rtnetlink: Fix message size calculation for link messages

nlmsg_total_size() calculates the length of a netlink message
including header and alignment. nla_total_size() calculates the
space an individual attribute consumes which was meant to be used
in this context.

Also, ensure to account for the attribute header for the
IFLA_INFO_XSTATS attribute as implementations of get_xstats_size()
seem to assume that we do so.

The addition of two message headers minus the missing attribute
header resulted in a calculated message size that was larger than
required. Therefore we never risked running out of skb tailroom.

Signed-off-by: Thomas Graf <tgraf@infradead.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 4 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 8121268ddbdd..841c287ef40a 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -347,16 +347,17 @@ static size_t rtnl_link_get_size(const struct net_device *dev)
         if (!ops)
                 return 0;
 
-        size = nlmsg_total_size(sizeof(struct nlattr)) + /* IFLA_LINKINFO */
-               nlmsg_total_size(strlen(ops->kind) + 1);  /* IFLA_INFO_KIND */
+        size = nla_total_size(sizeof(struct nlattr)) + /* IFLA_LINKINFO */
+               nla_total_size(strlen(ops->kind) + 1);  /* IFLA_INFO_KIND */
 
         if (ops->get_size)
                 /* IFLA_INFO_DATA + nested data */
-                size += nlmsg_total_size(sizeof(struct nlattr)) +
+                size += nla_total_size(sizeof(struct nlattr)) +
                         ops->get_size(dev);
 
         if (ops->get_xstats_size)
-                size += ops->get_xstats_size(dev);      /* IFLA_INFO_XSTATS */
+                /* IFLA_INFO_XSTATS */
+                size += nla_total_size(ops->get_xstats_size(dev));
 
         return size;
 }