upstream: ssh-keygen -Y find-principals fixes based on feedback

from Markus:

use "principals" instead of principal, as allowed_signers lines may list
multiple.

When the signing key is a certificate, emit only principals that match
the certificate principal list.

NB. the command -Y name changes: "find-principal" => "find-principals"

ok markus@

OpenBSD-Commit-ID: ab575946ff9a55624cd4e811bfd338bf3b1d0faf

1 files changed, 63 insertions, 11 deletions

diff --git a/sshsig.c b/sshsig.c
index e9f4baa76..e63a36e1e 100644
--- a/sshsig.c
+++ b/sshsig.c
@@ -868,13 +868,64 @@ sshsig_check_allowed_keys(const char *path, const struct sshkey *sign_key,
 }
 
 static int
-get_matching_principal_from_line(const char *path, u_long linenum, char *line,
+cert_filter_principals(const char *path, u_long linenum,
+    char **principalsp, const struct sshkey *cert)
+{
+        char *cp, *oprincipals, *principals;
+        const char *reason;
+        struct sshbuf *nprincipals;
+        int r = SSH_ERR_INTERNAL_ERROR, success = 0;
+
+        oprincipals = principals = *principalsp;
+        *principalsp = NULL;
+
+        if ((nprincipals = sshbuf_new()) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
+
+        while ((cp = strsep(&principals, ",")) != NULL && *cp != '\0') {
+                if (strcspn(cp, "!?*") != strlen(cp)) {
+                        debug("%s:%lu: principal \"%s\" not authorized: "
+                            "contains wildcards", path, linenum, cp);
+                        continue;
+                }
+                /* Check against principals list in certificate */
+                if ((r = sshkey_cert_check_authority(cert, 0, 1,
+                    cp, &reason)) != 0) {
+                        debug("%s:%lu: principal \"%s\" not authorized: %s",
+                            path, linenum, cp, reason);
+                        continue;
+                }
+                if ((r = sshbuf_putf(nprincipals, "%s%s",
+                    sshbuf_len(nprincipals) != 0 ? "," : "", cp)) != 0) {
+                        error("%s: buffer error", __func__);
+                        goto out;
+                }
+        }
+        if (sshbuf_len(nprincipals) == 0) {
+                error("%s:%lu: no valid principals found", path, linenum);
+                r = SSH_ERR_KEY_CERT_INVALID;
+                goto out;
+        }
+        if ((principals = sshbuf_dup_string(nprincipals)) == NULL) {
+                error("%s: buffer error", __func__);
+                goto out;
+        }
+        /* success */
+        success = 1;
+        *principalsp = principals;
+ out:
+        sshbuf_free(nprincipals);
+        free(oprincipals);
+        return success ? 0 : r;
+}
+
+static int
+get_matching_principals_from_line(const char *path, u_long linenum, char *line,
     const struct sshkey *sign_key, char **principalsp)
 {
         struct sshkey *found_key = NULL;
         char *principals = NULL;
         int r, found = 0;
-        const char *reason = NULL;
         struct sshsigopt *sigopts = NULL;
 
         if (principalsp != NULL)
@@ -894,11 +945,12 @@ get_matching_principal_from_line(const char *path, u_long linenum, char *line,
                 found = 1;
         } else if (sigopts->ca && sshkey_is_cert(sign_key) &&
             sshkey_equal_public(sign_key->cert->signature_key, found_key)) {
-                /* Match of certificate's CA key */
-                if ((r = sshkey_cert_check_authority(sign_key, 0, 1,
-                    principals, &reason)) != 0) {
-                        error("%s:%lu: certificate not authorized: %s",
-                            path, linenum, reason);
+                /* Remove principals listed in file but not allowed by cert */
+                if ((r = cert_filter_principals(path, linenum,
+                    &principals, sign_key)) != 0) {
+                        /* error already displayed */
+                        debug("%s:%lu: cert_filter_principals: %s",
+                            path, linenum, ssh_err(r));
                         goto done;
                 }
                 debug("%s:%lu: matched certificate CA key", path, linenum);
@@ -920,8 +972,8 @@ get_matching_principal_from_line(const char *path, u_long linenum, char *line,
 }
 
 int
-sshsig_find_principal(const char *path, const struct sshkey *sign_key,
-    char **principal)
+sshsig_find_principals(const char *path, const struct sshkey *sign_key,
+    char **principals)
 {
         FILE *f = NULL;
         char *line = NULL;
@@ -939,8 +991,8 @@ sshsig_find_principal(const char *path, const struct sshkey *sign_key,
 
         while (getline(&line, &linesize, f) != -1) {
                 linenum++;
-                r = get_matching_principal_from_line(path, linenum, line,
-                    sign_key, principal);
+                r = get_matching_principals_from_line(path, linenum, line,
+                    sign_key, principals);
                 free(line);
                 line = NULL;
                 if (r == SSH_ERR_KEY_NOT_FOUND)