From 9e6cdbf6fc60f95e232c4ca34004606da9536d01 Mon Sep 17 00:00:00 2001
From: Thomas Graf <tgraf@suug.ch>
Date: Wed, 13 Mar 2013 16:53:07 +0100
Subject: [PATCH] attr: Add nla_nest_cancel() to remove partially added nested
 attributes

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 doc/core.txt           |  1 +
 include/netlink/attr.h |  1 +
 lib/attr.c             | 25 +++++++++++++++++++++++--
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/doc/core.txt b/doc/core.txt
index 8a26dba..1e951d0 100644
--- a/doc/core.txt
+++ b/doc/core.txt
@@ -2316,6 +2316,7 @@ int put_opts(struct nl_msg *msg)
 	return 0;
 
 nla_put_failure:
+	nla_nest_cancel(msg, opts);
 	return -EMSGSIZE;
 }
 --------
diff --git a/include/netlink/attr.h b/include/netlink/attr.h
index 69ecb08..0ed3da3 100644
--- a/include/netlink/attr.h
+++ b/include/netlink/attr.h
@@ -124,6 +124,7 @@ extern int		nla_put_msecs(struct nl_msg *, int, unsigned long);
 extern int		nla_put_nested(struct nl_msg *, int, struct nl_msg *);
 extern struct nlattr *	nla_nest_start(struct nl_msg *, int);
 extern int		nla_nest_end(struct nl_msg *, struct nlattr *);
+extern void		nla_nest_cancel(struct nl_msg *, struct nlattr *);
 extern int		nla_parse_nested(struct nlattr **, int, struct nlattr *,
 					 struct nla_policy *);
 extern int		nla_is_nested(struct nlattr *);
diff --git a/lib/attr.c b/lib/attr.c
index 26bece3..2c03fa1 100644
--- a/lib/attr.c
+++ b/lib/attr.c
@@ -820,8 +820,7 @@ int nla_nest_end(struct nl_msg *msg, struct nlattr *start)
 		 * Kernel can't handle empty nested attributes, trim the
 		 * attribute header again
 		 */
-		msg->nm_nlh->nlmsg_len -= NLA_HDRLEN;
-		memset(nlmsg_tail(msg->nm_nlh), 0, NLA_HDRLEN);
+		nla_nest_cancel(msg, start);
 
 		return 0;
 	}
@@ -849,6 +848,28 @@ int nla_nest_end(struct nl_msg *msg, struct nlattr *start)
 	return 0;
 }
 
+/**
+ * Cancel the addition of a nested attribute
+ * @arg msg		Netlink message
+ * @arg attr		Nested netlink attribute
+ *
+ * Removes any partially added nested Netlink attribute from the message
+ * by resetting the message to the size before the call to nla_nest_start()
+ * and by overwriting any potentially touched message segments with 0.
+ */
+void nla_nest_cancel(struct nl_msg *msg, struct nlattr *attr)
+{
+	ssize_t len;
+
+	len = (void *) nlmsg_tail(msg->nm_nlh) - (void *) attr;
+	if (len < 0)
+		BUG();
+	else if (len > 0) {
+		msg->nm_nlh->nlmsg_len -= len;
+		memset(nlmsg_tail(msg->nm_nlh), 0, len);
+	}
+}
+
 /**
  * Create attribute index based on nested attribute
  * @arg tb		Index array to be filled (maxtype+1 elements).