mirror of
https://github.com/Divested-Mobile/DivestOS-Build.git
synced 2024-12-11 08:54:28 -05:00
84 lines
3.1 KiB
Diff
84 lines
3.1 KiB
Diff
|
From 9aabfc9e7775abbbcf534cdecccc4f12ee423b27 Mon Sep 17 00:00:00 2001
|
||
|
|
From: Peter Hurley <peter@hurleysoftware.com>
|
||
|
|
Date: Tue, 13 May 2014 14:36:46 -0700
|
||
|
|
Subject: n_tty: Fix n_tty_write crash when echoing in raw mode
|
||
|
|
|
||
|
|
The tty atomic_write_lock does not provide an exclusion guarantee for
|
||
|
|
the tty driver if the termios settings are LECHO & !OPOST. And since
|
||
|
|
it is unexpected and not allowed to call TTY buffer helpers like
|
||
|
|
tty_insert_flip_string concurrently, this may lead to crashes when
|
||
|
|
concurrect writers call pty_write. In that case the following two
|
||
|
|
writers:
|
||
|
|
* the ECHOing from a workqueue and
|
||
|
|
* pty_write from the process
|
||
|
|
race and can overflow the corresponding TTY buffer like follows.
|
||
|
|
|
||
|
|
If we look into tty_insert_flip_string_fixed_flag, there is:
|
||
|
|
int space = __tty_buffer_request_room(port, goal, flags);
|
||
|
|
struct tty_buffer *tb = port->buf.tail;
|
||
|
|
...
|
||
|
|
memcpy(char_buf_ptr(tb, tb->used), chars, space);
|
||
|
|
...
|
||
|
|
tb->used += space;
|
||
|
|
|
||
|
|
so the race of the two can result in something like this:
|
||
|
|
A B
|
||
|
|
__tty_buffer_request_room
|
||
|
|
__tty_buffer_request_room
|
||
|
|
memcpy(buf(tb->used), ...)
|
||
|
|
tb->used += space;
|
||
|
|
memcpy(buf(tb->used), ...) ->BOOM
|
||
|
|
|
||
|
|
B's memcpy is past the tty_buffer due to the previous A's tb->used
|
||
|
|
increment.
|
||
|
|
|
||
|
|
Since the N_TTY line discipline input processing can output
|
||
|
|
concurrently with a tty write, obtain the N_TTY ldisc output_lock to
|
||
|
|
serialize echo output with normal tty writes. This ensures the tty
|
||
|
|
buffer helper tty_insert_flip_string is not called concurrently and
|
||
|
|
everything is fine.
|
||
|
|
|
||
|
|
Note that this is nicely reproducible by an ordinary user using
|
||
|
|
forkpty and some setup around that (raw termios + ECHO). And it is
|
||
|
|
present in kernels at least after commit
|
||
|
|
d945cb9cce20ac7143c2de8d88b187f62db99bdc (pty: Rework the pty layer to
|
||
|
|
use the normal buffering logic) in 2.6.31-rc3.
|
||
|
|
|
||
|
|
js: add more info to the commit log
|
||
|
|
js: switch to bool
|
||
|
|
js: lock unconditionally
|
||
|
|
js: lock only the tty->ops->write call
|
||
|
|
|
||
|
|
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
|
||
|
|
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
|
||
|
|
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
|
||
|
|
Change-Id: I9e235db6ec2bb950f26bd8a23f6145dab5dc0a15
|
||
|
|
Git-commit: 4291086b1f081b869c6d79e5b7441633dc3ace00
|
||
|
|
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
|
||
|
|
Signed-off-by: Avijit Kanti Das <avijitnsec@codeaurora.org>
|
||
|
|
[rsiddoji@codeaurora.org: resolve trivial merge conflicts]
|
||
|
|
Signed-off-by: Ravi Kumar S <rsiddoji@codeaurora.org>
|
||
|
|
---
|
||
|
|
drivers/tty/n_tty.c | 3 +++
|
||
|
|
1 file changed, 3 insertions(+)
|
||
|
|
|
||
|
|
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
|
||
|
|
index 8eb5573..54c46c8 100644
|
||
|
|
--- a/drivers/tty/n_tty.c
|
||
|
|
+++ b/drivers/tty/n_tty.c
|
||
|
|
@@ -1998,8 +1998,11 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
|
||
|
|
if (tty->ops->flush_chars)
|
||
|
|
tty->ops->flush_chars(tty);
|
||
|
|
} else {
|
||
|
|
+
|
||
|
|
while (nr > 0) {
|
||
|
|
+ mutex_lock(&tty->output_lock);
|
||
|
|
c = tty->ops->write(tty, b, nr);
|
||
|
|
+ mutex_unlock(&tty->output_lock);
|
||
|
|
if (c < 0) {
|
||
|
|
retval = c;
|
||
|
|
goto break_out;
|
||
|
|
--
|
||
|
|
cgit v1.1
|
||
|
|
|