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

[Luis Henriques]

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-3.5.y-queue branch of the 3.5.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-3.5.y-queue

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

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From c63c867b779896ac23c45a8244cce8f5924099e2 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: Luis Henriques <luis.henriques 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 1d223d5..9c0fca1 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -781,21 +781,16 @@ 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