[3.8.y.z extended stable] Patch "x86, x32: Correct invalid use of user timespec in the kernel" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86, x32: Correct invalid use of user timespec in the kernel

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.17.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 3ddcb82e957265b049ffcf92c6a27dbae25e5945 Mon Sep 17 00:00:00 2001
From: PaX Team <pageexec at freemail.hu>
Date: Thu, 30 Jan 2014 16:59:25 -0800
Subject: x86, x32: Correct invalid use of user timespec in the kernel

commit 2def2ef2ae5f3990aabdbe8a755911902707d268 upstream.

The x32 case for the recvmsg() timout handling is broken:

  asmlinkage long compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
                                      unsigned int vlen, unsigned int flags,
                                      struct compat_timespec __user *timeout)
  {
          int datagrams;
          struct timespec ktspec;

          if (flags & MSG_CMSG_COMPAT)
                  return -EINVAL;

          if (COMPAT_USE_64BIT_TIME)
                  return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
                                        flags | MSG_CMSG_COMPAT,
                                        (struct timespec *) timeout);
          ...

The timeout pointer parameter is provided by userland (hence the __user
annotation) but for x32 syscalls it's simply cast to a kernel pointer
and is passed to __sys_recvmmsg which will eventually directly
dereference it for both reading and writing.  Other callers to
__sys_recvmmsg properly copy from userland to the kernel first.

The bug was introduced by commit ee4fa23c4bfc ("compat: Use
COMPAT_USE_64BIT_TIME in net/compat.c") and should affect all kernels
since 3.4 (and perhaps vendor kernels if they backported x32 support
along with this code).

Note that CONFIG_X86_X32_ABI gets enabled at build time and only if
CONFIG_X86_X32 is enabled and ld can build x32 executables.

Other uses of COMPAT_USE_64BIT_TIME seem fine.

This addresses CVE-2014-0038.

Signed-off-by: PaX Team <pageexec at freemail.hu>
Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/compat.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/net/compat.c b/net/compat.c
index dd32e34..f50161f 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -780,21 +780,16 @@ asmlinkage long compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
 	if (flags & MSG_CMSG_COMPAT)
 		return -EINVAL;

-	if (COMPAT_USE_64BIT_TIME)
-		return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
-				      flags | MSG_CMSG_COMPAT,
-				      (struct timespec *) timeout);
-
 	if (timeout == NULL)
 		return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
 				      flags | MSG_CMSG_COMPAT, NULL);

-	if (get_compat_timespec(&ktspec, timeout))
+	if (compat_get_timespec(&ktspec, timeout))
 		return -EFAULT;

 	datagrams = __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
 				   flags | MSG_CMSG_COMPAT, &ktspec);
-	if (datagrams > 0 && put_compat_timespec(&ktspec, timeout))
+	if (datagrams > 0 && compat_put_timespec(&ktspec, timeout))
 		datagrams = -EFAULT;

 	return datagrams;
--
1.8.3.2