NAME
ipsec ttosa, satot - convert IPsec Security Association IDs to and from
text
ipsec initsaid - initialize an SA ID
SYNOPSIS
#include <freeswan.h>
typedef struct {
ip_address dst;
ipsec_spi_t spi;
int proto;
} ip_said;
const char *ttosa(const char *src, size_t srclen,
ip_said *sa);
size_t satot(const ip_said *sa, int format,
char *dst, size_t dstlen);
void initsaid(const ip_address *addr, ipsec_spi_t spi,
int proto, ip_said *dst);
DESCRIPTION
Ttosa converts an ASCII Security Association (SA) specifier into an
ip_said structure (containing a destination-host address in network
byte order, an SPI number in network byte order, and a protocol code).
Satot does the reverse conversion, back to a text SA specifier.
Initsaid initializes an ip_said from separate items of information.
An SA is specified in text with a mail-like syntax, e.g.
esp.5a7@1.2.3.4. An SA specifier contains a protocol prefix (currently
ah, esp, tun, comp, or int), a single character indicating the address
family (. for IPv4, : for IPv6), an unsigned integer SPI number in
hexadecimal (with no 0x prefix), and an IP address. The IP address can
be any form accepted by ipsec_ttoaddr(3), e.g. dotted-decimal IPv4
address, colon-hex IPv6 address, or DNS name.
As a special case, the SA specifier %passthrough4 or %passthrough6
signifies the special SA used to indicate that packets should be passed
through unaltered. (At present, these are synonyms for tun.0@0.0.0.0
and tun:0@:: respectively, but that is subject to change without
notice.) %passthrough is a historical synonym for %passthrough4.
These forms are known to both ttosa and satot, so the internal
representation is never visible.
Similarly, the SA specifiers %pass, %drop, %reject, %hold, %trap, and
%trapsubnet signify special ‘‘magic’’ SAs used to indicate that packets
should be passed, dropped, rejected (dropped with ICMP notification),
held, and trapped (sent up to ipsec_pluto(8), with either of two forms
of %hold automatically installed) respectively. These forms too are
known to both routines, so the internal representation of the magic SAs
should never be visible.
The <freeswan.h> header file supplies the ip_said structure, as well as
a data type ipsec_spi_t which is an unsigned 32-bit integer. (There is
no consistency between kernel and user on what such a type is called,
hence the header hides the differences.)
The protocol code uses the same numbers that IP does. For user
convenience, given the difficulty in acquiring the exact set of
protocol names used by the kernel, <freeswan.h> defines the names
SA_ESP, SA_AH, SA_IPIP, and SA_COMP to have the same values as the
kernel names IPPROTO_ESP, IPPROTO_AH, IPPROTO_IPIP, and IPPROTO_COMP.
<freeswan.h> also defines SA_INT to have the value 61 (reserved by IANA
for ‘‘any host internal protocol’’) and SPI_PASS, SPI_DROP, SPI_REJECT,
SPI_HOLD, and SPI_TRAP to have the values 256-260 (in host byte order)
respectively. These are used in constructing the magic SAs (which
always have address 0.0.0.0).
If satot encounters an unknown protocol code, e.g. 77, it yields output
using a prefix showing the code numerically, e.g. ‘‘unk77’’. This form
is not recognized by ttosa.
The srclen parameter of ttosa specifies the length of the string
pointed to by src; it is an error for there to be anything else (e.g.,
a terminating NUL) within that length. As a convenience for cases
where an entire NUL-terminated string is to be converted, a srclen
value of 0 is taken to mean strlen(src).
The dstlen parameter of satot specifies the size of the dst parameter;
under no circumstances are more than dstlen bytes written to dst. A
result which will not fit is truncated. Dstlen can be zero, in which
case dst need not be valid and no result is written, but the return
value is unaffected; in all other cases, the (possibly truncated)
result is NUL-terminated. The <freeswan.h> header file defines a
constant, SATOT_BUF, which is the size of a buffer just large enough
for worst-case results.
The format parameter of satot specifies what format is to be used for
the conversion. The value 0 (not the ASCII character ’0’, but a zero
value) specifies a reasonable default (currently lowercase protocol
prefix, lowercase hexadecimal SPI, dotted-decimal or colon-hex
address). The value ’f’ is similar except that the SPI is padded with
0s to a fixed 32-bit width, to ease aligning displayed tables.
Ttosa returns NULL for success and a pointer to a string-literal error
message for failure; see DIAGNOSTICS. Satot returns 0 for a failure,
and otherwise always returns the size of buffer which would be needed
to accommodate the full conversion result, including terminating NUL;
it is the caller’s responsibility to check this against the size of the
provided buffer to determine whether truncation has occurred.
There is also, temporarily, support for some obsolete forms of SA
specifier which lack the address-family indicator.
SEE ALSO
ipsec_ttoul(3), ipsec_ttoaddr(3), ipsec_samesaid(3), inet(3)
DIAGNOSTICS
Fatal errors in ttosa are: empty input; input too small to be a legal
SA specifier; no @ in input; unknown protocol prefix; conversion error
in ttoul or ttoaddr.
Fatal errors in satot are: unknown format.
HISTORY
Written for the FreeS/WAN project by Henry Spencer.
BUGS
The restriction of text-to-binary error reports to literal strings (so
that callers don’t need to worry about freeing them or copying them)
does limit the precision of error reporting.
The text-to-binary error-reporting convention lends itself to slightly
obscure code, because many readers will not think of NULL as signifying
success. A good way to make it clearer is to write something like:
const char *error;
error = ttosa( /* ... */ );
if (error != NULL) {
/* something went wrong */
26 Nov 2001