[NETLINK]: Type-safe netlink messages/attributes interface

Introduces a new type-safe interface for netlink message and
attributes handling. The interface is fully binary compatible
with the old interface towards userspace. Besides type safety,
this interface features attribute validation capabilities,
simplified message contstruction, and documentation.

The resulting netlink code should be smaller, less error prone
and easier to understand.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netlink.h

@@ -71,7 +71,8 @@ struct nlmsghdr
 
 #define NLMSG_ALIGNTO	4
 #define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )
-#define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(sizeof(struct nlmsghdr)))
+#define NLMSG_HDRLEN	 ((int) NLMSG_ALIGN(sizeof(struct nlmsghdr)))
+#define NLMSG_LENGTH(len) ((len)+NLMSG_ALIGN(NLMSG_HDRLEN))
 #define NLMSG_SPACE(len) NLMSG_ALIGN(NLMSG_LENGTH(len))
 #define NLMSG_DATA(nlh)  ((void*)(((char*)nlh) + NLMSG_LENGTH(0)))
 #define NLMSG_NEXT(nlh,len)	 ((len) -= NLMSG_ALIGN((nlh)->nlmsg_len), \
@@ -86,6 +87,8 @@ struct nlmsghdr
 #define NLMSG_DONE		0x3	/* End of a dump	*/
 #define NLMSG_OVERRUN		0x4	/* Data lost		*/
 
+#define NLMSG_MIN_TYPE		0x10	/* < 0x10: reserved control messages */
+
 struct nlmsgerr
 {
 	int		error;
@@ -108,6 +111,25 @@ enum {
 	NETLINK_CONNECTED,
 };
 
+/*
+ *  <------- NLA_HDRLEN ------> <-- NLA_ALIGN(payload)-->
+ * +---------------------+- - -+- - - - - - - - - -+- - -+
+ * |        Header       | Pad |     Payload       | Pad |
+ * |   (struct nlattr)   | ing |                   | ing |
+ * +---------------------+- - -+- - - - - - - - - -+- - -+
+ *  <-------------- nlattr->nla_len -------------->
+ */
+
+struct nlattr
+{
+	__u16           nla_len;
+	__u16           nla_type;
+};
+
+#define NLA_ALIGNTO		4
+#define NLA_ALIGN(len)		(((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1))
+#define NLA_HDRLEN		((int) NLA_ALIGN(sizeof(struct nlattr)))
+
 #ifdef __KERNEL__
 
 #include <linux/capability.h>

net/netlink/Makefile

@@ -2,4 +2,4 @@
 # Makefile for the netlink driver.
 #
 
-obj-y  				:= af_netlink.o
+obj-y  				:= af_netlink.o attr.o

net/netlink/attr.c

+/*
+ * NETLINK      Netlink attributes
+ *
+ * 		Authors:	Thomas Graf <tgraf@suug.ch>
+ * 				Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/jiffies.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <net/netlink.h>
+
+static u16 nla_attr_minlen[NLA_TYPE_MAX+1] __read_mostly = {
+	[NLA_U8]	= sizeof(u8),
+	[NLA_U16]	= sizeof(u16),
+	[NLA_U32]	= sizeof(u32),
+	[NLA_U64]	= sizeof(u64),
+	[NLA_STRING]	= 1,
+	[NLA_NESTED]	= NLA_HDRLEN,
+};
+
+static int validate_nla(struct nlattr *nla, int maxtype,
+			struct nla_policy *policy)
+{
+	struct nla_policy *pt;
+	int minlen = 0;
+
+	if (nla->nla_type <= 0 || nla->nla_type > maxtype)
+		return 0;
+
+	pt = &policy[nla->nla_type];
+
+	BUG_ON(pt->type > NLA_TYPE_MAX);
+
+	if (pt->minlen)
+		minlen = pt->minlen;
+	else if (pt->type != NLA_UNSPEC)
+		minlen = nla_attr_minlen[pt->type];
+
+	if (pt->type == NLA_FLAG && nla_len(nla) > 0)
+		return -ERANGE;
+
+	if (nla_len(nla) < minlen)
+		return -ERANGE;
+
+	return 0;
+}
+
+/**
+ * nla_validate - Validate a stream of attributes
+ * @head: head of attribute stream
+ * @len: length of attribute stream
+ * @maxtype: maximum attribute type to be expected
+ * @policy: validation policy
+ *
+ * Validates all attributes in the specified attribute stream against the
+ * specified policy. Attributes with a type exceeding maxtype will be
+ * ignored. See documenation of struct nla_policy for more details.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int nla_validate(struct nlattr *head, int len, int maxtype,
+		 struct nla_policy *policy)
+{
+	struct nlattr *nla;
+	int rem, err;
+
+	nla_for_each_attr(nla, head, len, rem) {
+		err = validate_nla(nla, maxtype, policy);
+		if (err < 0)
+			goto errout;
+	}
+
+	err = 0;
+errout:
+	return err;
+}
+
+/**
+ * nla_parse - Parse a stream of attributes into a tb buffer
+ * @tb: destination array with maxtype+1 elements
+ * @maxtype: maximum attribute type to be expected
+ * @head: head of attribute stream
+ * @len: length of attribute stream
+ *
+ * Parses a stream of attributes and stores a pointer to each attribute in
+ * the tb array accessable via the attribute type. Attributes with a type
+ * exceeding maxtype will be silently ignored for backwards compatibility
+ * reasons. policy may be set to NULL if no validation is required.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head, int len,
+	      struct nla_policy *policy)
+{
+	struct nlattr *nla;
+	int rem, err;
+
+	memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
+
+	nla_for_each_attr(nla, head, len, rem) {
+		u16 type = nla->nla_type;
+
+		if (type > 0 && type <= maxtype) {
+			if (policy) {
+				err = validate_nla(nla, maxtype, policy);
+				if (err < 0)
+					goto errout;
+			}
+
+			tb[type] = nla;
+		}
+	}
+
+	if (unlikely(rem > 0))
+		printk(KERN_WARNING "netlink: %d bytes leftover after parsing "
+		       "attributes.\n", rem);
+
+	err = 0;
+errout:
+	return err;
+}
+
+/**
+ * nla_find - Find a specific attribute in a stream of attributes
+ * @head: head of attribute stream
+ * @len: length of attribute stream
+ * @attrtype: type of attribute to look for
+ *
+ * Returns the first attribute in the stream matching the specified type.
+ */
+struct nlattr *nla_find(struct nlattr *head, int len, int attrtype)
+{
+	struct nlattr *nla;
+	int rem;
+
+	nla_for_each_attr(nla, head, len, rem)
+		if (nla->nla_type == attrtype)
+			return nla;
+
+	return NULL;
+}
+
+/**
+ * nla_strlcpy - Copy string attribute payload into a sized buffer
+ * @dst: where to copy the string to
+ * @src: attribute to copy the string from
+ * @dstsize: size of destination buffer
+ *
+ * Copies at most dstsize - 1 bytes into the destination buffer.
+ * The result is always a valid NUL-terminated string. Unlike
+ * strlcpy the destination buffer is always padded out.
+ *
+ * Returns the length of the source buffer.
+ */
+size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
+{
+	size_t srclen = nla_len(nla);
+	char *src = nla_data(nla);
+
+	if (srclen > 0 && src[srclen - 1] == '\0')
+		srclen--;
+
+	if (dstsize > 0) {
+		size_t len = (srclen >= dstsize) ? dstsize - 1 : srclen;
+
+		memset(dst, 0, dstsize);
+		memcpy(dst, src, len);
+	}
+
+	return srclen;
+}
+
+/**
+ * nla_memcpy - Copy a netlink attribute into another memory area
+ * @dest: where to copy to memcpy
+ * @src: netlink attribute to copy from
+ * @count: size of the destination area
+ *
+ * Note: The number of bytes copied is limited by the length of
+ *       attribute's payload. memcpy
+ *
+ * Returns the number of bytes copied.
+ */
+int nla_memcpy(void *dest, struct nlattr *src, int count)
+{
+	int minlen = min_t(int, count, nla_len(src));
+
+	memcpy(dest, nla_data(src), minlen);
+
+	return minlen;
+}
+
+/**
+ * nla_memcmp - Compare an attribute with sized memory area
+ * @nla: netlink attribute
+ * @data: memory area
+ * @size: size of memory area
+ */
+int nla_memcmp(const struct nlattr *nla, const void *data,
+			     size_t size)
+{
+	int d = nla_len(nla) - size;
+
+	if (d == 0)
+		d = memcmp(nla_data(nla), data, size);
+
+	return d;
+}
+
+/**
+ * nla_strcmp - Compare a string attribute against a string
+ * @nla: netlink string attribute
+ * @str: another string
+ */
+int nla_strcmp(const struct nlattr *nla, const char *str)
+{
+	int len = strlen(str) + 1;
+	int d = nla_len(nla) - len;
+
+	if (d == 0)
+		d = memcmp(nla_data(nla), str, len);
+
+	return d;
+}
+
+/**
+ * __nla_reserve - reserve room for attribute on the skb
+ * @skb: socket buffer to reserve room on
+ * @attrtype: attribute type
+ * @attrlen: length of attribute payload
+ *
+ * Adds a netlink attribute header to a socket buffer and reserves
+ * room for the payload but does not copy it.
+ *
+ * The caller is responsible to ensure that the skb provides enough
+ * tailroom for the attribute header and payload.
+ */
+struct nlattr *__nla_reserve(struct sk_buff *skb, int attrtype, int attrlen)
+{
+	struct nlattr *nla;
+
+	nla = (struct nlattr *) skb_put(skb, nla_total_size(attrlen));
+	nla->nla_type = attrtype;
+	nla->nla_len = nla_attr_size(attrlen);
+
+	memset((unsigned char *) nla + nla->nla_len, 0, nla_padlen(attrlen));
+
+	return nla;
+}
+
+/**
+ * nla_reserve - reserve room for attribute on the skb
+ * @skb: socket buffer to reserve room on
+ * @attrtype: attribute type
+ * @attrlen: length of attribute payload
+ *
+ * Adds a netlink attribute header to a socket buffer and reserves
+ * room for the payload but does not copy it.
+ *
+ * Returns NULL if the tailroom of the skb is insufficient to store
+ * the attribute header and payload.
+ */
+struct nlattr *nla_reserve(struct sk_buff *skb, int attrtype, int attrlen)
+{
+	if (unlikely(skb_tailroom(skb) < nla_total_size(attrlen)))
+		return NULL;
+
+	return __nla_reserve(skb, attrtype, attrlen);
+}
+
+/**
+ * __nla_put - Add a netlink attribute to a socket buffer
+ * @skb: socket buffer to add attribute to
+ * @attrtype: attribute type
+ * @attrlen: length of attribute payload
+ * @data: head of attribute payload
+ *
+ * The caller is responsible to ensure that the skb provides enough
+ * tailroom for the attribute header and payload.
+ */
+void __nla_put(struct sk_buff *skb, int attrtype, int attrlen,
+			     const void *data)
+{
+	struct nlattr *nla;
+
+	nla = __nla_reserve(skb, attrtype, attrlen);
+	memcpy(nla_data(nla), data, attrlen);
+}
+
+
+/**
+ * nla_put - Add a netlink attribute to a socket buffer
+ * @skb: socket buffer to add attribute to
+ * @attrtype: attribute type
+ * @attrlen: length of attribute payload
+ * @data: head of attribute payload
+ *
+ * Returns -1 if the tailroom of the skb is insufficient to store
+ * the attribute header and payload.
+ */
+int nla_put(struct sk_buff *skb, int attrtype, int attrlen, const void *data)
+{
+	if (unlikely(skb_tailroom(skb) < nla_total_size(attrlen)))
+		return -1;
+
+	__nla_put(skb, attrtype, attrlen, data);
+	return 0;
+}
+
+
+EXPORT_SYMBOL(nla_validate);
+EXPORT_SYMBOL(nla_parse);
+EXPORT_SYMBOL(nla_find);
+EXPORT_SYMBOL(nla_strlcpy);
+EXPORT_SYMBOL(__nla_reserve);
+EXPORT_SYMBOL(nla_reserve);
+EXPORT_SYMBOL(__nla_put);
+EXPORT_SYMBOL(nla_put);
+EXPORT_SYMBOL(nla_memcpy);
+EXPORT_SYMBOL(nla_memcmp);
+EXPORT_SYMBOL(nla_strcmp);