+++ /dev/null
-/*
- * lib/attr.c Netlink Attributes
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation version 2.1
- * of the License.
- *
- * Copyright (c) 2003-2008 Thomas Graf <tgraf@suug.ch>
- */
-
-#include <netlink-local.h>
-#include <netlink/netlink.h>
-#include <netlink/utils.h>
-#include <netlink/addr.h>
-#include <netlink/attr.h>
-#include <netlink/msg.h>
-#include <linux/socket.h>
-
-/**
- * @ingroup msg
- * @defgroup attr Attributes
- * Netlink Attributes Construction/Parsing Interface
- *
- * \section attr_sec Netlink Attributes
- * Netlink attributes allow for data chunks of arbitary length to be
- * attached to a netlink message. Each attribute is encoded with a
- * type and length field, both 16 bits, stored in the attribute header
- * preceding the attribute data. The main advantage of using attributes
- * over packing everything into the family header is that the interface
- * stays extendable as new attributes can supersede old attributes while
- * remaining backwards compatible. Also attributes can be defined optional
- * thus avoiding the transmission of unnecessary empty data blocks.
- * Special nested attributes allow for more complex data structures to
- * be transmitted, e.g. trees, lists, etc.
- *
- * While not required, netlink attributes typically follow the family
- * header of a netlink message and must be properly aligned to NLA_ALIGNTO:
- * @code
- * +----------------+- - -+---------------+- - -+------------+- - -+
- * | Netlink Header | Pad | Family Header | Pad | Attributes | Pad |
- * +----------------+- - -+---------------+- - -+------------+- - -+
- * @endcode
- *
- * The actual attributes are chained together each separately aligned to
- * NLA_ALIGNTO. The position of an attribute is defined based on the
- * length field of the preceding attributes:
- * @code
- * +-------------+- - -+-------------+- - -+------
- * | Attribute 1 | Pad | Attribute 2 | Pad | ...
- * +-------------+- - -+-------------+- - -+------
- * nla_next(attr1)------^
- * @endcode
- *
- * The attribute itself consists of the attribute header followed by
- * the actual payload also aligned to NLA_ALIGNTO. The function nla_data()
- * returns a pointer to the start of the payload while nla_len() returns
- * the length of the payload in bytes.
- *
- * \b Note: Be aware, NLA_ALIGNTO equals to 4 bytes, therefore it is not
- * safe to dereference any 64 bit data types directly.
- *
- * @code
- * <----------- nla_total_size(payload) ----------->
- * <-------- nla_attr_size(payload) --------->
- * +------------------+- - -+- - - - - - - - - +- - -+
- * | Attribute Header | Pad | Payload | Pad |
- * +------------------+- - -+- - - - - - - - - +- - -+
- * nla_data(nla)-------------^
- * <- nla_len(nla) ->
- * @endcode
- *
- * @subsection attr_datatypes Attribute Data Types
- * A number of basic data types are supported to simplify access and
- * validation of netlink attributes. This data type information is
- * not encoded in the attribute, both the kernel and userspace part
- * are required to share this information on their own.
- *
- * One of the major advantages of these basic types is the automatic
- * validation of each attribute based on an attribute policy. The
- * validation covers most of the checks required to safely use
- * attributes and thus keeps the individual sanity check to a minimum.
- *
- * Never access attribute payload without ensuring basic validation
- * first, attributes may:
- * - not be present even though required
- * - contain less actual payload than expected
- * - fake a attribute length which exceeds the end of the message
- * - contain unterminated character strings
- *
- * Policies are defined as array of the struct nla_policy. The array is
- * indexed with the attribute type, therefore the array must be sized
- * accordingly.
- * @code
- * static struct nla_policy my_policy[ATTR_MAX+1] = {
- * [ATTR_FOO] = { .type = ..., .minlen = ..., .maxlen = ... },
- * };
- *
- * err = nla_validate(attrs, attrlen, ATTR_MAX, &my_policy);
- * @endcode
- *
- * Some basic validations are performed on every attribute, regardless of type.
- * - If the attribute type exceeds the maximum attribute type specified or
- * the attribute type is lesser-or-equal than zero, the attribute will
- * be silently ignored.
- * - If the payload length falls below the \a minlen value the attribute
- * will be rejected.
- * - If \a maxlen is non-zero and the payload length exceeds the \a maxlen
- * value the attribute will be rejected.
- *
- *
- * @par Unspecific Attribute (NLA_UNSPEC)
- * This is the standard type if no type is specified. It is used for
- * binary data of arbitary length. Typically this attribute carries
- * a binary structure or a stream of bytes.
- * @par
- * @code
- * // In this example, we will assume a binary structure requires to
- * // be transmitted. The definition of the structure will typically
- * // go into a header file available to both the kernel and userspace
- * // side.
- * //
- * // Note: Be careful when putting 64 bit data types into a structure.
- * // The attribute payload is only aligned to 4 bytes, dereferencing
- * // the member may fail.
- * struct my_struct {
- * int a;
- * int b;
- * };
- *
- * // The validation function will not enforce an exact length match to
- * // allow structures to grow as required. Note: While it is allowed
- * // to add members to the end of the structure, changing the order or
- * // inserting members in the middle of the structure will break your
- * // binary interface.
- * static struct nla_policy my_policy[ATTR_MAX+1] = {
- * [ATTR_MY_STRICT] = { .type = NLA_UNSPEC,
- * .minlen = sizeof(struct my_struct) },
- *
- * // The binary structure is appened to the message using nla_put()
- * struct my_struct foo = { .a = 1, .b = 2 };
- * nla_put(msg, ATTR_MY_STRUCT, sizeof(foo), &foo);
- *
- * // On the receiving side, a pointer to the structure pointing inside
- * // the message payload is returned by nla_get().
- * if (attrs[ATTR_MY_STRUCT])
- * struct my_struct *foo = nla_get(attrs[ATTR_MY_STRUCT]);
- * @endcode
- *
- * @par Integers (NLA_U8, NLA_U16, NLA_U32, NLA_U64)
- * Integers come in different sizes from 8 bit to 64 bit. However, since the
- * payload length is aligned to 4 bytes, integers smaller than 32 bit are
- * only useful to enforce the maximum range of values.
- * @par
- * \b Note: There is no difference made between signed and unsigned integers.
- * The validation only enforces the minimal payload length required to store
- * an integer of specified type.
- * @par
- * @code
- * // Even though possible, it does not make sense to specify .minlen or
- * // .maxlen for integer types. The data types implies the corresponding
- * // minimal payload length.
- * static struct nla_policy my_policy[ATTR_MAX+1] = {
- * [ATTR_FOO] = { .type = NLA_U32 },
- *
- * // Numeric values can be appended directly using the respective
- * // nla_put_uxxx() function
- * nla_put_u32(msg, ATTR_FOO, 123);
- *
- * // Same for the receiving side.
- * if (attrs[ATTR_FOO])
- * uint32_t foo = nla_get_u32(attrs[ATTR_FOO]);
- * @endcode
- *
- * @par Character string (NLA_STRING)
- * This data type represents a NUL terminated character string of variable
- * length. For binary data streams the type NLA_UNSPEC is recommended.
- * @par
- * @code
- * // Enforce a NUL terminated character string of at most 4 characters
- * // including the NUL termination.
- * static struct nla_policy my_policy[ATTR_MAX+1] = {
- * [ATTR_BAR] = { .type = NLA_STRING, maxlen = 4 },
- *
- * // nla_put_string() creates a string attribute of the necessary length
- * // and appends it to the message including the NUL termination.
- * nla_put_string(msg, ATTR_BAR, "some text");
- *
- * // It is safe to use the returned character string directly if the
- * // attribute has been validated as the validation enforces the proper
- * // termination of the string.
- * if (attrs[ATTR_BAR])
- * char *text = nla_get_string(attrs[ATTR_BAR]);
- * @endcode
- *
- * @par Flag (NLA_FLAG)
- * This attribute type may be used to indicate the presence of a flag. The
- * attribute is only valid if the payload length is zero. The presence of
- * the attribute header indicates the presence of the flag.
- * @par
- * @code
- * // This attribute type is special as .minlen and .maxlen have no effect.
- * static struct nla_policy my_policy[ATTR_MAX+1] = {
- * [ATTR_FLAG] = { .type = NLA_FLAG },
- *
- * // nla_put_flag() appends a zero sized attribute to the message.
- * nla_put_flag(msg, ATTR_FLAG);
- *
- * // There is no need for a receival function, the presence is the value.
- * if (attrs[ATTR_FLAG])
- * // flag is present
- * @endcode
- *
- * @par Micro Seconds (NLA_MSECS)
- *
- * @par Nested Attribute (NLA_NESTED)
- * Attributes can be nested and put into a container to create groups, lists
- * or to construct trees of attributes. Nested attributes are often used to
- * pass attributes to a subsystem where the top layer has no knowledge of the
- * configuration possibilities of each subsystem.
- * @par
- * \b Note: When validating the attributes using nlmsg_validate() or
- * nlmsg_parse() it will only affect the top level attributes. Each
- * level of nested attributes must be validated seperately using
- * nla_parse_nested() or nla_validate().
- * @par
- * @code
- * // The minimal length policy may be used to enforce the presence of at
- * // least one attribute.
- * static struct nla_policy my_policy[ATTR_MAX+1] = {
- * [ATTR_OPTS] = { .type = NLA_NESTED, minlen = NLA_HDRLEN },
- *
- * // Nested attributes are constructed by enclosing the attributes
- * // to be nested with calls to nla_nest_start() respetively nla_nest_end().
- * struct nlattr *opts = nla_nest_start(msg, ATTR_OPTS);
- * nla_put_u32(msg, ATTR_FOO, 123);
- * nla_put_string(msg, ATTR_BAR, "some text");
- * nla_nest_end(msg, opts);
- *
- * // Various methods exist to parse nested attributes, the easiest being
- * // nla_parse_nested() which also allows validation in the same step.
- * if (attrs[ATTR_OPTS]) {
- * struct nlattr *nested[ATTR_MAX+1];
- *
- * nla_parse_nested(nested, ATTR_MAX, attrs[ATTR_OPTS], &policy);
- *
- * if (nested[ATTR_FOO])
- * uint32_t foo = nla_get_u32(nested[ATTR_FOO]);
- * }
- * @endcode
- *
- * @subsection attr_exceptions Exception Based Attribute Construction
- * Often a large number of attributes are added to a message in a single
- * function. In order to simplify error handling, a second set of
- * construction functions exist which jump to a error label when they
- * fail instead of returning an error code. This second set consists
- * of macros which are named after their error code based counterpart
- * except that the name is written all uppercase.
- *
- * All of the macros jump to the target \c nla_put_failure if they fail.
- * @code
- * void my_func(struct nl_msg *msg)
- * {
- * NLA_PUT_U32(msg, ATTR_FOO, 10);
- * NLA_PUT_STRING(msg, ATTR_BAR, "bar");
- *
- * return 0;
- *
- * nla_put_failure:
- * return -NLE_NOMEM;
- * }
- * @endcode
- *
- * @subsection attr_examples Examples
- * @par Example 1.1 Constructing a netlink message with attributes.
- * @code
- * struct nl_msg *build_msg(int ifindex, struct nl_addr *lladdr, int mtu)
- * {
- * struct nl_msg *msg;
- * struct nlattr *info, *vlan;
- * struct ifinfomsg ifi = {
- * .ifi_family = AF_INET,
- * .ifi_index = ifindex,
- * };
- *
- * // Allocate a new netlink message, type=RTM_SETLINK, flags=NLM_F_ECHO
- * if (!(msg = nlmsg_alloc_simple(RTM_SETLINK, NLM_F_ECHO)))
- * return NULL;
- *
- * // Append the family specific header (struct ifinfomsg)
- * if (nlmsg_append(msg, &ifi, sizeof(ifi), NLMSG_ALIGNTO) < 0)
- * goto nla_put_failure
- *
- * // Append a 32 bit integer attribute to carry the MTU
- * NLA_PUT_U32(msg, IFLA_MTU, mtu);
- *
- * // Append a unspecific attribute to carry the link layer address
- * NLA_PUT_ADDR(msg, IFLA_ADDRESS, lladdr);
- *
- * // Append a container for nested attributes to carry link information
- * if (!(info = nla_nest_start(msg, IFLA_LINKINFO)))
- * goto nla_put_failure;
- *
- * // Put a string attribute into the container
- * NLA_PUT_STRING(msg, IFLA_INFO_KIND, "vlan");
- *
- * // Append another container inside the open container to carry
- * // vlan specific attributes
- * if (!(vlan = nla_nest_start(msg, IFLA_INFO_DATA)))
- * goto nla_put_failure;
- *
- * // add vlan specific info attributes here...
- *
- * // Finish nesting the vlan attributes and close the second container.
- * nla_nest_end(msg, vlan);
- *
- * // Finish nesting the link info attribute and close the first container.
- * nla_nest_end(msg, info);
- *
- * return msg;
- *
- * // If any of the construction macros fails, we end up here.
- * nla_put_failure:
- * nlmsg_free(msg);
- * return NULL;
- * }
- * @endcode
- *
- * @par Example 2.1 Parsing a netlink message with attributes.
- * @code
- * int parse_message(struct nl_msg *msg)
- * {
- * // The policy defines two attributes: a 32 bit integer and a container
- * // for nested attributes.
- * struct nla_policy attr_policy[ATTR_MAX+1] = {
- * [ATTR_FOO] = { .type = NLA_U32 },
- * [ATTR_BAR] = { .type = NLA_NESTED },
- * };
- * struct nlattr *attrs[ATTR_MAX+1];
- * int err;
- *
- * // The nlmsg_parse() function will make sure that the message contains
- * // enough payload to hold the header (struct my_hdr), validates any
- * // attributes attached to the messages and stores a pointer to each
- * // attribute in the attrs[] array accessable by attribute type.
- * if ((err = nlmsg_parse(nlmsg_hdr(msg), sizeof(struct my_hdr), attrs,
- * ATTR_MAX, attr_policy)) < 0)
- * goto errout;
- *
- * if (attrs[ATTR_FOO]) {
- * // It is safe to directly access the attribute payload without
- * // any further checks since nlmsg_parse() enforced the policy.
- * uint32_t foo = nla_get_u32(attrs[ATTR_FOO]);
- * }
- *
- * if (attrs[ATTR_BAR]) {
- * struct nlattr *nested[NESTED_MAX+1];
- *
- * // Attributes nested in a container can be parsed the same way
- * // as top level attributes.
- * if ((err = nla_parse_nested(nested, NESTED_MAX, attrs[ATTR_BAR],
- * nested_policy)) < 0)
- * goto errout;
- *
- * // Process nested attributes here.
- * }
- *
- * err = 0;
- * errout:
- * return err;
- * }
- * @endcode
- *
- * @{
- */
-
-/**
- * @name Attribute Size Calculation
- * @{
- */
-
-/** @} */
-
-/**
- * @name Parsing Attributes
- * @{
- */
-
-/**
- * Check if the attribute header and payload can be accessed safely.
- * @arg nla Attribute of any kind.
- * @arg remaining Number of bytes remaining in attribute stream.
- *
- * Verifies that the header and payload do not exceed the number of
- * bytes left in the attribute stream. This function must be called
- * before access the attribute header or payload when iterating over
- * the attribute stream using nla_next().
- *
- * @return True if the attribute can be accessed safely, false otherwise.
- */
-int nla_ok(const struct nlattr *nla, int remaining)
-{
- return remaining >= sizeof(*nla) &&
- nla->nla_len >= sizeof(*nla) &&
- nla->nla_len <= remaining;
-}
-
-/**
- * Return next attribute in a stream of attributes.
- * @arg nla Attribute of any kind.
- * @arg remaining Variable to count remaining bytes in stream.
- *
- * Calculates the offset to the next attribute based on the attribute
- * given. The attribute provided is assumed to be accessible, the
- * caller is responsible to use nla_ok() beforehand. The offset (length
- * of specified attribute including padding) is then subtracted from
- * the remaining bytes variable and a pointer to the next attribute is
- * returned.
- *
- * nla_next() can be called as long as remainig is >0.
- *
- * @return Pointer to next attribute.
- */
-struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
-{
- int totlen = NLA_ALIGN(nla->nla_len);
-
- *remaining -= totlen;
- return (struct nlattr *) ((char *) nla + totlen);
-}
-
-static uint16_t nla_attr_minlen[NLA_TYPE_MAX+1] = {
- [NLA_U8] = sizeof(uint8_t),
- [NLA_U16] = sizeof(uint16_t),
- [NLA_U32] = sizeof(uint32_t),
- [NLA_U64] = sizeof(uint64_t),
- [NLA_STRING] = 1,
-};
-
-static int validate_nla(struct nlattr *nla, int maxtype,
- struct nla_policy *policy)
-{
- struct nla_policy *pt;
- int minlen = 0, type = nla_type(nla);
-
- if (type <= 0 || type > maxtype)
- return 0;
-
- pt = &policy[type];
-
- if (pt->type > NLA_TYPE_MAX)
- BUG();
-
- 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 -NLE_RANGE;
-
- if (nla_len(nla) < minlen)
- return -NLE_RANGE;
-
- if (pt->maxlen && nla_len(nla) > pt->maxlen)
- return -NLE_RANGE;
-
- if (pt->type == NLA_STRING) {
- char *data = nla_data(nla);
- if (data[nla_len(nla) - 1] != '\0')
- return -NLE_INVAL;
- }
-
- return 0;
-}
-
-
-/**
- * Create attribute index based on a stream of attributes.
- * @arg tb Index array to be filled (maxtype+1 elements).
- * @arg maxtype Maximum attribute type expected and accepted.
- * @arg head Head of attribute stream.
- * @arg len Length of attribute stream.
- * @arg policy Attribute validation policy.
- *
- * Iterates over the stream of attributes and stores a pointer to each
- * attribute in the index array using the attribute type as index to
- * the array. Attribute with a type greater than the maximum type
- * specified will be silently ignored in order to maintain backwards
- * compatibility. If \a policy is not NULL, the attribute will be
- * validated using the specified policy.
- *
- * @see nla_validate
- * @return 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) {
- int type = nla_type(nla);
-
- if (type == 0) {
- fprintf(stderr, "Illegal nla->nla_type == 0\n");
- continue;
- }
-
- if (type <= maxtype) {
- if (policy) {
- err = validate_nla(nla, maxtype, policy);
- if (err < 0)
- goto errout;
- }
-
- tb[type] = nla;
- }
- }
-
- if (rem > 0)
- fprintf(stderr, "netlink: %d bytes leftover after parsing "
- "attributes.\n", rem);
-
- err = 0;
-errout:
- return err;
-}
-
-/**
- * Validate a stream of attributes.
- * @arg head Head of attributes stream.
- * @arg len Length of attributes stream.
- * @arg maxtype Maximum attribute type expected and accepted.
- * @arg policy Validation policy.
- *
- * Iterates over the stream of attributes and validates each attribute
- * one by one using the specified policy. Attributes with a type greater
- * than the maximum type specified will be silently ignored in order to
- * maintain backwards compatibility.
- *
- * See \ref attr_datatypes for more details on what kind of validation
- * checks are performed on each attribute data type.
- *
- * @return 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;
-}
-
-/**
- * Find a single attribute in a stream of attributes.
- * @arg head Head of attributes stream.
- * @arg len Length of attributes stream.
- * @arg attrtype Attribute type to look for.
- *
- * Iterates over the stream of attributes and compares each type with
- * the type specified. Returns the first attribute which matches the
- * type.
- *
- * @return Pointer to attribute found or NULL.
- */
-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_type(nla) == attrtype)
- return nla;
-
- return NULL;
-}
-
-/** @} */
-
-/**
- * @name Unspecific Attribute
- * @{
- */
-
-/**
- * Reserve space for a attribute.
- * @arg msg Netlink Message.
- * @arg attrtype Attribute Type.
- * @arg attrlen Length of payload.
- *
- * Reserves room for a attribute in the specified netlink message and
- * fills in the attribute header (type, length). Returns NULL if there
- * is unsuficient space for the attribute.
- *
- * Any padding between payload and the start of the next attribute is
- * zeroed out.
- *
- * @return Pointer to start of attribute or NULL on failure.
- */
-struct nlattr *nla_reserve(struct nl_msg *msg, int attrtype, int attrlen)
-{
- struct nlattr *nla;
- int tlen;
-
- tlen = NLMSG_ALIGN(msg->nm_nlh->nlmsg_len) + nla_total_size(attrlen);
-
- if ((tlen + msg->nm_nlh->nlmsg_len) > msg->nm_size)
- return NULL;
-
- nla = (struct nlattr *) nlmsg_tail(msg->nm_nlh);
- nla->nla_type = attrtype;
- nla->nla_len = nla_attr_size(attrlen);
-
- memset((unsigned char *) nla + nla->nla_len, 0, nla_padlen(attrlen));
- msg->nm_nlh->nlmsg_len = tlen;
-
- NL_DBG(2, "msg %p: Reserved %d bytes at offset +%td for attr %d "
- "nlmsg_len=%d\n", msg, attrlen,
- (void *) nla - nlmsg_data(msg->nm_nlh),
- attrtype, msg->nm_nlh->nlmsg_len);
-
- return nla;
-}
-
-/**
- * Add a unspecific attribute to netlink message.
- * @arg msg Netlink message.
- * @arg attrtype Attribute type.
- * @arg datalen Length of data to be used as payload.
- * @arg data Pointer to data to be used as attribute payload.
- *
- * Reserves room for a unspecific attribute and copies the provided data
- * into the message as payload of the attribute. Returns an error if there
- * is insufficient space for the attribute.
- *
- * @see nla_reserve
- * @return 0 on success or a negative error code.
- */
-int nla_put(struct nl_msg *msg, int attrtype, int datalen, const void *data)
-{
- struct nlattr *nla;
-
- nla = nla_reserve(msg, attrtype, datalen);
- if (!nla)
- return -NLE_NOMEM;
-
- memcpy(nla_data(nla), data, datalen);
- NL_DBG(2, "msg %p: Wrote %d bytes at offset +%td for attr %d\n",
- msg, datalen, (void *) nla - nlmsg_data(msg->nm_nlh), attrtype);
-
- return 0;
-}
-
-
-
-/** @} */
projects / openwrt / svn-archive / archive.git / blobdiff