[3.16.y-ckt stable] Patch "net: compat: Ignore MSG_CMSG_COMPAT in compat_sys_{send, recv}msg" has been added to staging queue

[Luis Henriques]

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

    net: compat: Ignore MSG_CMSG_COMPAT in compat_sys_{send, recv}msg

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt9.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 1621c90eaeeddb60a183338c677ea0dd4d9f19fe Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas at arm.com>
Date: Mon, 23 Feb 2015 18:12:56 +0000
Subject: net: compat: Ignore MSG_CMSG_COMPAT in compat_sys_{send, recv}msg

commit d720d8cec563ce4e4fa44a613d4f2dcb1caf2998 upstream.

With commit a7526eb5d06b (net: Unbreak compat_sys_{send,recv}msg), the
MSG_CMSG_COMPAT flag is blocked at the compat syscall entry points,
changing the kernel compat behaviour from the one before the commit it
was trying to fix (1be374a0518a, net: Block MSG_CMSG_COMPAT in
send(m)msg and recv(m)msg).

On 32-bit kernels (!CONFIG_COMPAT), MSG_CMSG_COMPAT is 0 and the native
32-bit sys_sendmsg() allows flag 0x80000000 to be set (it is ignored by
the kernel). However, on a 64-bit kernel, the compat ABI is different
with commit a7526eb5d06b.

This patch changes the compat_sys_{send,recv}msg behaviour to the one
prior to commit 1be374a0518a.

The problem was found running 32-bit LTP (sendmsg01) binary on an arm64
kernel. Arguably, LTP should not pass 0xffffffff as flags to sendmsg()
but the general rule is not to break user ABI (even when the user
behaviour is not entirely sane).

Fixes: a7526eb5d06b (net: Unbreak compat_sys_{send,recv}msg)
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: David S. Miller <davem at davemloft.net>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/compat.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/net/compat.c b/net/compat.c
index bc8aeefddf3f..c48930373e65 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -738,24 +738,18 @@ static unsigned char nas[21] = {

 COMPAT_SYSCALL_DEFINE3(sendmsg, int, fd, struct compat_msghdr __user *, msg, unsigned int, flags)
 {
-	if (flags & MSG_CMSG_COMPAT)
-		return -EINVAL;
 	return __sys_sendmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
 }

 COMPAT_SYSCALL_DEFINE4(sendmmsg, int, fd, struct compat_mmsghdr __user *, mmsg,
 		       unsigned int, vlen, unsigned int, flags)
 {
-	if (flags & MSG_CMSG_COMPAT)
-		return -EINVAL;
 	return __sys_sendmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
 			      flags | MSG_CMSG_COMPAT);
 }

 COMPAT_SYSCALL_DEFINE3(recvmsg, int, fd, struct compat_msghdr __user *, msg, unsigned int, flags)
 {
-	if (flags & MSG_CMSG_COMPAT)
-		return -EINVAL;
 	return __sys_recvmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
 }

@@ -778,9 +772,6 @@ COMPAT_SYSCALL_DEFINE5(recvmmsg, int, fd, struct compat_mmsghdr __user *, mmsg,
 	int datagrams;
 	struct timespec ktspec;

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