diff options
Diffstat (limited to 'kernels/linux-libre-lts-knock/0001-n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch')
| -rw-r--r-- | kernels/linux-libre-lts-knock/0001-n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/kernels/linux-libre-lts-knock/0001-n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch b/kernels/linux-libre-lts-knock/0001-n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch new file mode 100644 index 000000000..cb659dc7d --- /dev/null +++ b/kernels/linux-libre-lts-knock/0001-n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch @@ -0,0 +1,83 @@ +From 4291086b1f081b869c6d79e5b7441633dc3ace00 Mon Sep 17 00:00:00 2001 +From: Peter Hurley <peter@hurleysoftware.com> +Date: Sat, 3 May 2014 14:04:59 +0200 +Subject: [PATCH] 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 + +References: CVE-2014-0196 +Reported-and-tested-by: Jiri Slaby <jslaby@suse.cz> +Signed-off-by: Peter Hurley <peter@hurleysoftware.com> +Signed-off-by: Jiri Slaby <jslaby@suse.cz> +Cc: Linus Torvalds <torvalds@linux-foundation.org> +Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> +Cc: <stable@vger.kernel.org> +Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +--- + drivers/tty/n_tty.c | 4 ++++ + 1 file changed, 4 insertions(+) + +diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c +index 41fe8a0..fe9d129 100644 +--- a/drivers/tty/n_tty.c ++++ b/drivers/tty/n_tty.c +@@ -2353,8 +2353,12 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, + if (tty->ops->flush_chars) + tty->ops->flush_chars(tty); + } else { ++ struct n_tty_data *ldata = tty->disc_data; ++ + while (nr > 0) { ++ mutex_lock(&ldata->output_lock); + c = tty->ops->write(tty, b, nr); ++ mutex_unlock(&ldata->output_lock); + if (c < 0) { + retval = c; + goto break_out; +-- +1.9.2 + |