netlink: Introduce nla_strdup()

This is similar to strdup() for netlink string attributes.
Signed-off-by: NPhil Sutter <phil@nwl.cc>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

include/net/netlink.h

@@ -247,6 +247,7 @@ int nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
 int nla_policy_len(const struct nla_policy *, int);
 struct nlattr *nla_find(const struct nlattr *head, int len, int attrtype);
 size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize);
+char *nla_strdup(const struct nlattr *nla, gfp_t flags);
 int nla_memcpy(void *dest, const struct nlattr *src, int count);
 int nla_memcmp(const struct nlattr *nla, const void *data, size_t size);
 int nla_strcmp(const struct nlattr *nla, const char *str);

lib/nlattr.c

@@ -271,6 +271,30 @@ size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
 }
 EXPORT_SYMBOL(nla_strlcpy);
 
+/**
+ * nla_strdup - Copy string attribute payload into a newly allocated buffer
+ * @nla: attribute to copy the string from
+ * @flags: the type of memory to allocate (see kmalloc).
+ *
+ * Returns a pointer to the allocated buffer or NULL on error.
+ */
+char *nla_strdup(const struct nlattr *nla, gfp_t flags)
+{
+	size_t srclen = nla_len(nla);
+	char *src = nla_data(nla), *dst;
+
+	if (srclen > 0 && src[srclen - 1] == '\0')
+		srclen--;
+
+	dst = kmalloc(srclen + 1, flags);
+	if (dst != NULL) {
+		memcpy(dst, src, srclen);
+		dst[srclen] = '\0';
+	}
+	return dst;
+}
+EXPORT_SYMBOL(nla_strdup);
+
 /**
  * nla_memcpy - Copy a netlink attribute into another memory area
  * @dest: where to copy to memcpy