attr: add put function that allows to check buffer size

This patch adds a set of function that allows to check the
size of the buffer. This is useful for attribute batching.

This is strongly based on a patch from Jozsef.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 192 insertions, 0 deletions

diff --git a/include/libmnl/libmnl.h b/include/libmnl/libmnl.h
index 5b8d78c..1237b6d 100644
--- a/include/libmnl/libmnl.h
+++ b/include/libmnl/libmnl.h
@@ -93,8 +93,18 @@ extern void mnl_attr_put_u64(struct nlmsghdr *nlh, uint16_t type, uint64_t data)
 extern void mnl_attr_put_str(struct nlmsghdr *nlh, uint16_t type, const char *data);
 extern void mnl_attr_put_strz(struct nlmsghdr *nlh, uint16_t type, const char *data);
 
+/* TLV attribute putters with buffer boundary checkings */
+extern bool mnl_attr_put_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, size_t len, const void *data);
+extern bool mnl_attr_put_u8_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, uint8_t data);
+extern bool mnl_attr_put_u16_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, uint16_t data);
+extern bool mnl_attr_put_u32_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, uint32_t data);
+extern bool mnl_attr_put_u64_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, uint64_t data);
+extern bool mnl_attr_put_str_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, const char *data);
+extern bool mnl_attr_put_strz_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type, const char *data);
+
 /* TLV attribute nesting */
 extern struct nlattr *mnl_attr_nest_start(struct nlmsghdr *nlh, uint16_t type);
+extern struct nlattr *mnl_attr_nest_start_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type);
 extern void mnl_attr_nest_end(struct nlmsghdr *nlh, struct nlattr *start);
 extern void mnl_attr_nest_cancel(struct nlmsghdr *nlh, struct nlattr *start);
 
diff --git a/src/attr.c b/src/attr.c
index 16f390a..8f36791 100644
--- a/src/attr.c
+++ b/src/attr.c
@@ -491,6 +491,180 @@ mnl_attr_nest_start(struct nlmsghdr *nlh, uint16_t type)
 }
 
 /**
+ * mnl_attr_put_check - add an attribute to netlink message
+ * \param nlh pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type that you want to add
+ * \param len netlink attribute payload length
+ * \param data pointer to the data that will be stored by the new attribute
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_check(struct nlmsghdr *nlh, size_t buflen,
+		   uint16_t type, size_t len, const void *data)
+{
+	if (nlh->nlmsg_len + MNL_ATTR_HDRLEN + MNL_ALIGN(len) > buflen)
+		return false;
+	mnl_attr_put(nlh, type, len, data);
+	return true;
+}
+
+/**
+ * mnl_attr_put_u8_check - add 8-bit unsigned int attribute to netlink message
+ * \param nlh pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type
+ * \param len netlink attribute payload size
+ * \param data 8-bit unsigned integer data that is stored by the new attribute
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_u8_check(struct nlmsghdr *nlh, size_t buflen,
+		      uint16_t type, uint8_t data)
+{
+	return mnl_attr_put_check(nlh, buflen, type, sizeof(uint8_t), &data);
+}
+
+/**
+ * mnl_attr_put_u16_check - add 16-bit unsigned int attribute to netlink message
+ * \param nlh pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type
+ * \param data 16-bit unsigned integer data that is stored by the new attribute
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ * This function updates the length field of the Netlink message (nlmsg_len)
+ * by adding the size (header + payload) of the new attribute.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_u16_check(struct nlmsghdr *nlh, size_t buflen,
+		       uint16_t type, uint16_t data)
+{
+	return mnl_attr_put_check(nlh, buflen, type, sizeof(uint16_t), &data);
+}
+
+/**
+ * mnl_attr_put_u32_check - add 32-bit unsigned int attribute to netlink message
+ * \param nlh pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type
+ * \param data 32-bit unsigned integer data that is stored by the new attribute
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ * This function updates the length field of the Netlink message (nlmsg_len)
+ * by adding the size (header + payload) of the new attribute.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_u32_check(struct nlmsghdr *nlh, size_t buflen,
+		       uint16_t type, uint32_t data)
+{
+	return mnl_attr_put_check(nlh, buflen, type, sizeof(uint32_t), &data);
+}
+
+/**
+ * mnl_attr_put_u64_check - add 64-bit unsigned int attribute to netlink message
+ * \param nlh pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type
+ * \param data 64-bit unsigned integer data that is stored by the new attribute
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ * This function updates the length field of the Netlink message (nlmsg_len)
+ * by adding the size (header + payload) of the new attribute.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_u64_check(struct nlmsghdr *nlh, size_t buflen,
+		       uint16_t type, uint64_t data)
+{
+	return mnl_attr_put_check(nlh, buflen, type, sizeof(uint64_t), &data);
+}
+
+/**
+ * mnl_attr_put_str_check - add string attribute to netlink message
+ * \param nlh  pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type
+ * \param data pointer to string data that is stored by the new attribute
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ * This function updates the length field of the Netlink message (nlmsg_len)
+ * by adding the size (header + payload) of the new attribute.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_str_check(struct nlmsghdr *nlh, size_t buflen,
+		       uint16_t type, const char *data)
+{
+	return mnl_attr_put_check(nlh, buflen, type, strlen(data), data);
+}
+
+/**
+ * mnl_attr_put_strz_check - add string attribute to netlink message
+ * \param nlh pointer to the netlink message
+ * \param buflen size of buffer which stores the message
+ * \param type netlink attribute type
+ * \param data pointer to string data that is stored by the new attribute
+ *
+ * This function is similar to mnl_attr_put_str, but it includes the
+ * NUL/zero ('\0') terminator at the end of the string.
+ *
+ * This function first checks that the data can be added to the message
+ * (fits into the buffer) and then updates the length field of the Netlink
+ * message (nlmsg_len) by adding the size (header + payload) of the new
+ * attribute. The function returns true if the attribute could be added
+ * to the message, otherwise false is returned.
+ */
+EXPORT_SYMBOL bool
+mnl_attr_put_strz_check(struct nlmsghdr *nlh, size_t buflen,
+			uint16_t type, const char *data)
+{
+	return mnl_attr_put_check(nlh, buflen, type, strlen(data)+1, data);
+}
+
+/**
+ * mnl_attr_nest_start_check - start an attribute nest
+ * \param buflen size of buffer which stores the message
+ * \param nlh pointer to the netlink message
+ * \param type netlink attribute type
+ *
+ * This function adds the attribute header that identifies the beginning of
+ * an attribute nest. If the nested attribute cannot be added then NULL,
+ * otherwise valid pointer to the beginning of the nest is returned.
+ */
+EXPORT_SYMBOL struct nlattr *
+mnl_attr_nest_start_check(struct nlmsghdr *nlh, size_t buflen, uint16_t type)
+{
+	if (nlh->nlmsg_len + MNL_ATTR_HDRLEN > buflen)
+		return NULL;
+	return mnl_attr_nest_start(nlh, type);
+}
+
+/**
  * mnl_attr_nest_end - end an attribute nest
  * \param nlh pointer to the netlink message
  * \param start pointer to the attribute nest returned by mnl_attr_nest_start()
diff --git a/src/libmnl.map b/src/libmnl.map
index 4bbd06e..01bb924 100644
--- a/src/libmnl.map
+++ b/src/libmnl.map
@@ -11,6 +11,7 @@ global:
   mnl_attr_get_u8;
   mnl_attr_nest_end;
   mnl_attr_nest_start;
+  mnl_attr_nest_start_check;
   mnl_attr_nest_cancel;
   mnl_attr_next;
   mnl_attr_ok;
@@ -23,6 +24,13 @@ global:
   mnl_attr_put_u32;
   mnl_attr_put_u64;
   mnl_attr_put_u8;
+  mnl_attr_put_check;
+  mnl_attr_put_str_check;
+  mnl_attr_put_strz_check;
+  mnl_attr_put_u16_check;
+  mnl_attr_put_u32_check;
+  mnl_attr_put_u64_check;
+  mnl_attr_put_u8_check;
   mnl_attr_type_valid;
   mnl_attr_validate;
   mnl_attr_validate2;