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>

1 files changed, 8 insertions, 8 deletions

diff --git a/networking/libiproute/libnetlink.c b/networking/libiproute/libnetlink.c
index 9d5c6416b..7e0ff1b6c 100644
--- a/networking/libiproute/libnetlink.c
+++ b/networking/libiproute/libnetlink.c
@@ -340,14 +340,14 @@ int FAST_FUNC addattr32(struct nlmsghdr *n, int maxlen, int type, uint32_t data)
         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 FAST_FUNC addattr_l(struct nlmsghdr *n, int maxlen, int type, void *data, in
         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 FAST_FUNC rta_addattr32(struct rtattr *rta, int maxlen, int type, uint32_t d
         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 @@ int FAST_FUNC rta_addattr_l(struct rtattr *rta, int maxlen, int type, void *data
         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;
 }