File 0004-ssh-look-for-a-key-in-known_hosts-to-set-the-key-typ.patch of Package libgit2.28344
From 63b083e5d8ecea0750eb5767018b1cdad94c2382 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carlos=20Mart=C3=ADn=20Nieto?= <carlosmn@github.com>
Date: Wed, 2 Nov 2022 13:47:25 +0100
Subject: [PATCH 4/6] ssh: look for a key in known_hosts to set the key type
for the handshake
The server and client negotiate a single hostkey, but the "best" cipher may not
be the one for which we have an entry in `known_hosts`. This can lead to us not
finding the key in known_hosts even though we should be connecting.
Instead here we look up the hostname with a nonsense key to perform a lookup in
the known hosts and set that. This is roughly what the OpenSSH client does as
well.
---
src/transports/ssh.c | 206 ++++++++++++++++++++++++++++++++-----------
1 file changed, 153 insertions(+), 53 deletions(-)
diff -urp libgit2-0.28.4.orig/src/transports/ssh.c libgit2-0.28.4/src/transports/ssh.c
--- libgit2-0.28.4.orig/src/transports/ssh.c 2023-03-16 15:16:19.777966468 -0500
+++ libgit2-0.28.4/src/transports/ssh.c 2023-03-16 15:29:42.250202516 -0500
@@ -473,15 +473,120 @@ static int request_creds(git_cred **out,
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;
+
+ assert(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;
+
+ if (path)
+ 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_socket_stream *) io;
+ const char *keytype = NULL;
assert(session);
+ assert(hosts);
s = libssh2_session_init();
if (!s) {
@@ -489,23 +594,46 @@ 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.
@@ -543,8 +671,6 @@ static int fingerprint_type_mask(int key
return mask;
}
-#define KNOWN_HOSTS_FILE ".ssh/known_hosts"
-
/*
* Check the host against the user's known_hosts file.
*
@@ -552,62 +678,28 @@ static int fingerprint_type_mask(int key
*/
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 error, check, typemask, ret = 0;
- git_str path = GIT_STR_INIT, home = GIT_STR_INIT;
- LIBSSH2_KNOWNHOSTS *known_hosts = NULL;
+ int check, typemask, ret = 0;
struct libssh2_knownhost *host = NULL;
- if ((error = git__getenv(&home, "HOME")) < 0) {
- return error;
- }
-
- if ((error = git_str_joinpath(&path, git_str_cstr(&home), KNOWN_HOSTS_FILE)) < 0) {
- ret = error;
- goto out;
- }
-
- if ((known_hosts = libssh2_knownhost_init(session)) == NULL) {
- ssh_error(session, "error initializing known hosts");
- ret = -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, git_str_cstr(&path), LIBSSH2_KNOWNHOST_FILE_OPENSSH);
- if (error == LIBSSH2_ERROR_FILE) {
- ret = 0;
- goto out;
- }
- if (error < 0) {
- ssh_error(session, "error reading known_hosts");
- ret = -1;
- goto out;
- }
+ 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");
- ret = -1;
- goto out;
+ return -1;
}
ret = check == LIBSSH2_KNOWNHOST_CHECK_MATCH ? 1 : 0;
-out:
- libssh2_knownhost_free(known_hosts);
- git_str_clear(&path);
- git_str_clear(&home);
-
return ret;
}
@@ -619,26 +711,23 @@ out:
*/
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,
- const char *portstr)
+ int port)
{
git_cert_hostkey cert = {{ 0 }};
const char *key;
size_t cert_len;
- int cert_type, port, cert_valid = 0, error = 0;
+ 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;
}
- /* Try to parse the port as a number, if we can't then fall back to default */
- if (git__strntol32(&port, portstr, strlen(portstr), NULL, 10) < 0)
- port = -1;
-
- if ((cert_valid = check_against_known_hosts(session, host, port, key, cert_len, cert_type)) < 0)
+ 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;
@@ -692,12 +781,13 @@ static int _git_ssh_setup_conn(
{
char *host=NULL, *port=NULL, *path=NULL, *user=NULL, *pass=NULL;
const char *default_port="22";
- int auth_methods, error = 0;
+ int auth_methods, error = 0, port_num;
size_t i;
ssh_stream *s;
git_cred *cred = NULL;
LIBSSH2_SESSION* session=NULL;
LIBSSH2_CHANNEL* channel=NULL;
+ LIBSSH2_KNOWNHOSTS *known_hosts = NULL;
t->current_stream = NULL;
@@ -729,10 +819,19 @@ post_extract:
(error = git_stream_connect(s->io)) < 0)
goto done;
- if ((error = _git_ssh_session_create(&session, s->io)) < 0)
+ /*
+ * 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_num, port, strlen(port), NULL, 10) < 0)
+ port_num = -1;
+
+ if ((error = _git_ssh_session_create(&session, &known_hosts, host, port, s->io)) < 0)
goto done;
- if ((error = check_certificate(session, t->owner->certificate_check_cb, t->owner->message_cb_payload, host, port)) < 0)
+ if ((error = check_certificate(session, known_hosts, t->owner->certificate_check_cb, t->owner->message_cb_payload, host, port)) < 0)
goto done;
/* we need the username to ask for auth methods */
@@ -797,6 +896,8 @@ done:
if (error < 0) {
ssh_stream_free(*stream);
+ if (known_hosts)
+ libssh2_knownhost_free(known_hosts);
if (session)
libssh2_session_free(session);
}
