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/*
hostfile.c
Author: Tatu Ylonen <ylo@cs.hut.fi>
Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
All rights reserved
Created: Thu Jun 29 07:10:56 1995 ylo
Functions for manipulating the known hosts files.
*/
#include "includes.h"
RCSID("$Id: hostfile.c,v 1.4 1999/11/17 06:29:08 damien Exp $");
#include "packet.h"
#include "ssh.h"
/* Reads a multiple-precision integer in hex from the buffer, and advances the
pointer. The integer must already be initialized. This function is
permitted to modify the buffer. This leaves *cpp to point just beyond
the last processed (and maybe modified) character. Note that this may
modify the buffer containing the number. */
int
auth_rsa_read_bignum(char **cpp, BIGNUM *value)
{
char *cp = *cpp;
int len, old;
/* Skip any leading whitespace. */
for (; *cp == ' ' || *cp == '\t'; cp++)
;
/* Check that it begins with a hex digit. */
if (*cp < '0' || *cp > '9')
return 0;
/* Save starting position. */
*cpp = cp;
/* Move forward until all hex digits skipped. */
for (; *cp >= '0' && *cp <= '9'; cp++)
;
/* Compute the length of the hex number. */
len = cp - *cpp;
/* Save the old terminating character, and replace it by \0. */
old = *cp;
*cp = 0;
/* Parse the number. */
if (BN_dec2bn(&value, *cpp) == 0)
return 0;
/* Restore old terminating character. */
*cp = old;
/* Move beyond the number and return success. */
*cpp = cp;
return 1;
}
/* Parses an RSA key (number of bits, e, n) from a string. Moves the pointer
over the key. Skips any whitespace at the beginning and at end. */
int
auth_rsa_read_key(char **cpp, unsigned int *bitsp, BIGNUM *e, BIGNUM *n)
{
unsigned int bits;
char *cp;
/* Skip leading whitespace. */
for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
;
/* Get number of bits. */
if (*cp < '0' || *cp > '9')
return 0; /* Bad bit count... */
for (bits = 0; *cp >= '0' && *cp <= '9'; cp++)
bits = 10 * bits + *cp - '0';
/* Get public exponent. */
if (!auth_rsa_read_bignum(&cp, e))
return 0;
/* Get public modulus. */
if (!auth_rsa_read_bignum(&cp, n))
return 0;
/* Skip trailing whitespace. */
for (; *cp == ' ' || *cp == '\t'; cp++)
;
/* Return results. */
*cpp = cp;
*bitsp = bits;
return 1;
}
/* Tries to match the host name (which must be in all lowercase) against the
comma-separated sequence of subpatterns (each possibly preceded by ! to
indicate negation). Returns true if there is a positive match; zero
otherwise. */
int
match_hostname(const char *host, const char *pattern, unsigned int len)
{
char sub[1024];
int negated;
int got_positive;
unsigned int i, subi;
got_positive = 0;
for (i = 0; i < len;)
{
/* Check if the subpattern is negated. */
if (pattern[i] == '!')
{
negated = 1;
i++;
}
else
negated = 0;
/* Extract the subpattern up to a comma or end. Convert the subpattern
to lowercase. */
for (subi = 0;
i < len && subi < sizeof(sub) - 1 && pattern[i] != ',';
subi++, i++)
sub[subi] = isupper(pattern[i]) ? tolower(pattern[i]) : pattern[i];
/* If subpattern too long, return failure (no match). */
if (subi >= sizeof(sub) - 1)
return 0;
/* If the subpattern was terminated by a comma, skip the comma. */
if (i < len && pattern[i] == ',')
i++;
/* Null-terminate the subpattern. */
sub[subi] = '\0';
/* Try to match the subpattern against the host name. */
if (match_pattern(host, sub)) {
if (negated)
return 0; /* Fail if host matches any negated subpattern. */
else
got_positive = 1;
}
}
/* Return success if got a positive match. If there was a negative match,
we have already returned zero and never get here. */
return got_positive;
}
/* Checks whether the given host (which must be in all lowercase) is
already in the list of our known hosts.
Returns HOST_OK if the host is known and has the specified key,
HOST_NEW if the host is not known, and HOST_CHANGED if the host is known
but used to have a different host key. */
HostStatus
check_host_in_hostfile(const char *filename, const char *host,
BIGNUM *e, BIGNUM *n, BIGNUM *ke, BIGNUM *kn)
{
FILE *f;
char line[8192];
int linenum = 0;
unsigned int bits, kbits, hostlen;
char *cp, *cp2;
HostStatus end_return;
/* Open the file containing the list of known hosts. */
f = fopen(filename, "r");
if (!f)
return HOST_NEW;
/* Cache the length of the host name. */
hostlen = strlen(host);
/* Return value when the loop terminates. This is set to HOST_CHANGED if
we have seen a different key for the host and have not found the proper
one. */
end_return = HOST_NEW;
/* size of modulus 'n' */
bits = BN_num_bits(n);
/* Go trough the file. */
while (fgets(line, sizeof(line), f))
{
cp = line;
linenum++;
/* Skip any leading whitespace. */
for (; *cp == ' ' || *cp == '\t'; cp++)
;
/* Ignore comment lines and empty lines. */
if (!*cp || *cp == '#' || *cp == '\n')
continue;
/* Find the end of the host name portion. */
for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
;
/* Check if the host name matches. */
if (!match_hostname(host, cp, (unsigned int)(cp2 - cp)))
continue;
/* Got a match. Skip host name. */
cp = cp2;
/* Extract the key from the line. This will skip any leading
whitespace. Ignore badly formatted lines. */
if (!auth_rsa_read_key(&cp, &kbits, ke, kn))
continue;
if (kbits != BN_num_bits(kn)) {
error("Warning: error in %s, line %d: keysize mismatch for host %s: "
"actual size %d vs. announced %d.",
filename, linenum, host, BN_num_bits(kn), kbits);
error("Warning: replace %d with %d in %s, line %d.",
kbits, BN_num_bits(kn), filename, linenum);
}
/* Check if the current key is the same as the given key. */
if (BN_cmp(ke, e) == 0 && BN_cmp(kn, n) == 0)
{
/* Ok, they match. */
fclose(f);
return HOST_OK;
}
/* They do not match. We will continue to go through the file; however,
we note that we will not return that it is new. */
end_return = HOST_CHANGED;
}
/* Clear variables and close the file. */
fclose(f);
/* Return either HOST_NEW or HOST_CHANGED, depending on whether we saw a
different key for the host. */
return end_return;
}
/* Appends an entry to the host file. Returns false if the entry
could not be appended. */
int
add_host_to_hostfile(const char *filename, const char *host,
BIGNUM *e, BIGNUM *n)
{
FILE *f;
char *buf;
unsigned int bits;
/* Open the file for appending. */
f = fopen(filename, "a");
if (!f)
return 0;
/* size of modulus 'n' */
bits = BN_num_bits(n);
/* Print the host name and key to the file. */
fprintf(f, "%s %u ", host, bits);
buf = BN_bn2dec(e);
if (buf == NULL) {
error("add_host_to_hostfile: BN_bn2dec(e) failed");
fclose(f);
return 0;
}
fprintf(f, "%s ", buf);
free (buf);
buf = BN_bn2dec(n);
if (buf == NULL) {
error("add_host_to_hostfile: BN_bn2dec(n) failed");
fclose(f);
return 0;
}
fprintf(f, "%s\n", buf);
free (buf);
/* Close the file. */
fclose(f);
return 1;
}
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