audit: added capacity and reserve() to nlmsg

src/lxc/nl.c

@@ -37,7 +37,7 @@
 
 extern size_t nlmsg_len(const struct nlmsg *nlmsg)
 {
-	return nlmsg->nlmsghdr.nlmsg_len - NLMSG_HDRLEN;
+	return nlmsg->nlmsghdr->nlmsg_len - NLMSG_HDRLEN;
 }
 
 extern void *nlmsg_data(struct nlmsg *nlmsg)
@@ -53,13 +53,16 @@ static int nla_put(struct nlmsg *nlmsg, int attr,
 {
 	struct rtattr *rta;
 	size_t rtalen = RTA_LENGTH(len);
+	size_t tlen = NLMSG_ALIGN(nlmsg->nlmsghdr->nlmsg_len) + RTA_ALIGN(rtalen);
 	
-        rta = NLMSG_TAIL(&nlmsg->nlmsghdr);
-        rta->rta_type = attr;
-        rta->rta_len = rtalen;
-        memcpy(RTA_DATA(rta), data, len);
-        nlmsg->nlmsghdr.nlmsg_len =
-		NLMSG_ALIGN(nlmsg->nlmsghdr.nlmsg_len) + RTA_ALIGN(rtalen);
+	if (tlen > nlmsg->cap)
+		return -ENOMEM;
+
+	rta = NLMSG_TAIL(nlmsg->nlmsghdr);
+	rta->rta_type = attr;
+	rta->rta_len = rtalen;
+	memcpy(RTA_DATA(rta), data, len);
+	nlmsg->nlmsghdr->nlmsg_len = tlen;
 	return 0;
 }
 
@@ -91,7 +94,7 @@ extern int nla_put_attr(struct nlmsg *nlmsg, int attr)
 
 struct rtattr *nla_begin_nested(struct nlmsg *nlmsg, int attr)
 {
-	struct rtattr *rtattr = NLMSG_TAIL(&nlmsg->nlmsghdr);
+	struct rtattr *rtattr = NLMSG_TAIL(nlmsg->nlmsghdr);
 
 	if (nla_put_attr(nlmsg, attr))
 		return NULL;
@@ -101,7 +104,7 @@ struct rtattr *nla_begin_nested(struct nlmsg *nlmsg, int attr)
 
 void nla_end_nested(struct nlmsg *nlmsg, struct rtattr *attr)
 {
-	attr->rta_len = (void *)NLMSG_TAIL(&nlmsg->nlmsghdr) - (void *)attr;
+	attr->rta_len = (void *)NLMSG_TAIL(nlmsg->nlmsghdr) - (void *)attr;
 }
 
 extern struct nlmsg *nlmsg_alloc(size_t size)
@@ -109,18 +112,48 @@ extern struct nlmsg *nlmsg_alloc(size_t size)
 	struct nlmsg *nlmsg;
 	size_t len = NLMSG_HDRLEN + NLMSG_ALIGN(size);
 
-	nlmsg = (struct nlmsg *)malloc(len);
+	nlmsg = (struct nlmsg *)malloc(sizeof(struct nlmsg));
 	if (!nlmsg)
 		return NULL;
 
-	memset(nlmsg, 0, len);
-	nlmsg->nlmsghdr.nlmsg_len = NLMSG_HDRLEN;
+	nlmsg->nlmsghdr = (struct nlmsghdr *)malloc(len);
+	if (!nlmsg->nlmsghdr)
+		goto errout;
+
+	memset(nlmsg->nlmsghdr, 0, len);
+	nlmsg->cap = len;
+	nlmsg->nlmsghdr->nlmsg_len = NLMSG_HDRLEN;
 
 	return nlmsg;
+errout:
+	free(nlmsg);
+	return NULL;
+}
+
+extern void *nlmsg_reserve(struct nlmsg *nlmsg, size_t len)
+{
+	void *buf;
+	size_t nlmsg_len = nlmsg->nlmsghdr->nlmsg_len;
+	size_t tlen = NLMSG_ALIGN(len);
+
+	if (nlmsg_len + tlen > nlmsg->cap)
+		return NULL;
+
+	buf = nlmsg->nlmsghdr + nlmsg_len;
+	nlmsg->nlmsghdr->nlmsg_len += tlen;
+
+	if (tlen > len)
+		memset(buf + len, 0, tlen - len);
+
+	return buf;
 }
 
 extern void nlmsg_free(struct nlmsg *nlmsg)
 {
+	if (!nlmsg)
+		return;
+
+	free(nlmsg->nlmsghdr);
 	free(nlmsg);
 }
 
@@ -130,7 +163,7 @@ extern int netlink_rcv(struct nl_handler *handler, struct nlmsg *answer)
         struct sockaddr_nl nladdr;
         struct iovec iov = {
                 .iov_base = answer,
-                .iov_len = answer->nlmsghdr.nlmsg_len,
+                .iov_len = answer->nlmsghdr->nlmsg_len,
         };
 	
 	struct msghdr msg = {
@@ -157,7 +190,7 @@ again:
 		return 0;
 
 	if (msg.msg_flags & MSG_TRUNC &&
-	    ret == answer->nlmsghdr.nlmsg_len)
+	    ret == answer->nlmsghdr->nlmsg_len)
 		return -EMSGSIZE;
 
 	return ret;
@@ -168,7 +201,7 @@ extern int netlink_send(struct nl_handler *handler, struct nlmsg *nlmsg)
         struct sockaddr_nl nladdr;
         struct iovec iov = {
                 .iov_base = (void*)nlmsg,
-                .iov_len = nlmsg->nlmsghdr.nlmsg_len,
+                .iov_len = nlmsg->nlmsghdr->nlmsg_len,
         };
 	struct msghdr msg = {
                 .msg_name = &nladdr,
@@ -206,7 +239,7 @@ extern int netlink_transaction(struct nl_handler *handler,
 	if (ret < 0)
 		return ret;
 
-	if (answer->nlmsghdr.nlmsg_type == NLMSG_ERROR) {
+	if (answer->nlmsghdr->nlmsg_type == NLMSG_ERROR) {
 		struct nlmsgerr *err = (struct nlmsgerr*)NLMSG_DATA(answer);
 		return err->error;
 	}

src/lxc/nl.h

@@ -53,14 +53,16 @@ struct nl_handler {
 };
 
 /*
- * struct nlmsg : the netlink message structure, it consists just
- *  on a definition for a nlmsghdr. This message is to be used to
+ * struct nlmsg : the netlink message structure. This message is to be used to
  *  be allocated with netlink_alloc.
- * @nlmsghdr : a pointer to a netlink message header, this field
- *   _must_ be always the first field of this structure
+ *
+ * @nlmsghdr: a pointer to a netlink message header
+ * @cap: capacity of the netlink message, this is the initially allocated size
+ * 		and later operations (e.g. reserve and put) can not exceed this limit.
  */
 struct nlmsg {
-	struct nlmsghdr nlmsghdr;
+	struct nlmsghdr *nlmsghdr;
+	ssize_t cap;
 };
 
 /*
@@ -220,6 +222,16 @@ void nla_end_nested(struct nlmsg *nlmsg, struct rtattr *attr);
 struct nlmsg *nlmsg_alloc(size_t size);
 
 /*
+ * Reserve room for additional data at the tail of a netlink message
+ *
+ * @nlmsg: the netlink message
+ * @len: length of additional data to reserve room for
+ *
+ * Returns a pointer to newly reserved room or NULL
+ */
+void *nlmsg_reserve(struct nlmsg *nlmsg, size_t len);
+
+/*
  * nlmsg_free : free a previously allocate message
  *
  * @nlmsg: the netlink message to be freed