commit a501ab75e7624d133a5a3c7ec010687c8b961d23 upstream.

There is a race in pty_write(). pty_write() can be called in parallel
with e.g. ioctl(TIOCSTI) or ioctl(TCXONC) which also inserts chars to
the buffer. Provided, tty_flip_buffer_push() in pty_write() is called
outside the lock, it can commit inconsistent tail. This can lead to out
of bounds writes and other issues. See the Link below.

To fix this, we have to introduce a new helper called
tty_insert_flip_string_and_push_buffer(). It does both
tty_insert_flip_string() and tty_flip_buffer_commit() under the port
lock. It also calls queue_work(), but outside the lock. See
71a174b39f10 (pty: do tty_flip_buffer_push without port->lock in
pty_write) for the reasons.

Keep the helper internal-only (in drivers' tty.h). It is not intended to
be used widely.

Link: https://seclists.org/oss-sec/2022/q2/155
Fixes: 71a174b39f10 (pty: do tty_flip_buffer_push without port->lock in pty_write)
Cc: 一只狗 <chennbnbnb@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220707082558.9250-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit 5db96ef23bda6c2a61a51693c85b78b52d03f654 upstream.

Since commit a9c3f68f3cd8d (tty: Fix low_latency BUG) in 2014,
tty_flip_buffer_push() is only a wrapper to tty_schedule_flip(). All
users were converted in the previous patches, so remove
tty_schedule_flip() completely while inlining its body into
tty_flip_buffer_push().

One less exported function.

Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20211122111648.30379-4-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit 979990c6284814617d8f2179d197f72ff62b5d85 upstream.

kernelci.org reports a crazy stack usage for the VT code when CONFIG_KASAN
is enabled:

drivers/tty/vt/keyboard.c: In function 'kbd_keycode':
drivers/tty/vt/keyboard.c:1452:1: error: the frame size of 2240 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

The problem is that tty_insert_flip_char() gets inlined many times into
kbd_keycode(), and also into other functions, and each copy requires 128
bytes for stack redzone to check for a possible out-of-bounds access on
the 'ch' and 'flags' arguments that are passed into
tty_insert_flip_string_flags as a variable-length string.

This introduces a new __tty_insert_flip_char() function for the slow
path, which receives the two arguments by value. This completely avoids
the problem and the stack usage goes back down to around 100 bytes.

Without KASAN, this is also slightly better, as we don't have to
spill the arguments to the stack but can simply pass 'ch' and 'flag'
in registers, saving a few bytes in .text for each call site.

This should be backported to linux-4.0 or later, which first introduced
the stack sanitizer in the kernel.

Fixes: c420f167db8c ("kasan: enable stack instrumentation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tty flip buffers use GFP_ATOMIC allocations for received data
which is to be processed by the line discipline. For each byte
received, an extra byte is used to indicate the error status of
that byte.

Instead, if the received data is error-free, encode the entire
buffer without status bytes.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

There is no in-tree user of tty_prepare_flip_string_flags(); remove.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Allow driver to configure its maximum flip buffer memory
consumption/limit. This is necessary for very-high speed line
rates (in excess of 10MB/sec) because the flip buffers can
be saturated before the line discipline has a chance to
throttle the input.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Convert the tty_buffer_flush() exclusion mechanism to a
public interface - tty_buffer_lock/unlock_exclusive() - and use
the interface to safely write the paste selection to the line
discipline.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Lockless flip buffers require atomically updating the bytes-in-use
watermark.

The pty driver also peeks at the watermark value to limit
memory consumption to a much lower value than the default; query
the watermark with new fn, tty_buffer_space_avail().

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The char_buf_ptr and flag_buf_ptr values are trivially derived from
the .data field offset; compute values as needed.

Fixes a long-standing type-mismatch with the char and flag ptrs.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Now, we start converting tty buffer functions to actually use
tty_port. This will allow us to get rid of the need of tty in many
call sites. Only tty_port will needed and hence no more
tty_port_tty_get in those paths.

This is the last one: tty_schedule_flip

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>