IPSEC_SET_POLICY(3)

NAME
ipsec_set_policy, ipsec_get_policylen, ipsec_dump_policy - manipulate IPsec policy specification structure from readable string

LIBRARY
libipsec

SYNOPSIS
#include <netinet6/ipsec.h>
char *
ipsec_set_policy(char *policy, int len);
int
ipsec_get_policylen(char *buf);
char *
ipsec_dump_policy(char *buf, char *delim);

DESCRIPTION
ipsec_set_policy() generates IPsec policy specification structure, namely struct sadb_x_policy and/or struct sadb_x_ipsecrequest from human-readable policy specification. policy specification must be given as C string policy and length len of policy. ipsec_set_policy() will return the buffer of IPsec policy specification structure. The buffer is dynamically allocated, and must be freed by the caller by calling free(3).

You may want the length of the generated buffer such when calling setsockopt(2). ipsec_get_policylen() will return the length.

ipsec_dump_policy() converts IPsec policy structure into readable form. Therefore, ipsec_dump_policy() can be regarded as inverse conversion of ipsec_set_policy(). buf points to an IPsec policy structure, struct sadb_x_policy. delim is a delimiter string, which is usually a blank character. If you set delim to NULL, single whitespace is assumed. ipsec_dump_policy() returns pointer to dynamically allocated string. It is caller's responsibility to reclaim the region, by using free(3).

policy is formatted as either of the following:

direction [priority specification] discard
    direction must be in , out or fwd. direction specifies which direction the policy needs to be applied. Nonstandard direction fwd is substituted with in on platforms which do not support forward policies.

    priority specification is used to control the placement of the policy within the SPD. Policy position is determined by a signed integer where higher priorities indicate the policy is placed closer to the beginning of the list and lower priorities indicate the policy is placed closer to the end of the list. Policies with equal priorities are added at the end of the group of such policies.

    Priority can only be specified when libipsec has been compiled against kernel headers that support policy priorities (>= 2.6.6). It takes one of the following formats:

        {priority,prio} offset offset is an integer in ranges -2147483647 .. 214783648.

        {priority,prio} base {+,-} offset base is either low (-1073741824), def (0), or high (1073741824)

        offset is an unsigned integer. It can be up to 1073741824 for positive offsets, and up to 1073741823 for negative offsets.

    The interpretation of policy priority in these functions and the kernel DOES differ. The relationship between the two can be described as p(kernel) = 0x80000000 - p(func)

    With discard policy, packets will be dropped if they match the policy.

direction [priority specification] entrust
    entrust means to consult to SPD defined by setkey(8).

direction [priority specification] bypass
    bypass means to be bypassed the IPsec processing. (packet will be transmitted in clear). This is for privileged socket.

    direction [priority specification] ipsec request ... ipsec means that the matching packets are subject to IPsec processing. ipsec can be followed by one or more request string, which is formatted as below:

        protocol / mode / src - dst [/level] protocol is either ah, esp or ipcomp.

        mode is either transport or tunnel.

        src and dst specifies IPsec endpoint. src always means “sending node” and dst always means “receiving node”. Therefore, when direction is in, dst is this node and src is the other node (peer). If mode is transport, Both src and dst can be omited.

        level must be set to one of the following: default, use, require or unique. default means that the kernel should consult the system default policy defined by sysctl(8), such as net.inet.ipsec.esp_trans_deflev. See ipsec(4) regarding the system default. use means that a relevant SA can be used when available, since the kernel may perform IPsec operation against packets when possible. In this case, packets can be transmitted in clear (when SA is not available), or encrypted (when SA is available). require means that a relevant SA is required, since the kernel must perform IPsec operation against packets. unique is the same as require, but adds the restriction that the SA for outbound traffic is used only for this policy. You may need the identifier in order to relate the policy and the SA when you define the SA by manual keying. You can put the decimal number as the identifier after unique like unique: number. number must be between 1 and 32767 . If the request string is kept unambiguous, level and slash prior to level can be omitted. However, it is encouraged to specify them explicitly to avoid unintended behaviors. If level is omitted, it will be interpreted as default.

    Note that there is a bit difference of specification from setkey(8). In specification by setkey(8), both entrust and bypass are not used. Refer to setkey(8) for detail.

    Here are several examples (long lines are wrapped for readability):

        in discard
        out ipsec esp/transport//require
        in ipsec ah/transport//require
        out ipsec esp/tunnel/10.1.1.2-10.1.1.1/use
        in ipsec ipcomp/transport//use
                esp/transport//use

RETURN VALUES
ipsec_set_policy() returns a pointer to the allocated buffer of policy specification if successful; otherwise a NULL pointer is returned. ipsec_get_policylen() returns with positive value (meaning the buffer size) on success, and negative value on errors. ipsec_dump_policy() returns a pointer to dynamically allocated region on success, and NULL on errors.

SEE ALSO
ipsec_strerror(3), ipsec(4), setkey(8)

HISTORY
The functions first appeared in WIDE/KAME IPv6 protocol stack kit.