[3.16.y-ckt stable] Patch "net: socket: Fix the wrong returns for recvmsg and sendmsg" 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: socket: Fix the wrong returns for recvmsg and sendmsg

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/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt13.

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 a45424f25febec0f055dc3fd80e90273edd1f8f6 Mon Sep 17 00:00:00 2001
From: Junling Zheng <zhengjunling at huawei.com>
Date: Mon, 1 Jun 2015 09:28:00 +0000
Subject: net: socket: Fix the wrong returns for recvmsg and sendmsg

Based on 08adb7dabd4874cc5666b4490653b26534702ce0 upstream.

Commit 281c9c36 (net: compat: Update get_compat_msghdr() to match
copy_msghdr_from_user() behaviour) made get_compat_msghdr() return
error if msg_sys->msg_namelen was negative, which changed the behaviors
of recvmsg and sendmsg syscall in a lib32 system:

Before commit 281c9c36, get_compat_msghdr() wouldn't fail and it would
return -EINVAL in move_addr_to_user() or somewhere if msg_sys->msg_namelen
was invalid and then syscall returned -EINVAL, which is correct.

And now, when msg_sys->msg_namelen is negative, get_compat_msghdr() will
fail and wants to return -EINVAL, however, the outer syscall will return
-EFAULT directly, which is unexpected.

This patch gets the return value of get_compat_msghdr() as well as
copy_msghdr_from_user(), then returns this expected value if
get_compat_msghdr() fails.

Fixes: 281c9c36 (net: compat: Update get_compat_msghdr() to match copy_msghdr_from_user() behaviour)
Signed-off-by: Junling Zheng <zhengjunling at huawei.com>
Signed-off-by: Hanbing Xu <xuhanbing at huawei.com>
Cc: Li Zefan <lizefan at huawei.com>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: David Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/socket.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/net/socket.c b/net/socket.c
index 4980af97d87c..fc7ba8cabb72 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2011,14 +2011,12 @@ static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
 	int err, ctl_len, total_len;

 	err = -EFAULT;
-	if (MSG_CMSG_COMPAT & flags) {
-		if (get_compat_msghdr(msg_sys, msg_compat))
-			return -EFAULT;
-	} else {
+	if (MSG_CMSG_COMPAT & flags)
+		err = get_compat_msghdr(msg_sys, msg_compat);
+	else
 		err = copy_msghdr_from_user(msg_sys, msg);
-		if (err)
-			return err;
-	}
+	if (err)
+		return err;

 	if (msg_sys->msg_iovlen > UIO_FASTIOV) {
 		err = -EMSGSIZE;
@@ -2223,14 +2221,12 @@ static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
 	struct sockaddr __user *uaddr;
 	int __user *uaddr_len;

-	if (MSG_CMSG_COMPAT & flags) {
-		if (get_compat_msghdr(msg_sys, msg_compat))
-			return -EFAULT;
-	} else {
+	if (MSG_CMSG_COMPAT & flags)
+		err = get_compat_msghdr(msg_sys, msg_compat);
+	else
 		err = copy_msghdr_from_user(msg_sys, msg);
-		if (err)
-			return err;
-	}
+	if (err)
+		return err;

 	if (msg_sys->msg_iovlen > UIO_FASTIOV) {
 		err = -EMSGSIZE;