->ops->write() // UAF! schedule_work() ser_release() unregister_netdevice() The root cause is that tty_kref_put() is called in ldisc_close() while the network device is still active and can receive packets. Since ser and tty have a 1:1 binding relationship with consistent lifecycles (ser is allocated in ldisc_open and freed in ser_release via unregister_netdevice, and each ser binds exactly one tty), we can safely defer the tty reference release to ser_release() where the network device is unregistered. Fix this by moving tty_kref_put() from ldisc_close() to ser_release(), after unregister_netdevice(). This ensures the tty reference is held as long as the network device exists, preventing the UAF. Note: We save ser->tty before unregister_netdevice() because ser is embedded in netdev's private data and will be freed along with netdev (needs_free_netdev = true). How to reproduce: Add mdelay(500) at the beginning of ldisc_close() to widen the race window, then run the reproducer program [1]. Note: There is a separate deadloop issue in handle_tx() when using PORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper serial backend). This deadloop exists even without this patch, and is likely caused by inconsistency between uart_write_room() and uart_write() in serial core. It has been addressed in a separate patch [2]. KASAN report: ================================================================== BUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620 Read of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929 Call Trace: dump_stack_lvl+0x10e/0x1f0 print_report+0xd0/0x630 kasan_report+0xe4/0x120 handle_tx+0x5d1/0x620 dev_hard_start_xmit+0x9d/0x6c0 __dev_queue_xmit+0x6e2/0x4410 packet_xmit+0x243/0x360 packet_sendmsg+0x26cf/0x5500 __sys_sendto+0x4a3/0x520 __x64_sys_sendto+0xe0/0x1c0 do_syscall_64+0xc9/0xf80 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f615df2c0d7 Allocated by task 9930: Freed by task 64: Last potentially related work creation: The buggy address belongs to the object at ffff8881131e1000 which belongs to the cache kmalloc-cg-2k of size 2048 The buggy address is located 1168 bytes inside of freed 2048-byte region [ffff8881131e1000, ffff8881131e1800) The buggy address belongs to the physical page: page_owner tracks the page as allocated page last free pid 9778 tgid 9778 stack trace: Memory state around the buggy address: ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== [1]: https://gist.github.com/mrpre/f683f244544f7b11e7fa87df9e6c2eeb [2]: https://lore.kernel.org/linux-serial/20260204074327.226165-1-jiayuan.chen@linux.dev/T/#u Reported-by: syzbot+827272712bd6d12c79a4@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000a4a7550611e234f5@google.com/T/ Fixes: 56e0ef527b18 ("drivers/net: caif: fix wrong rtnl_is_locked() usage") Reviewed-by: Greg Kroah-Hartman Signed-off-by: Jiayuan Chen Reviewed-by: Jijie Shao Link: https://patch.msgid.link/20260206074450.154267-1-jiayuan.chen@linux.dev Signed-off-by: Paolo Abeni

tty: caif: removed unused function debugfs_tx()

2025-03-20T15:08:50+00:00

Remove debugfs_tx() which was added when the caif driver was added in commit 9b27105b4a44 ("net-caif-driver: add CAIF serial driver (ldisc)") but it has never been used. Flagged by LLVM 19.1.7 W=1 builds. Signed-off-by: Simon Horman Link: https://lore.kernel.org/r/20250320-caif-debugfs-tx-v1-1-be5654770088@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: caif: do not use N_TTY_BUF_SIZE

2025-03-20T15:00:50+00:00

N_TTY_BUF_SIZE -- as the name suggests -- is the N_TTY's buffer size. There is no reason to couple that to caif's tty->receive_room. Use 4096 directly -- even though, it should be some sort of "SKB_MAX_ALLOC" or alike. But definitely not N_TTY_BUF_SIZE. N_TTY_BUF_SIZE is private and will be moved to n_tty.c later. Signed-off-by: Jiri Slaby (SUSE) Acked-by: Jakub Kicinski Cc: Andrew Lunn Cc: David S. Miller Cc: Eric Dumazet Cc: Paolo Abeni Cc: netdev@vger.kernel.org Link: https://lore.kernel.org/r/20250317070046.24386-4-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: use u8 for flags

2023-08-11T19:12:45+00:00

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

2023-08-11T19:12:45+00:00

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

net: caif: Use netif_rx().

2022-03-04T12:02:19+00:00

Since commit baebdf48c3600 ("net: dev: Makes sure netif_rx() can be invoked in any context.") the function netif_rx() can be used in preemptible/thread context as well as in interrupt context. Use netif_rx(). Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: David S. Miller

Merge tag 'tty-5.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2021-07-05T21:08:24+00:00

Pull tty / serial updates from Greg KH: "Here is the big set of tty and serial driver patches for 5.14-rc1. A bit more than normal, but nothing major, lots of cleanups. Highlights are: - lots of tty api cleanups and mxser driver cleanups from Jiri - build warning fixes - various serial driver updates - coding style cleanups - various tty driver minor fixes and updates - removal of broken and disable r3964 line discipline (finally!) All of these have been in linux-next for a while with no reported issues" * tag 'tty-5.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (227 commits) serial: mvebu-uart: remove unused member nb from struct mvebu_uart arm64: dts: marvell: armada-37xx: Fix reg for standard variant of UART dt-bindings: mvebu-uart: fix documentation serial: mvebu-uart: correctly calculate minimal possible baudrate serial: mvebu-uart: do not allow changing baudrate when uartclk is not available serial: mvebu-uart: fix calculation of clock divisor tty: make linux/tty_flip.h self-contained serial: Prefer unsigned int to bare use of unsigned serial: 8250: 8250_omap: Fix possible interrupt storm on K3 SoCs serial: qcom_geni_serial: use DT aliases according to DT bindings Revert "tty: serial: Add UART driver for Cortina-Access platform" tty: serial: Add UART driver for Cortina-Access platform MAINTAINERS: add me back as mxser maintainer mxser: Documentation, fix typos mxser: Documentation, make the docs up-to-date mxser: Documentation, remove traces of callout device mxser: introduce mxser_16550A_or_MUST helper mxser: rename flags to old_speed in mxser_set_serial_info mxser: use port variable in mxser_set_serial_info mxser: access info->MCR under info->slock ...

net: caif: fix memory leak in ldisc_open

2021-06-14T19:28:16+00:00

Syzbot reported memory leak in tty_init_dev(). The problem was in unputted tty in ldisc_open() static int ldisc_open(struct tty_struct *tty) { ... ser->tty = tty_kref_get(tty); ... result = register_netdevice(dev); if (result) { rtnl_unlock(); free_netdev(dev); return -ENODEV; } ... } Ser pointer is netdev private_data, so after free_netdev() this pointer goes away with unputted tty reference. So, fix it by adding tty_kref_put() before freeing netdev. Reported-and-tested-by: syzbot+f303e045423e617d2cad@syzkaller.appspotmail.com Signed-off-by: Pavel Skripkin Signed-off-by: David S. Miller

Merge 5.13-rc4 into tty-next

2021-05-31T07:44:28+00:00

We need the tty/serial fixes in here as well. Signed-off-by: Greg Kroah-Hartman