upstream commit

When generating all hostkeys (ssh-keygen -A), clobber
existing keys if they exist but are zero length. zero-length keys could
previously be made if ssh-keygen failed part way through generating them, so
avoid that case too. bz#2561 reported by Krzysztof Cieplucha; ok dtucker@

Upstream-ID: f662201c28ab8e1f086b5d43c59cddab5ade4044

1 files changed, 72 insertions, 34 deletions

diff --git a/ssh-keygen.c b/ssh-keygen.c
index d8f942f5a..835f7d016 100644
--- a/ssh-keygen.c
+++ b/ssh-keygen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.306 2017/07/01 13:50:45 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.307 2017/07/07 03:53:12 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -997,20 +997,38 @@ do_gen_all_hostkeys(struct passwd *pw)
         int first = 0;
         struct stat st;
         struct sshkey *private, *public;
-        char comment[1024];
+        char comment[1024], *prv_tmp, *pub_tmp, *prv_file, *pub_file;
         int i, type, fd, r;
         FILE *f;
 
         for (i = 0; key_types[i].key_type; i++) {
-                if (stat(key_types[i].path, &st) == 0)
-                        continue;
-                if (errno != ENOENT) {
+                public = private = NULL;
+                prv_tmp = pub_tmp = prv_file = pub_file = NULL;
+
+                xasprintf(&prv_file, "%s%s",
+                    identity_file, key_types[i].path);
+
+                /* Check whether private key exists and is not zero-length */
+                if (stat(prv_file, &st) == 0) {
+                        if (st.st_size != 0)
+                                goto next;
+                } else if (errno != ENOENT) {
                         error("Could not stat %s: %s", key_types[i].path,
                             strerror(errno));
-                        first = 0;
-                        continue;
+                        goto failnext;
                 }
 
+                /*
+                 * Private key doesn't exist or is invalid; proceed with
+                 * key generation.
+                 */
+                xasprintf(&prv_tmp, "%s%s.XXXXXXXXXX",
+                    identity_file, key_types[i].path);
+                xasprintf(&pub_tmp, "%s%s.pub.XXXXXXXXXX",
+                    identity_file, key_types[i].path);
+                xasprintf(&pub_file, "%s%s.pub",
+                    identity_file, key_types[i].path);
+
                 if (first == 0) {
                         first = 1;
                         printf("%s: generating new host keys: ", __progname);
@@ -1018,56 +1036,76 @@ do_gen_all_hostkeys(struct passwd *pw)
                 printf("%s ", key_types[i].key_type_display);
                 fflush(stdout);
                 type = sshkey_type_from_name(key_types[i].key_type);
-                strlcpy(identity_file, key_types[i].path, sizeof(identity_file));
+                if ((fd = mkstemp(prv_tmp)) == -1) {
+                        error("Could not save your public key in %s: %s",
+                            prv_tmp, strerror(errno));
+                        goto failnext;
+                }
+                close(fd); /* just using mkstemp() to generate/reserve a name */
                 bits = 0;
                 type_bits_valid(type, NULL, &bits);
                 if ((r = sshkey_generate(type, bits, &private)) != 0) {
                         error("sshkey_generate failed: %s", ssh_err(r));
-                        first = 0;
-                        continue;
+                        goto failnext;
                 }
                 if ((r = sshkey_from_private(private, &public)) != 0)
                         fatal("sshkey_from_private failed: %s", ssh_err(r));
                 snprintf(comment, sizeof comment, "%s@%s", pw->pw_name,
                     hostname);
-                if ((r = sshkey_save_private(private, identity_file, "",
+                if ((r = sshkey_save_private(private, prv_tmp, "",
                     comment, use_new_format, new_format_cipher, rounds)) != 0) {
                         error("Saving key \"%s\" failed: %s",
-                            identity_file, ssh_err(r));
-                        sshkey_free(private);
-                        sshkey_free(public);
-                        first = 0;
-                        continue;
+                            prv_tmp, ssh_err(r));
+                        goto failnext;
                 }
-                sshkey_free(private);
-                strlcat(identity_file, ".pub", sizeof(identity_file));
-                fd = open(identity_file, O_WRONLY | O_CREAT | O_TRUNC, 0644);
-                if (fd == -1) {
-                        error("Could not save your public key in %s",
-                            identity_file);
-                        sshkey_free(public);
-                        first = 0;
-                        continue;
+                if ((fd = mkstemp(pub_tmp)) == -1) {
+                        error("Could not save your public key in %s: %s",
+                            pub_tmp, strerror(errno));
+                        goto failnext;
                 }
+                (void)fchmod(fd, 0644);
                 f = fdopen(fd, "w");
                 if (f == NULL) {
-                        error("fdopen %s failed", identity_file);
+                        error("fdopen %s failed: %s", pub_tmp, strerror(errno));
                         close(fd);
-                        sshkey_free(public);
-                        first = 0;
-                        continue;
+                        goto failnext;
                 }
                 if ((r = sshkey_write(public, f)) != 0) {
                         error("write key failed: %s", ssh_err(r));
                         fclose(f);
-                        sshkey_free(public);
-                        first = 0;
-                        continue;
+                        goto failnext;
                 }
                 fprintf(f, " %s\n", comment);
-                fclose(f);
-                sshkey_free(public);
+                if (ferror(f) != 0) {
+                        error("write key failed: %s", strerror(errno));
+                        fclose(f);
+                        goto failnext;
+                }
+                if (fclose(f) != 0) {
+                        error("key close failed: %s", strerror(errno));
+                        goto failnext;
+                }
 
+                /* Rename temporary files to their permanent locations. */
+                if (rename(pub_tmp, pub_file) != 0) {
+                        error("Unable to move %s into position: %s",
+                            pub_file, strerror(errno));
+                        goto failnext;
+                }
+                if (rename(prv_tmp, prv_file) != 0) {
+                        error("Unable to move %s into position: %s",
+                            key_types[i].path, strerror(errno));
+ failnext:
+                        first = 0;
+                        goto next;
+                }
+ next:
+                sshkey_free(private);
+                sshkey_free(public);
+                free(prv_tmp);
+                free(pub_tmp);
+                free(prv_file);
+                free(pub_file);
         }
         if (first != 0)
                 printf("\n");