char *
ipsec_set_policy(
char *policy
, int len
)
int
ipsec_get_policylen(
char *buf
)
char *
ipsec_dump_policy(
char *buf
, char *delim
)
)
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)Ap 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:
discard
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:
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.
entrust
entrust
means to consult the SPD defined by
setkey(8).
bypass
bypass
means to bypass the IPsec processing.
(the packet will be transmitted in clear).
This is for privileged sockets.
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:
/
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
)
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.