From: =?UTF-8?q?Carlos=20Mart=C3=ADn=20Nieto?= Date: Tue, 1 Nov 2022 12:54:29 +0100 Subject: [PATCH] Fix CVE-2023-22742 Upstream(1.4.x): https://github.com/libgit2/libgit2/pull/6449 Origin: https://build.opensuse.org/package/show/SUSE:SLE-15-SP4:Update/libgit2.28263 --- src/transports/ssh.c | 417 ++++++++++++++++++++++++++++++++++--------- 1 files changed, 329 insertions(+), 88 deletions(-) diff --git a/ci/test.sh b/ci/test.sh index 2aed691..743dbdf 100755 --- a/ci/test.sh +++ b/ci/test.sh @@ -143,6 +143,11 @@ if [ -z "$SKIP_SSH_TESTS" ]; then echo "[localhost]:2222 $algorithm $key" >>"${HOME}/.ssh/known_hosts" done <"${SSHD_DIR}/id_rsa.pub" + # Append the github.com keys for the tests that don't override checks. + # We ask for ssh-rsa to test that the selection based off of known_hosts + # is working. + ssh-keyscan -t ssh-rsa github.com >>"${HOME}/.ssh/known_hosts" + # Get the fingerprint for localhost and remove the colons so we can # parse it as a hex number. Older versions have a different output # format. diff --git a/src/transports/ssh.c b/src/transports/ssh.c index 1b00be7..86cfcc9 100644 --- a/src/transports/ssh.c +++ b/src/transports/ssh.c @@ -475,15 +475,118 @@ static int request_creds(git_credential **out, ssh_subtransport *t, const char * return 0; } +#define KNOWN_HOSTS_FILE ".ssh/known_hosts" + +/* + * Load the known_hosts file. + * + * Returns success but leaves the output NULL if we couldn't find the file. + */ +static int load_known_hosts(LIBSSH2_KNOWNHOSTS **hosts, LIBSSH2_SESSION *session) +{ + char *path = NULL; + const char *home; + LIBSSH2_KNOWNHOSTS *known_hosts = NULL; + int error; + + GIT_ASSERT_ARG(hosts); + + home = getenv ("HOME"); + if (!home) + return -1; + path = (char *) malloc (strlen (home) + strlen (KNOWN_HOSTS_FILE) + 2); + sprintf (path, "%s/%s", home, KNOWN_HOSTS_FILE); + + if ((known_hosts = libssh2_knownhost_init(session)) == NULL) { + ssh_error(session, "error initializing known hosts"); + error = -1; + goto out; + } + + /* + * Try to read the file and consider not finding it as not trusting the + * host rather than an error. + */ + error = libssh2_knownhost_readfile(known_hosts, path, LIBSSH2_KNOWNHOST_FILE_OPENSSH); + if (error == LIBSSH2_ERROR_FILE) + error = 0; + if (error < 0) + ssh_error(session, "error reading known_hosts"); + +out: + *hosts = known_hosts; + free (path); + + return error; +} + +static const char *hostkey_type_to_string(int type) +{ + switch (type) { + case LIBSSH2_KNOWNHOST_KEY_SSHRSA: + return "ssh-rsa"; + case LIBSSH2_KNOWNHOST_KEY_SSHDSS: + return "ssh-dss"; +#ifdef LIBSSH2_KNOWNHOST_KEY_ECDSA_256 + case LIBSSH2_KNOWNHOST_KEY_ECDSA_256: + return "ecdsa-sha2-nistp256"; + case LIBSSH2_KNOWNHOST_KEY_ECDSA_384: + return "ecdsa-sha2-nistp384"; + case LIBSSH2_KNOWNHOST_KEY_ECDSA_521: + return "ecdsa-sha2-nistp521"; +#endif +#ifdef LIBSSH2_KNOWNHOST_KEY_ED25519 + case LIBSSH2_KNOWNHOST_KEY_ED25519: + return "ssh-ed25519"; +#endif + } + + return NULL; +} + +/* + * We figure out what kind of key we want to ask the remote for by trying to + * look it up with a nonsense key and using that mismatch to figure out what key + * we do have stored for the host. + * + * Returns the string to pass to libssh2_session_method_pref or NULL if we were + * unable to find anything or an error happened. + */ +static const char *find_hostkey_preference(LIBSSH2_KNOWNHOSTS *known_hosts, const char *hostname, int port) +{ + struct libssh2_knownhost *host = NULL; + /* Specify no key type so we don't filter on that */ + int type = LIBSSH2_KNOWNHOST_TYPE_PLAIN | LIBSSH2_KNOWNHOST_KEYENC_RAW; + const char key = '\0'; + int error; + + /* + * In case of mismatch, we can find the type of key from known_hosts in + * the returned host's information as it means that an entry was found + * but our nonsense key obviously didn't match. + */ + error = libssh2_knownhost_checkp(known_hosts, hostname, port, &key, 1, type, &host); + if (error == LIBSSH2_KNOWNHOST_CHECK_MISMATCH) + return hostkey_type_to_string(host->typemask & LIBSSH2_KNOWNHOST_KEY_MASK); + + return NULL; +} + static int _git_ssh_session_create( LIBSSH2_SESSION **session, + LIBSSH2_KNOWNHOSTS **hosts, + const char *hostname, + int port, git_stream *io) { int rc = 0; LIBSSH2_SESSION *s; + LIBSSH2_KNOWNHOSTS *known_hosts; git_socket_stream *socket = GIT_CONTAINER_OF(io, git_socket_stream, parent); + const char *keytype = NULL; GIT_ASSERT_ARG(session); + GIT_ASSERT_ARG(hosts); s = libssh2_session_init(); if (!s) { @@ -491,21 +594,228 @@ static int _git_ssh_session_create( return -1; } + if ((rc = load_known_hosts(&known_hosts, s)) < 0) { + ssh_error(s, "error loading known_hosts"); + libssh2_session_free(s); + return -1; + } + + if ((keytype = find_hostkey_preference(known_hosts, hostname, port)) != NULL) { + do { + rc = libssh2_session_method_pref(s, LIBSSH2_METHOD_HOSTKEY, keytype); + } while (LIBSSH2_ERROR_EAGAIN == rc || LIBSSH2_ERROR_TIMEOUT == rc); + if (rc != LIBSSH2_ERROR_NONE) { + ssh_error(s, "failed to set hostkey preference"); + goto on_error; + } + } + + do { rc = libssh2_session_handshake(s, socket->s); } while (LIBSSH2_ERROR_EAGAIN == rc || LIBSSH2_ERROR_TIMEOUT == rc); if (rc != LIBSSH2_ERROR_NONE) { ssh_error(s, "failed to start SSH session"); - libssh2_session_free(s); - return -1; + goto on_error; } libssh2_session_set_blocking(s, 1); *session = s; + *hosts = known_hosts; return 0; + +on_error: + libssh2_knownhost_free(known_hosts); + libssh2_session_free(s); + return -1; +} + + +/* + * Returns the typemask argument to pass to libssh2_knownhost_check{,p} based on + * the type of key that libssh2_session_hostkey returns. + */ +static int fingerprint_type_mask(int keytype) +{ + int mask = LIBSSH2_KNOWNHOST_TYPE_PLAIN | LIBSSH2_KNOWNHOST_KEYENC_RAW; + return mask; + + switch (keytype) { + case LIBSSH2_HOSTKEY_TYPE_RSA: + mask |= LIBSSH2_KNOWNHOST_KEY_SSHRSA; + break; + case LIBSSH2_HOSTKEY_TYPE_DSS: + mask |= LIBSSH2_KNOWNHOST_KEY_SSHDSS; + break; +#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_256 + case LIBSSH2_HOSTKEY_TYPE_ECDSA_256: + mask |= LIBSSH2_KNOWNHOST_KEY_ECDSA_256; + break; + case LIBSSH2_HOSTKEY_TYPE_ECDSA_384: + mask |= LIBSSH2_KNOWNHOST_KEY_ECDSA_384; + break; + case LIBSSH2_HOSTKEY_TYPE_ECDSA_521: + mask |= LIBSSH2_KNOWNHOST_KEY_ECDSA_521; + break; +#endif +#ifdef LIBSSH2_HOSTKEY_TYPE_ED25519 + case LIBSSH2_HOSTKEY_TYPE_ED25519: + mask |= LIBSSH2_KNOWNHOST_KEY_ED25519; + break; +#endif + } + + return mask; +} + +/* + * Check the host against the user's known_hosts file. + * + * Returns 1/0 for valid/''not-valid or <0 for an error + */ +static int check_against_known_hosts( + LIBSSH2_SESSION *session, + LIBSSH2_KNOWNHOSTS *known_hosts, + const char *hostname, + int port, + const char *key, + size_t key_len, + int key_type) +{ + int check, typemask, ret = 0; + struct libssh2_knownhost *host = NULL; + + if (known_hosts == NULL) + return 0; + + typemask = fingerprint_type_mask(key_type); + check = libssh2_knownhost_checkp(known_hosts, hostname, port, key, key_len, typemask, &host); + if (check == LIBSSH2_KNOWNHOST_CHECK_FAILURE) { + ssh_error(session, "error checking for known host"); + return -1; + } + + ret = check == LIBSSH2_KNOWNHOST_CHECK_MATCH ? 1 : 0; + +out: + libssh2_knownhost_free(known_hosts); + + return ret; +} + +/* + * Perform the check for the session's certificate against known hosts if + * possible and then ask the user if they have a callback. + * + * Returns 1/0 for valid/not-valid or <0 for an error + */ +static int check_certificate( + LIBSSH2_SESSION *session, + LIBSSH2_KNOWNHOSTS *known_hosts, + git_transport_certificate_check_cb check_cb, + void *check_cb_payload, + const char *host, + int port) +{ + git_cert_hostkey cert = {{ 0 }}; + const char *key; + size_t cert_len; + int cert_type, cert_valid = 0, error = 0; + + if ((key = libssh2_session_hostkey(session, &cert_len, &cert_type)) == NULL) { + ssh_error(session, "failed to retrieve hostkey"); + return -1; + } + + if ((cert_valid = check_against_known_hosts(session, known_hosts, host, port, key, cert_len, cert_type)) < 0) + return -1; + + cert.parent.cert_type = GIT_CERT_HOSTKEY_LIBSSH2; + if (key != NULL) { + cert.type |= GIT_CERT_SSH_RAW; + cert.hostkey = key; + cert.hostkey_len = cert_len; + switch (cert_type) { + case LIBSSH2_HOSTKEY_TYPE_RSA: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_RSA; + break; + case LIBSSH2_HOSTKEY_TYPE_DSS: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_DSS; + break; + +#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_256 + case LIBSSH2_HOSTKEY_TYPE_ECDSA_256: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_256; + break; + case LIBSSH2_HOSTKEY_TYPE_ECDSA_384: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_384; + break; + case LIBSSH2_KNOWNHOST_KEY_ECDSA_521: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_521; + break; +#endif + +#ifdef LIBSSH2_HOSTKEY_TYPE_ED25519 + case LIBSSH2_HOSTKEY_TYPE_ED25519: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ED25519; + break; +#endif + default: + cert.raw_type = GIT_CERT_SSH_RAW_TYPE_UNKNOWN; + } + } + +#ifdef LIBSSH2_HOSTKEY_HASH_SHA256 + key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA256); + if (key != NULL) { + cert.type |= GIT_CERT_SSH_SHA256; + memcpy(&cert.hash_sha256, key, 32); + } +#endif + + key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA1); + if (key != NULL) { + cert.type |= GIT_CERT_SSH_SHA1; + memcpy(&cert.hash_sha1, key, 20); + } + + key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_MD5); + if (key != NULL) { + cert.type |= GIT_CERT_SSH_MD5; + memcpy(&cert.hash_md5, key, 16); + } + + if (cert.type == 0) { + git_error_set(GIT_ERROR_SSH, "unable to get the host key"); + return -1; + } + + git_error_clear(); + error = 0; + if (!cert_valid) { + git_error_set(GIT_ERROR_SSH, "invalid or unknown remote ssh hostkey"); + error = GIT_ECERTIFICATE; + } + + if (check_cb != NULL) { + git_cert_hostkey *cert_ptr = &cert; + git_error_state previous_error = {0}; + + git_error_state_capture(&previous_error, error); + error = check_cb((git_cert *) cert_ptr, cert_valid, host, check_cb_payload); + if (error == GIT_PASSTHROUGH) { + error = git_error_state_restore(&previous_error); + } else if (error < 0 && !git_error_last()) { + git_error_set(GIT_ERROR_NET, "user canceled hostkey check"); + } + + git_error_state_free(&previous_error); + } + + return error; } #define SSH_DEFAULT_PORT "22" @@ -517,12 +827,13 @@ static int _git_ssh_setup_conn( git_smart_subtransport_stream **stream) { git_net_url urldata = GIT_NET_URL_INIT; - int auth_methods, error = 0; + int auth_methods, error = 0, port; size_t i; ssh_stream *s; git_credential *cred = NULL; LIBSSH2_SESSION *session=NULL; LIBSSH2_CHANNEL *channel=NULL; + LIBSSH2_KNOWNHOSTS *known_hosts = NULL; t->current_stream = NULL; @@ -557,93 +868,21 @@ post_extract: (error = git_stream_connect(s->io)) < 0) goto done; - if ((error = _git_ssh_session_create(&session, s->io)) < 0) - goto done; - - if (t->owner->certificate_check_cb != NULL) { - git_cert_hostkey cert = {{ 0 }}, *cert_ptr; - const char *key; - size_t cert_len; - int cert_type; - - cert.parent.cert_type = GIT_CERT_HOSTKEY_LIBSSH2; - - key = libssh2_session_hostkey(session, &cert_len, &cert_type); - if (key != NULL) { - cert.type |= GIT_CERT_SSH_RAW; - cert.hostkey = key; - cert.hostkey_len = cert_len; - switch (cert_type) { - case LIBSSH2_HOSTKEY_TYPE_RSA: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_RSA; - break; - case LIBSSH2_HOSTKEY_TYPE_DSS: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_DSS; - break; - -#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_256 - case LIBSSH2_HOSTKEY_TYPE_ECDSA_256: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_256; - break; - case LIBSSH2_HOSTKEY_TYPE_ECDSA_384: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_384; - break; - case LIBSSH2_KNOWNHOST_KEY_ECDSA_521: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_521; - break; -#endif - -#ifdef LIBSSH2_HOSTKEY_TYPE_ED25519 - case LIBSSH2_HOSTKEY_TYPE_ED25519: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ED25519; - break; -#endif - default: - cert.raw_type = GIT_CERT_SSH_RAW_TYPE_UNKNOWN; - } - } - -#ifdef LIBSSH2_HOSTKEY_HASH_SHA256 - key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA256); - if (key != NULL) { - cert.type |= GIT_CERT_SSH_SHA256; - memcpy(&cert.hash_sha256, key, 32); - } -#endif - - key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA1); - if (key != NULL) { - cert.type |= GIT_CERT_SSH_SHA1; - memcpy(&cert.hash_sha1, key, 20); - } - - key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_MD5); - if (key != NULL) { - cert.type |= GIT_CERT_SSH_MD5; - memcpy(&cert.hash_md5, key, 16); - } - - if (cert.type == 0) { - git_error_set(GIT_ERROR_SSH, "unable to get the host key"); - error = -1; - goto done; - } - - /* We don't currently trust any hostkeys */ - git_error_clear(); - - cert_ptr = &cert; - - error = t->owner->certificate_check_cb((git_cert *) cert_ptr, 0, urldata.host, t->owner->message_cb_payload); - - if (error < 0 && error != GIT_PASSTHROUGH) { - if (!git_error_last()) - git_error_set(GIT_ERROR_NET, "user cancelled hostkey check"); + /* + * Try to parse the port as a number, if we can't then fall back to + * default. It would be nice if we could get the port that was resolved + * as part of the stream connection, but that's not something that's + * exposed. + */ + if (git__strntol32(&port, urldata.port, strlen(urldata.port), NULL, 10) < 0) + port = -1; - goto done; - } - } + if ((error = _git_ssh_session_create(&session, &known_hosts, urldata.host, port, s->io)) < 0) + goto done; + if ((error = check_certificate(session, known_hosts, t->owner->certificate_check_cb, t->owner->message_cb_payload, urldata.host, urldata.port)) < 0) + goto done; + /* we need the username to ask for auth methods */ if (!urldata.username) { if ((error = request_creds(&cred, t, NULL, GIT_CREDENTIAL_USERNAME)) < 0) @@ -714,6 +953,8 @@ done: if (error < 0) { ssh_stream_free(*stream); + if (known_hosts) + libssh2_knownhost_free(known_hosts); if (session) libssh2_session_free(session); } -- 2.33.0