[kernel/f20] CVE-2014-0196 pty race leading to memory corruption (rhbz 1094232 1094240)

[Josh Boyer]

commit 34d445d5825fc3f7318e6c8b1f7d8935e3f2a752
Author: Josh Boyer <jwboyer at fedoraproject.org>
Date:   Tue May 6 08:35:07 2014 -0400

    CVE-2014-0196 pty race leading to memory corruption (rhbz 1094232 1094240)

 kernel.spec                                        |    7 ++
 ..._tty_write-crash-when-echoing-in-raw-mode.patch |   86 ++++++++++++++++++++
 2 files changed, 93 insertions(+), 0 deletions(-)
---
diff --git a/kernel.spec b/kernel.spec
index 52b10b7..d93ca54 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -769,6 +769,9 @@ Patch25074: 0001-acpi-video-Add-use_native_backlight-quirks-for-Think.patch
 #rhbz 1082586
 Patch25075: locks-allow-__break_lease-to-sleep-even-when-break_t.patch
 
+#CVE-2014-0196 rhbz 1094232 1094240
+Patch25076: n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
+
 # END OF PATCH DEFINITIONS
 
 %endif
@@ -1491,6 +1494,9 @@ ApplyPatch 0001-acpi-video-Add-use_native_backlight-quirks-for-Think.patch
 #rhbz 1082586
 ApplyPatch locks-allow-__break_lease-to-sleep-even-when-break_t.patch
 
+#CVE-2014-0196 rhbz 1094232 1094240
+ApplyPatch n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
+
 # END OF PATCH APPLICATIONS
 
 %endif
@@ -2303,6 +2309,7 @@ fi
 #                 ||     ||
 %changelog
 * Tue May 06 2014 Josh Boyer <jwboyer at fedoraproject.org>
+- CVE-2014-0196 pty race leading to memory corruption (rhbz 1094232 1094240)
 - Add patch to fix smdb soft-lockup (rhbz 1082586)
 
 * Mon May 05 2014 Hans de Goede <hdegoede at redhat.com>
diff --git a/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch b/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
new file mode 100644
index 0000000..d5f980c
--- /dev/null
+++ b/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch
@@ -0,0 +1,86 @@
+Bugzilla: 1094240
+Upstream-status: 3.15 and CC'd to stable
+
+From 4291086b1f081b869c6d79e5b7441633dc3ace00 Mon Sep 17 00:00:00 2001
+From: Peter Hurley <peter at 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 at suse.cz>
+Signed-off-by: Peter Hurley <peter at hurleysoftware.com>
+Signed-off-by: Jiri Slaby <jslaby at suse.cz>
+Cc: Linus Torvalds <torvalds at linux-foundation.org>
+Cc: Alan Cox <alan at lxorguk.ukuu.org.uk>
+Cc: <stable at vger.kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh at 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 41fe8a047d37..fe9d129c8735 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;
+-- 
+1.9.0
+