From e3296cc796aeaf319f3ed4e064ec309baf5e4da4 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Mon, 13 Sep 2021 17:59:00 +0100 Subject: [PATCH] block: print the server key type and fingerprint on failure MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When validating the server key fingerprint fails, it is difficult for the user to know what they got wrong. The fingerprint accepted by QEMU is received in a different format than OpenSSH displays. There can also be keys for multiple different ciphers in known_hosts. It may not be obvious which cipher QEMU will use and whether it will be the same as OpenSSH. Address this by printing the server key type and its corresponding fingerprint in the format QEMU accepts. Reviewed-by: Hanna Reitz Reviewed-by: Philippe Mathieu-Daudé Signed-off-by: Daniel P. Berrangé --- block/ssh.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) diff --git a/block/ssh.c b/block/ssh.c index ac01301409..a64db146db 100644 --- a/block/ssh.c +++ b/block/ssh.c @@ -386,14 +386,28 @@ static int compare_fingerprint(const unsigned char *fingerprint, size_t len, return *host_key_check - '\0'; } +static char *format_fingerprint(const unsigned char *fingerprint, size_t len) +{ + static const char *hex = "0123456789abcdef"; + char *ret = g_new0(char, (len * 2) + 1); + for (size_t i = 0; i < len; i++) { + ret[i * 2] = hex[((fingerprint[i] >> 4) & 0xf)]; + ret[(i * 2) + 1] = hex[(fingerprint[i] & 0xf)]; + } + ret[len * 2] = '\0'; + return ret; +} + static int check_host_key_hash(BDRVSSHState *s, const char *hash, - enum ssh_publickey_hash_type type, Error **errp) + enum ssh_publickey_hash_type type, const char *typestr, + Error **errp) { int r; ssh_key pubkey; unsigned char *server_hash; size_t server_hash_len; + const char *keytype; r = ssh_get_server_publickey(s->session, &pubkey); if (r != SSH_OK) { @@ -401,6 +415,8 @@ check_host_key_hash(BDRVSSHState *s, const char *hash, return -EINVAL; } + keytype = ssh_key_type_to_char(ssh_key_type(pubkey)); + r = ssh_get_publickey_hash(pubkey, type, &server_hash, &server_hash_len); ssh_key_free(pubkey); if (r != 0) { @@ -410,12 +426,16 @@ check_host_key_hash(BDRVSSHState *s, const char *hash, } r = compare_fingerprint(server_hash, server_hash_len, hash); - ssh_clean_pubkey_hash(&server_hash); if (r != 0) { - error_setg(errp, "remote host key does not match host_key_check '%s'", - hash); + g_autofree char *server_fp = format_fingerprint(server_hash, + server_hash_len); + error_setg(errp, "remote host %s key fingerprint '%s:%s' " + "does not match host_key_check '%s:%s'", + keytype, typestr, server_fp, typestr, hash); + ssh_clean_pubkey_hash(&server_hash); return -EPERM; } + ssh_clean_pubkey_hash(&server_hash); return 0; } @@ -436,13 +456,16 @@ static int check_host_key(BDRVSSHState *s, SshHostKeyCheck *hkc, Error **errp) case SSH_HOST_KEY_CHECK_MODE_HASH: if (hkc->u.hash.type == SSH_HOST_KEY_CHECK_HASH_TYPE_MD5) { return check_host_key_hash(s, hkc->u.hash.hash, - SSH_PUBLICKEY_HASH_MD5, errp); + SSH_PUBLICKEY_HASH_MD5, "md5", + errp); } else if (hkc->u.hash.type == SSH_HOST_KEY_CHECK_HASH_TYPE_SHA1) { return check_host_key_hash(s, hkc->u.hash.hash, - SSH_PUBLICKEY_HASH_SHA1, errp); + SSH_PUBLICKEY_HASH_SHA1, "sha1", + errp); } else if (hkc->u.hash.type == SSH_HOST_KEY_CHECK_HASH_TYPE_SHA256) { return check_host_key_hash(s, hkc->u.hash.hash, - SSH_PUBLICKEY_HASH_SHA256, errp); + SSH_PUBLICKEY_HASH_SHA256, "sha256", + errp); } g_assert_not_reached(); break; -- 2.30.2