[PATCH SECURITY 1/1] x86, x32: Correct invalid use of user timespec in the kernel

["H. Peter Anvin" <hpa@xxxxxxxxx>]

From: "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>

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
http://git.kernel.org/linus/ee4fa23c4b (other uses of
COMPAT_USE_64BIT_TIME seem fine) 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.

This addresses CVE-2014-0038.

Signed-off-by: PaX Team <pageexec@xxxxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v3.4+
---
 net/compat.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/net/compat.c b/net/compat.c
index dd32e34c1e2c..f50161fb812e 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;
-- 
1.8.3.1

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