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diff -up openssh-8.0p1/hostfile.c.cve-2020-14145 openssh-8.0p1/hostfile.c
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--- openssh-8.0p1/hostfile.c.cve-2020-14145 2019-04-18 00:52:57.000000000 +0200
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+++ openssh-8.0p1/hostfile.c 2021-05-17 16:53:38.694577251 +0200
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@@ -409,6 +409,18 @@ lookup_key_in_hostkeys_by_type(struct ho
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found) == HOST_FOUND);
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}
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+int
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+lookup_marker_in_hostkeys(struct hostkeys *hostkeys, int want_marker)
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+{
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+ u_int i;
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+
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+ for (i = 0; i < hostkeys->num_entries; i++) {
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+ if (hostkeys->entries[i].marker == (HostkeyMarker)want_marker)
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+ return 1;
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+ }
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+ return 0;
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+}
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+
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static int
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write_host_entry(FILE *f, const char *host, const char *ip,
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const struct sshkey *key, int store_hash)
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diff -up openssh-8.0p1/hostfile.h.cve-2020-14145 openssh-8.0p1/hostfile.h
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--- openssh-8.0p1/hostfile.h.cve-2020-14145 2019-04-18 00:52:57.000000000 +0200
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+++ openssh-8.0p1/hostfile.h 2021-05-17 16:53:38.694577251 +0200
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@@ -39,6 +39,7 @@ HostStatus check_key_in_hostkeys(struct
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const struct hostkey_entry **);
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int lookup_key_in_hostkeys_by_type(struct hostkeys *, int,
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const struct hostkey_entry **);
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+int lookup_marker_in_hostkeys(struct hostkeys *, int);
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int hostfile_read_key(char **, u_int *, struct sshkey *);
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int add_host_to_hostfile(const char *, const char *,
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diff -up openssh-8.0p1/sshconnect2.c.cve-2020-14145 openssh-8.0p1/sshconnect2.c
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--- openssh-8.0p1/sshconnect2.c.cve-2020-14145 2021-05-17 16:53:38.610576561 +0200
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+++ openssh-8.0p1/sshconnect2.c 2021-05-17 16:54:58.169230103 +0200
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@@ -98,12 +98,25 @@ verify_host_key_callback(struct sshkey *
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return 0;
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}
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+/* Returns the first item from a comma-separated algorithm list */
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+static char *
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+first_alg(const char *algs)
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+{
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+ char *ret, *cp;
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+
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+ ret = xstrdup(algs);
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+ if ((cp = strchr(ret, ',')) != NULL)
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+ *cp = '\0';
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+ return ret;
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+}
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+
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static char *
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order_hostkeyalgs(char *host, struct sockaddr *hostaddr, u_short port)
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{
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- char *oavail, *avail, *first, *last, *alg, *hostname, *ret;
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+ char *oavail = NULL, *avail = NULL, *first = NULL, *last = NULL;
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+ char *alg = NULL, *hostname = NULL, *ret = NULL, *best = NULL;
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size_t maxlen;
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- struct hostkeys *hostkeys;
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+ struct hostkeys *hostkeys = NULL;
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int ktype;
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u_int i;
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7afad6 |
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@@ -115,6 +128,26 @@ order_hostkeyalgs(char *host, struct soc
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for (i = 0; i < options.num_system_hostfiles; i++)
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load_hostkeys(hostkeys, hostname, options.system_hostfiles[i]);
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+ /*
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+ * If a plain public key exists that matches the type of the best
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+ * preference HostkeyAlgorithms, then use the whole list as is.
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+ * Note that we ignore whether the best preference algorithm is a
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+ * certificate type, as sshconnect.c will downgrade certs to
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+ * plain keys if necessary.
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+ */
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+ best = first_alg(options.hostkeyalgorithms);
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+ if (lookup_key_in_hostkeys_by_type(hostkeys,
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+ sshkey_type_plain(sshkey_type_from_name(best)), NULL)) {
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+ debug3("%s: have matching best-preference key type %s, "
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+ "using HostkeyAlgorithms verbatim", __func__, best);
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+ ret = xstrdup(options.hostkeyalgorithms);
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+ goto out;
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+ }
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7afad6 |
+
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+ /*
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+ * Otherwise, prefer the host key algorithms that match known keys
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+ * while keeping the ordering of HostkeyAlgorithms as much as possible.
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+ */
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oavail = avail = xstrdup(KEX_DEFAULT_PK_ALG);
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maxlen = strlen(avail) + 1;
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first = xmalloc(maxlen);
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7afad6 |
@@ -131,11 +164,23 @@ order_hostkeyalgs(char *host, struct soc
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while ((alg = strsep(&avail, ",")) && *alg != '\0') {
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if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
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fatal("%s: unknown alg %s", __func__, alg);
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+ /*
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+ * If we have a @cert-authority marker in known_hosts then
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+ * prefer all certificate algorithms.
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+ */
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+ if (sshkey_type_is_cert(ktype) &&
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+ lookup_marker_in_hostkeys(hostkeys, MRK_CA)) {
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+ ALG_APPEND(first, alg);
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+ continue;
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+ }
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+ /* If the key appears in known_hosts then prefer it */
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if (lookup_key_in_hostkeys_by_type(hostkeys,
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- sshkey_type_plain(ktype), NULL))
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+ sshkey_type_plain(ktype), NULL)) {
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ALG_APPEND(first, alg);
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- else
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- ALG_APPEND(last, alg);
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+ continue;
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+ }
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+ /* Otherwise, put it last */
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+ ALG_APPEND(last, alg);
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}
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7afad6 |
#undef ALG_APPEND
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7afad6 |
xasprintf(&ret, "%s%s%s", first,
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7afad6 |
@@ -143,6 +188,8 @@ order_hostkeyalgs(char *host, struct soc
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7afad6 |
if (*first != '\0')
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7afad6 |
debug3("%s: prefer hostkeyalgs: %s", __func__, first);
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7afad6 |
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7afad6 |
+ out:
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7afad6 |
+ free(best);
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7afad6 |
free(first);
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7afad6 |
free(last);
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7afad6 |
free(hostname);
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