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Diffstat (limited to 'package/libnl-tiny/src/attr.c')
| -rw-r--r-- | package/libnl-tiny/src/attr.c | 668 |
1 files changed, 668 insertions, 0 deletions
diff --git a/package/libnl-tiny/src/attr.c b/package/libnl-tiny/src/attr.c new file mode 100644 index 0000000..e0f5061 --- /dev/null +++ b/package/libnl-tiny/src/attr.c @@ -0,0 +1,668 @@ +/* + * 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; +} + + + +/** @} */ |