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New option to manually configure the expected host key(s).

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This option is available from the command line as '-hostkey', and is
also configurable through the GUI. When enabled, it completely
replaces all of the automated host key management: the server's host
key will be checked against the manually configured list, and the
connection will be allowed or disconnected on that basis, and the host
key store in the registry will not be either consulted or updated.

The main aim is to provide a means of automatically running Plink,
PSCP or PSFTP deep inside Windows services where HKEY_CURRENT_USER
isn't available to have stored the right host key in. But it also
permits you to specify a list of multiple host keys, which means a
second use case for the same mechanism will probably be round-robin
DNS names that select one of several servers with different host keys.

Host keys can be specified as the standard MD5 fingerprint or as an
SSH-2 base64 blob, and are canonicalised on input. (The base64 blob is
more unwieldy, especially with Windows command-line length limits, but
provides a means of specifying the _whole_ public key in case you
don't trust MD5. I haven't bothered to provide an analogous mechanism
for SSH-1, on the basis that anyone worrying about MD5 should have
stopped using SSH-1 already!)

[originally from svn r10220]
This commit is contained in:
Simon Tatham
2014-09-09 11:46:24 +00:00
parent f3860ec95e
commit 70ab076d83
11 changed files with 411 additions and 52 deletions
Download Patch File Download Diff File Expand all files Collapse all files

158
ssh.c
View File

@ -3677,6 +3677,59 @@ static void ssh_disconnect(Ssh ssh, char *client_reason, char *wire_reason,
sfree(error);
}
int verify_ssh_manual_host_key(Ssh ssh, const char *fingerprint,
const struct ssh_signkey *ssh2keytype,
void *ssh2keydata)
{
if (!conf_get_str_nthstrkey(ssh->conf, CONF_ssh_manual_hostkeys, 0)) {
return -1; /* no manual keys configured */
}
if (fingerprint) {
/*
* The fingerprint string we've been given will have things
* like 'ssh-rsa 2048' at the front of it. Strip those off and
* narrow down to just the colon-separated hex block at the
* end of the string.
*/
const char *p = strrchr(fingerprint, ' ');
fingerprint = p ? p+1 : fingerprint;
/* Quick sanity checks, including making sure it's in lowercase */
assert(strlen(fingerprint) == 16*3 - 1);
assert(fingerprint[2] == ':');
assert(fingerprint[strspn(fingerprint, "0123456789abcdef:")] == 0);
if (conf_get_str_str_opt(ssh->conf, CONF_ssh_manual_hostkeys,
fingerprint))
return 1; /* success */
}
if (ssh2keydata) {
/*
* Construct the base64-encoded public key blob and see if
* that's listed.
*/
unsigned char *binblob;
char *base64blob;
int binlen, atoms, i;
binblob = ssh2keytype->public_blob(ssh2keydata, &binlen);
atoms = (binlen + 2) / 3;
base64blob = snewn(atoms * 4 + 1, char);
for (i = 0; i < atoms; i++)
base64_encode_atom(binblob + 3*i, binlen - 3*i, base64blob + 4*i);
base64blob[atoms * 4] = '\0';
sfree(binblob);
if (conf_get_str_str_opt(ssh->conf, CONF_ssh_manual_hostkeys,
base64blob)) {
sfree(base64blob);
return 1; /* success */
}
sfree(base64blob);
}
return 0;
}
/*
* Handle the key exchange and user authentication phases.
*/
@ -3800,29 +3853,36 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
rsastr_fmt(keystr, &s->hostkey);
rsa_fingerprint(fingerprint, sizeof(fingerprint), &s->hostkey);
ssh_set_frozen(ssh, 1);
s->dlgret = verify_ssh_host_key(ssh->frontend,
ssh->savedhost, ssh->savedport,
"rsa", keystr, fingerprint,
ssh_dialog_callback, ssh);
sfree(keystr);
if (s->dlgret < 0) {
do {
crReturn(0);
if (pktin) {
bombout(("Unexpected data from server while waiting"
" for user host key response"));
crStop(0);
}
} while (pktin || inlen > 0);
s->dlgret = ssh->user_response;
}
ssh_set_frozen(ssh, 0);
/* First check against manually configured host keys. */
s->dlgret = verify_ssh_manual_host_key(ssh, fingerprint, NULL, NULL);
if (s->dlgret == 0) { /* did not match */
bombout(("Host key did not appear in manually configured list"));
crStop(0);
} else if (s->dlgret < 0) { /* none configured; use standard handling */
ssh_set_frozen(ssh, 1);
s->dlgret = verify_ssh_host_key(ssh->frontend,
ssh->savedhost, ssh->savedport,
"rsa", keystr, fingerprint,
ssh_dialog_callback, ssh);
sfree(keystr);
if (s->dlgret < 0) {
do {
crReturn(0);
if (pktin) {
bombout(("Unexpected data from server while waiting"
" for user host key response"));
crStop(0);
}
} while (pktin || inlen > 0);
s->dlgret = ssh->user_response;
}
ssh_set_frozen(ssh, 0);
if (s->dlgret == 0) {
ssh_disconnect(ssh, "User aborted at host key verification",
NULL, 0, TRUE);
crStop(0);
if (s->dlgret == 0) {
ssh_disconnect(ssh, "User aborted at host key verification",
NULL, 0, TRUE);
crStop(0);
}
}
}
@ -6721,31 +6781,39 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
* checked the signature of the exchange hash.)
*/
s->fingerprint = ssh->hostkey->fingerprint(s->hkey);
ssh_set_frozen(ssh, 1);
s->dlgret = verify_ssh_host_key(ssh->frontend,
ssh->savedhost, ssh->savedport,
ssh->hostkey->keytype, s->keystr,
s->fingerprint,
ssh_dialog_callback, ssh);
if (s->dlgret < 0) {
do {
crReturnV;
if (pktin) {
bombout(("Unexpected data from server while waiting"
" for user host key response"));
crStopV;
}
} while (pktin || inlen > 0);
s->dlgret = ssh->user_response;
}
ssh_set_frozen(ssh, 0);
if (s->dlgret == 0) {
ssh_disconnect(ssh, "User aborted at host key verification", NULL,
0, TRUE);
crStopV;
}
logevent("Host key fingerprint is:");
logevent(s->fingerprint);
/* First check against manually configured host keys. */
s->dlgret = verify_ssh_manual_host_key(ssh, s->fingerprint,
ssh->hostkey, s->hkey);
if (s->dlgret == 0) { /* did not match */
bombout(("Host key did not appear in manually configured list"));
crStopV;
} else if (s->dlgret < 0) { /* none configured; use standard handling */
ssh_set_frozen(ssh, 1);
s->dlgret = verify_ssh_host_key(ssh->frontend,
ssh->savedhost, ssh->savedport,
ssh->hostkey->keytype, s->keystr,
s->fingerprint,
ssh_dialog_callback, ssh);
if (s->dlgret < 0) {
do {
crReturnV;
if (pktin) {
bombout(("Unexpected data from server while waiting"
" for user host key response"));
crStopV;
}
} while (pktin || inlen > 0);
s->dlgret = ssh->user_response;
}
ssh_set_frozen(ssh, 0);
if (s->dlgret == 0) {
ssh_disconnect(ssh, "Aborted at host key verification", NULL,
0, TRUE);
crStopV;
}
}
sfree(s->fingerprint);
/*
* Save this host key, to check against the one presented in