NAME¶
ipsec_set_policy
,
ipsec_get_policylen
,
ipsec_dump_policy
—
manipulate IPsec policy specification structure from
human-readable policy string
LIBRARY¶
IPsec Policy Control Library (libipsec,
-lipsec)
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 an IPsec policy
specification structure, namely
struct sadb_x_policy
and/or
struct sadb_x_ipsecrequest
from a
human-readable policy specification. The policy specification must be given as
a C string
policy and its length
len.
ipsec_set_policy
() will return a buffer
with the corresponding IPsec policy specification structure. The buffer is
dynamically allocated, and must be
free(3)'d by
the caller.
You can get the length of the generated buffer with
ipsec_get_policylen
() (i.e. for calling
setsockopt(2)).
ipsec_dump_policy
() converts an IPsec policy
structure into human-readable form. Therefore,
ipsec_dump_policy
() can be regarded as the
inverse function to
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
, a single whitespace is assumed.
ipsec_dump_policy
() returns a pointer to a
dynamically allocated string. It is the caller's responsibility to
free(3) it.
policy is formatted as either of the following:
- direction [priority specification]
discard
- direction must be
in
, out
, or
fwd
. direction
specifies in which direction the policy needs to be applied. The
non-standard 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. The 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 (Linux >= 2.6.6). It
takes one of the following formats:
- {priority,prio} offset
- offset is an integer in the range
-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 the SPD defined by
setkey(8).
- direction [priority specification]
bypass
bypass
means to bypass the IPsec processing. (the packet will be transmitted in
clear). This is for privileged sockets.
- 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 strings, which are 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 the IPsec endpoint.
src always means the “sending
node” and dst always means the
“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 omitted.
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 behavior. If
level is omitted, it will be
interpreted as default
.
Note that there are slight differences to the specification of
setkey(8). In the specification of
setkey(8), both
entrust
and bypass
are not
used. Refer to setkey(8) for details.
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 with the policy specification if successful; otherwise a
NULL
pointer is returned.
ipsec_get_policylen
() returns a positive
value (meaning the buffer size) on success, and a negative value on errors.
ipsec_dump_policy
() returns a pointer to a
dynamically allocated region on success, and
NULL
on errors.
SEE ALSO¶
ipsec_strerror(3),
ipsec(4),
setkey(8)
HISTORY¶
The functions first appeared in the WIDE/KAME IPv6 protocol stack kit.