commit 4ff86df861069e51ee796bac4e8ead942f8985f5
author Hauke Mehrtens <hauke@hauke-m.de> Fri Sep 16 22:40:28 2016 +0200
committer Denys Vlasenko <vda.linux@googlemail.com> Sun Sep 18 22:55:47 2016 +0200
tree cd13a51bb4652cba3fddc3c21d1fc50debbe8e96
parent 0ae0509679033c8c9b511b83027d5ef076b7bf2b

libnetlink: fix alignment of netlink messages

A padding to align a message should not only be added between
different attributes of a netlink message, but also at the end of the
message to pad it to the correct size.

Without this patch the following command does not work and returns an
error code:
ip link add type nlmon

Without this ip from busybox sends this:

sendmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000},
	msg_namelen=12, msg_iov=[{iov_base={{len=45, ...},
		"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\20\0\22\0\t\0\1nlmon"}, iov_len=45}],
	msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 45
return value: 2

The normal ip utile from iproute2 sends this:

sendmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000},
	msg_namelen=12, msg_iov=[{iov_base={{len=48, ...},
		"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\20\0\22\0\t\0\1nlmon\0\0\0"}, iov_len=48}],
	msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 48
return value: 0

With this patch ip from busybox sends this:

sendmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000},
	msg_namelen=12, msg_iov=[{iov_base={{len=48, ...},
		"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\20\0\22\0\t\0\1nlmon\0\0\0"}, iov_len=48}],
	msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 48
return value: 0

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/libiproute/libnetlink.c

diff --git a/networking/libiproute/libnetlink.c b/networking/libiproute/libnetlink.c
index 9d5c641..7e0ff1b 100644
--- a/networking/libiproute/libnetlink.c
+++ b/networking/libiproute/libnetlink.c
@@ -340,14 +340,14 @@
 	int len = RTA_LENGTH(4);
 	struct rtattr *rta;
 
-	if ((int)(NLMSG_ALIGN(n->nlmsg_len) + len) > maxlen) {
+	if ((int)(NLMSG_ALIGN(n->nlmsg_len + len)) > maxlen) {
 		return -1;
 	}
 	rta = (struct rtattr*)(((char*)n) + NLMSG_ALIGN(n->nlmsg_len));
 	rta->rta_type = type;
 	rta->rta_len = len;
 	move_to_unaligned32(RTA_DATA(rta), data);
-	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + len;
+	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len + len);
 	return 0;
 }
 
@@ -356,14 +356,14 @@
 	int len = RTA_LENGTH(alen);
 	struct rtattr *rta;
 
-	if ((int)(NLMSG_ALIGN(n->nlmsg_len) + len) > maxlen) {
+	if ((int)(NLMSG_ALIGN(n->nlmsg_len + len)) > maxlen) {
 		return -1;
 	}
 	rta = (struct rtattr*)(((char*)n) + NLMSG_ALIGN(n->nlmsg_len));
 	rta->rta_type = type;
 	rta->rta_len = len;
 	memcpy(RTA_DATA(rta), data, alen);
-	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + len;
+	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len + len);
 	return 0;
 }
 
@@ -372,14 +372,14 @@
 	int len = RTA_LENGTH(4);
 	struct rtattr *subrta;
 
-	if (RTA_ALIGN(rta->rta_len) + len > maxlen) {
+	if (RTA_ALIGN(rta->rta_len + len) > maxlen) {
 		return -1;
 	}
 	subrta = (struct rtattr*)(((char*)rta) + RTA_ALIGN(rta->rta_len));
 	subrta->rta_type = type;
 	subrta->rta_len = len;
 	move_to_unaligned32(RTA_DATA(subrta), data);
-	rta->rta_len = NLMSG_ALIGN(rta->rta_len) + len;
+	rta->rta_len = NLMSG_ALIGN(rta->rta_len + len);
 	return 0;
 }
 
@@ -388,14 +388,14 @@
 	struct rtattr *subrta;
 	int len = RTA_LENGTH(alen);
 
-	if (RTA_ALIGN(rta->rta_len) + len > maxlen) {
+	if (RTA_ALIGN(rta->rta_len + len) > maxlen) {
 		return -1;
 	}
 	subrta = (struct rtattr*)(((char*)rta) + RTA_ALIGN(rta->rta_len));
 	subrta->rta_type = type;
 	subrta->rta_len = len;
 	memcpy(RTA_DATA(subrta), data, alen);
-	rta->rta_len = NLMSG_ALIGN(rta->rta_len) + len;
+	rta->rta_len = NLMSG_ALIGN(rta->rta_len + len);
 	return 0;
 }