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upstream: when prompting the user to accept a new hostkey, display 

any other host names/addresses already associated with the key. E.g.

> The authenticity of host 'test (10.0.0.1)' can't be established.
> ECDSA key fingerprint is SHA256:milU4MODXm8iJQI18wlsbPG7Yup+34fuNNmV08qDnax.
> This host key is known by the following other names/addresses:
>     ~/.ssh/known_hosts:1: host.example.org,10.0.0.1
>     ~/.ssh/known_hosts:2: [hashed name]
>     ~/.ssh/known_hosts:3: [hashed name]
>     ~/.ssh/known_hosts:4: host
>     ~/.ssh/known_hosts:5: [host]:2222
> Are you sure you want to continue connecting (yes/no/[fingerprint])?

feedback and ok markus@

OpenBSD-Commit-ID: f6f58a77b49f1368b5883b3a1f776447cfcc7ef4
This commit is contained in:
djm@openbsd.org 2020-11-12 22:56:00 +00:00 committed by Darren Tucker
parent 819b44e8b9
commit d5d05cdb3d
1 changed files with 191 additions and 28 deletions
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219
sshconnect.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: sshconnect.c,v 1.341 2020/10/18 11:32:02 djm Exp $ */
/* $OpenBSD: sshconnect.c,v 1.342 2020/11/12 22:56:00 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -700,6 +700,166 @@ path_in_hostfiles(const char *path, char **hostfiles, u_int num_hostfiles)
return 0;
}
struct find_by_key_ctx {
const char *host, *ip;
const struct sshkey *key;
char **names;
u_int nnames;
};
/* Try to replace home directory prefix (per $HOME) with a ~/ sequence */
static char *
try_tilde_unexpand(const char *path)
{
char *home, *ret = NULL;
size_t l;
if (*path != '/')
return xstrdup(path);
if ((home = getenv("HOME")) == NULL || (l = strlen(home)) == 0)
return xstrdup(path);
if (strncmp(path, home, l) != 0)
return xstrdup(path);
/*
* ensure we have matched on a path boundary: either the $HOME that
* we just compared ends with a '/' or the next character of the path
* must be a '/'.
*/
if (home[l - 1] != '/' && path[l] != '/')
return xstrdup(path);
if (path[l] == '/')
l++;
xasprintf(&ret, "~/%s", path + l);
return ret;
}
static int
hostkeys_find_by_key_cb(struct hostkey_foreach_line *l, void *_ctx)
{
struct find_by_key_ctx *ctx = (struct find_by_key_ctx *)_ctx;
char *path;
/* we are looking for keys with names that *do not* match */
if ((l->match & HKF_MATCH_HOST) != 0)
return 0;
/* not interested in marker lines */
if (l->marker != MRK_NONE)
return 0;
/* we are only interested in exact key matches */
if (l->key == NULL || !sshkey_equal(ctx->key, l->key))
return 0;
path = try_tilde_unexpand(l->path);
debug_f("found matching key in %s:%lu", path, l->linenum);
ctx->names = xrecallocarray(ctx->names,
ctx->nnames, ctx->nnames + 1, sizeof(*ctx->names));
xasprintf(&ctx->names[ctx->nnames], "%s:%lu: %s", path, l->linenum,
strncmp(l->hosts, HASH_MAGIC, strlen(HASH_MAGIC)) == 0 ?
"[hashed name]" : l->hosts);
ctx->nnames++;
free(path);
return 0;
}
static int
hostkeys_find_by_key_hostfile(const char *file, const char *which,
struct find_by_key_ctx *ctx)
{
int r;
debug3_f("trying %s hostfile \"%s\"", which, file);
if ((r = hostkeys_foreach(file, hostkeys_find_by_key_cb, ctx,
ctx->host, ctx->ip, HKF_WANT_PARSE_KEY)) != 0) {
if (r == SSH_ERR_SYSTEM_ERROR && errno == ENOENT) {
debug_f("hostkeys file %s does not exist", file);
return 0;
}
error_fr(r, "hostkeys_foreach failed for %s", file);
return r;
}
return 0;
}
/*
* Find 'key' in known hosts file(s) that do not match host/ip.
* Used to display also-known-as information for previously-unseen hostkeys.
*/
static void
hostkeys_find_by_key(const char *host, const char *ip, const struct sshkey *key,
char **user_hostfiles, u_int num_user_hostfiles,
char **system_hostfiles, u_int num_system_hostfiles,
char ***names, u_int *nnames)
{
struct find_by_key_ctx ctx = {0};
u_int i;
*names = NULL;
*nnames = 0;
if (key == NULL || sshkey_is_cert(key))
return;
ctx.host = host;
ctx.ip = ip;
ctx.key = key;
for (i = 0; i < num_user_hostfiles; i++) {
if (hostkeys_find_by_key_hostfile(user_hostfiles[i],
"user", &ctx) != 0)
goto fail;
}
for (i = 0; i < num_system_hostfiles; i++) {
if (hostkeys_find_by_key_hostfile(system_hostfiles[i],
"system", &ctx) != 0)
goto fail;
}
/* success */
*names = ctx.names;
*nnames = ctx.nnames;
ctx.names = NULL;
ctx.nnames = 0;
return;
fail:
for (i = 0; i < ctx.nnames; i++)
free(ctx.names[i]);
free(ctx.names);
}
#define MAX_OTHER_NAMES 8 /* Maximum number of names to list */
static char *
other_hostkeys_message(const char *host, const char *ip,
const struct sshkey *key,
char **user_hostfiles, u_int num_user_hostfiles,
char **system_hostfiles, u_int num_system_hostfiles)
{
char *ret = NULL, **othernames = NULL;
u_int i, n, num_othernames = 0;
hostkeys_find_by_key(host, ip, key,
user_hostfiles, num_user_hostfiles,
system_hostfiles, num_system_hostfiles,
&othernames, &num_othernames);
if (num_othernames == 0)
return xstrdup("This key is not known by any other names");
xasprintf(&ret, "This host key is known by the following other "
"names/addresses:");
n = num_othernames;
if (n > MAX_OTHER_NAMES)
n = MAX_OTHER_NAMES;
for (i = 0; i < n; i++) {
xextendf(&ret, "\n", " %s", othernames[i]);
}
if (n < num_othernames) {
xextendf(&ret, "\n", " (%d additional names ommitted)",
num_othernames - n);
}
for (i = 0; i < num_othernames; i++)
free(othernames[i]);
free(othernames);
return ret;
}
/*
* check whether the supplied host key is valid, return -1 if the key
* is not valid. user_hostfile[0] will not be updated if 'readonly' is true.
@ -876,45 +1036,48 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
goto fail;
} else if (options.strict_host_key_checking ==
SSH_STRICT_HOSTKEY_ASK) {
char msg1[1024], msg2[1024];
char *msg1 = NULL, *msg2 = NULL;
xasprintf(&msg1, "The authenticity of host "
"'%.200s (%s)' can't be established", host, ip);
if (show_other_keys(host_hostkeys, host_key)) {
xextendf(&msg1, "\n", "but keys of different "
"type are already known for this host.");
} else
xextendf(&msg1, "", ".");
if (show_other_keys(host_hostkeys, host_key))
snprintf(msg1, sizeof(msg1),
"\nbut keys of different type are already"
" known for this host.");
else
snprintf(msg1, sizeof(msg1), ".");
/* The default */
fp = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
ra = sshkey_fingerprint(host_key,
options.fingerprint_hash, SSH_FP_RANDOMART);
if (fp == NULL || ra == NULL)
fatal_f("sshkey_fingerprint failed");
msg2[0] = '\0';
xextendf(&msg1, "\n", "%s key fingerprint is %s.",
type, fp);
if (options.visual_host_key)
xextendf(&msg1, "\n", "%s", ra);
if (options.verify_host_key_dns) {
if (matching_host_key_dns)
snprintf(msg2, sizeof(msg2),
"Matching host key fingerprint"
" found in DNS.\n");
else
snprintf(msg2, sizeof(msg2),
"No matching host key fingerprint"
" found in DNS.\n");
xextendf(&msg1, "\n",
"%s host key fingerprint found in DNS.",
matching_host_key_dns ?
"Matching" : "No matching");
}
snprintf(msg, sizeof(msg),
"The authenticity of host '%.200s (%s)' can't be "
"established%s\n"
"%s key fingerprint is %s.%s%s\n%s"
/* msg2 informs for other names matching this key */
if ((msg2 = other_hostkeys_message(host, ip, host_key,
user_hostfiles, num_user_hostfiles,
system_hostfiles, num_system_hostfiles)) != NULL)
xextendf(&msg1, "\n", "%s", msg2);
xextendf(&msg1, "\n",
"Are you sure you want to continue connecting "
"(yes/no/[fingerprint])? ",
host, ip, msg1, type, fp,
options.visual_host_key ? "\n" : "",
options.visual_host_key ? ra : "",
msg2);
"(yes/no/[fingerprint])? ");
confirmed = confirm(msg1, fp);
free(ra);
confirmed = confirm(msg, fp);
free(fp);
free(msg1);
free(msg2);
if (!confirmed)
goto fail;
hostkey_trusted = 1; /* user explicitly confirmed */