Merge tag 'tty-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty/serial updates from Greg KH:
"Here is the big set of tty/serial driver changes for 6.19-rc1. Nothing

Merge tag 'tty-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

Pull tty/serial updates from Greg KH:
"Here is the big set of tty/serial driver changes for 6.19-rc1. Nothing
major at all, just small constant churn to make the tty layer
"cleaner" as well as serial driver updates and even a new test added!
Included in here are:

- More tty/serial cleanups from Jiri

- tty tiocsti test added to hopefully ensure we don't regress in this
area again

- sc16is7xx driver updates

- imx serial driver updates

- 8250 driver updates

- new hardware device ids added

- other minor serial/tty driver cleanups and tweaks

All of these have been in linux-next for a while with no reported
issues"

* tag 'tty-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (60 commits)
serial: sh-sci: Fix deadlock during RSCI FIFO overrun error
dt-bindings: serial: rsci: Drop "uart-has-rtscts: false"
LoongArch: dts: Add uart new compatible string
serial: 8250: Add Loongson uart driver support
dt-bindings: serial: 8250: Add Loongson uart compatible
serial: 8250: add driver for KEBA UART
serial: Keep rs485 settings for devices without firmware node
serial: qcom-geni: Enable Serial on SA8255p Qualcomm platforms
serial: qcom-geni: Enable PM runtime for serial driver
serial: sprd: Return -EPROBE_DEFER when uart clock is not ready
tty: serial: samsung: Declare earlycon for Exynos850
serial: icom: Convert PCIBIOS_* return codes to errnos
serial: 8250-of: Fix style issues in 8250_of.c
serial: add support of CPCI cards
serial: mux: Fix kernel doc for mux_poll()
tty: replace use of system_unbound_wq with system_dfl_wq
serial: 8250_platform: simplify IRQF_SHARED handling
serial: 8250: make share_irqs local to 8250_platform
serial: 8250: move skip_txen_test to core
serial: drop SERIAL_8250_DEPRECATED_OPTIONS
...

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selftests/tty: add TIOCSTI test suite

TIOCSTI is a TTY ioctl command that allows inserting characters into
the terminal input queue, making it appear as if the user typed those
characters. This func

selftests/tty: add TIOCSTI test suite

TIOCSTI is a TTY ioctl command that allows inserting characters into
the terminal input queue, making it appear as if the user typed those
characters. This functionality has behavior that varies based on system
configuration and process credentials.

The dev.tty.legacy_tiocsti sysctl introduced in commit 83efeeeb3d04
("tty: Allow TIOCSTI to be disabled") controls TIOCSTI usage. When
disabled, TIOCSTI requires CAP_SYS_ADMIN capability.

The current implementation checks the current process's credentials via
capable(CAP_SYS_ADMIN), but does not validate against the file opener's
credentials stored in file->f_cred. This creates different behavior when
file descriptors are passed between processes via SCM_RIGHTS.

Add a test suite with 16 test variants using fixture variants to verify
TIOCSTI behavior when dev.tty.legacy_tiocsti is enabled/disabled:

- Basic TIOCSTI tests (8 variants): Direct testing with different
capability and controlling terminal combinations
- FD passing tests (8 variants): Test behavior when file descriptors
are passed between processes with different capabilities

The FD passing tests document this behavior - some tests show different
results than expected based on file opener credentials, demonstrating
that TIOCSTI uses current process credentials rather than file opener
credentials.

The tests validate proper enforcement of the legacy_tiocsti sysctl. Test
implementation uses openpty(3) with TIOCSCTTY for isolated PTY
environments. See tty_ioctl(4) for details on TIOCSTI behavior and
security requirements.

Signed-off-by: Abhinav Saxena <xandfury@gmail.com>
Link: https://patch.msgid.link/20250903-toicsti-bug-v4-1-4894b6649ef8@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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