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authorJiri Slaby <jslaby@suse.cz>2014-05-05 10:24:08 +0200
committerJiri Kosina <jkosina@suse.cz>2014-05-13 10:40:57 +0200
commit9ec28a07c548e804eeaeb0f37450ac5320df10bd (patch)
treea3ffe7a6b039f44ae205c696465be23be929df66
parentb960221f715465be39ef208887de6db4b107bba0 (diff)
n_tty: Fix n_tty_write crash when echoing in raw moderpm-3.0.101-0.29
(bnc#871252 bnc#875690 CVE-2014-0196).
-rw-r--r--patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch76
-rw-r--r--series.conf1
2 files changed, 77 insertions, 0 deletions
diff --git a/patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch b/patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
new file mode 100644
index 0000000000..f4f31ecdee
--- /dev/null
+++ b/patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
@@ -0,0 +1,76 @@
+From: Peter Hurley <peter@hurleysoftware.com>
+Date: Tue, 29 Apr 2014 12:38:36 -0400
+Subject: n_tty: Fix n_tty_write crash when echoing in raw mode
+Patch-mainline: submitted May 5 2014
+References: bnc#871252 bnc#875690 CVE-2014-0196
+
+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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Cc: Linus Torvalds <torvalds@linux-foundation.org>
+Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
+Cc: <stable@vger.kernel.org>
+---
+ drivers/tty/n_tty.c | 2 ++
+ 1 file changed, 2 insertions(+)
+
+--- a/drivers/tty/n_tty.c
++++ b/drivers/tty/n_tty.c
+@@ -2017,7 +2017,9 @@ static ssize_t n_tty_write(struct tty_st
+ 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;
diff --git a/series.conf b/series.conf
index a473ba8de6..e5c5c3a9a5 100644
--- a/series.conf
+++ b/series.conf
@@ -13719,6 +13719,7 @@
##########################################################
patches.suse/revert-U6715-16550A-serial-driver-support.patch
patches.fixes/printk-fix-softlockups-during-heavy-printing.patch
+ patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
########################################################
# Other driver fixes