Allow prepending a list of algorithms to the default set by starting

the list with the '^' character, e.g.

HostKeyAlgorithms ^ssh-ed25519
Ciphers ^aes128-gcm@openssh.com,aes256-gcm@openssh.com

ok djm@ dtucker@

6 files changed, 80 insertions, 19 deletions

diff --git a/usr.bin/ssh/kex.c b/usr.bin/ssh/kex.c
index 7c577361bef..c19052be3d6 100644
--- a/usr.bin/ssh/kex.c
+++ b/usr.bin/ssh/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.153 2019/09/06 01:58:50 djm Exp $ */
+/* $OpenBSD: kex.c,v 1.154 2019/09/06 14:45:34 naddy Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -202,8 +202,9 @@ kex_names_cat(const char *a, const char *b)
 /*
  * Assemble a list of algorithms from a default list and a string from a
  * configuration file. The user-provided string may begin with '+' to
- * indicate that it should be appended to the default or '-' that the
- * specified names should be removed.
+ * indicate that it should be appended to the default, '-' that the
+ * specified names should be removed, or '^' that they should be placed
+ * at the head.
  */
 int
 kex_assemble_names(char **listp, const char *def, const char *all)
@@ -240,6 +241,14 @@ kex_assemble_names(char **listp, const char *def, const char *all)
 		free(list);
 		/* filtering has already been done */
 		return 0;
+	} else if (*list == '^') {
+		/* Place names at head of default list */
+		if ((tmp = kex_names_cat(list + 1, def)) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto fail;
+		}
+		free(list);
+		list = tmp;
 	} else {
 		/* Explicit list, overrides default - just use "list" as is */
 	}
diff --git a/usr.bin/ssh/readconf.c b/usr.bin/ssh/readconf.c
index 4b79e505bf7..5eba1aca3cc 100644
--- a/usr.bin/ssh/readconf.c
+++ b/usr.bin/ssh/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.308 2019/08/09 05:05:54 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.309 2019/09/06 14:45:34 naddy Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1184,7 +1184,8 @@ parse_int:
 		arg = strdelim(&s);
 		if (!arg || *arg == '\0')
 			fatal("%.200s line %d: Missing argument.", filename, linenum);
-		if (*arg != '-' && !ciphers_valid(*arg == '+' ? arg + 1 : arg))
+		if (*arg != '-' &&
+		    !ciphers_valid(*arg == '+' || *arg == '^' ? arg + 1 : arg))
 			fatal("%.200s line %d: Bad SSH2 cipher spec '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && options->ciphers == NULL)
@@ -1195,7 +1196,8 @@ parse_int:
 		arg = strdelim(&s);
 		if (!arg || *arg == '\0')
 			fatal("%.200s line %d: Missing argument.", filename, linenum);
-		if (*arg != '-' && !mac_valid(*arg == '+' ? arg + 1 : arg))
+		if (*arg != '-' &&
+		    !mac_valid(*arg == '+' || *arg == '^' ? arg + 1 : arg))
 			fatal("%.200s line %d: Bad SSH2 MAC spec '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && options->macs == NULL)
@@ -1208,7 +1210,8 @@ parse_int:
 			fatal("%.200s line %d: Missing argument.",
 			    filename, linenum);
 		if (*arg != '-' &&
-		    !kex_names_valid(*arg == '+' ? arg + 1 : arg))
+		    !kex_names_valid(*arg == '+' || *arg == '^' ?
+		    arg + 1 : arg))
 			fatal("%.200s line %d: Bad SSH2 KexAlgorithms '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && options->kex_algorithms == NULL)
@@ -1223,7 +1226,8 @@ parse_keytypes:
 			fatal("%.200s line %d: Missing argument.",
 			    filename, linenum);
 		if (*arg != '-' &&
-		    !sshkey_names_valid2(*arg == '+' ? arg + 1 : arg, 1))
+		    !sshkey_names_valid2(*arg == '+' || *arg == '^' ?
+		    arg + 1 : arg, 1))
 			fatal("%s line %d: Bad key types '%s'.",
 				filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && *charptr == NULL)
diff --git a/usr.bin/ssh/servconf.c b/usr.bin/ssh/servconf.c
index 292db385412..8c64e0e868d 100644
--- a/usr.bin/ssh/servconf.c
+++ b/usr.bin/ssh/servconf.c
@@ -1,5 +1,5 @@
 
-/* $OpenBSD: servconf.c,v 1.351 2019/04/18 18:56:16 dtucker Exp $ */
+/* $OpenBSD: servconf.c,v 1.352 2019/09/06 14:45:34 naddy Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -1381,7 +1381,8 @@ process_server_config_line(ServerOptions *options, char *line,
 			fatal("%s line %d: Missing argument.",
 			    filename, linenum);
 		if (*arg != '-' &&
-		    !sshkey_names_valid2(*arg == '+' ? arg + 1 : arg, 1))
+		    !sshkey_names_valid2(*arg == '+' || *arg == '^' ?
+		    arg + 1 : arg, 1))
 			fatal("%s line %d: Bad key types '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (*activep && *charptr == NULL)
@@ -1652,7 +1653,8 @@ process_server_config_line(ServerOptions *options, char *line,
 		arg = strdelim(&cp);
 		if (!arg || *arg == '\0')
 			fatal("%s line %d: Missing argument.", filename, linenum);
-		if (*arg != '-' && !ciphers_valid(*arg == '+' ? arg + 1 : arg))
+		if (*arg != '-' &&
+		    !ciphers_valid(*arg == '+' || *arg == '^' ? arg + 1 : arg))
 			fatal("%s line %d: Bad SSH2 cipher spec '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (options->ciphers == NULL)
@@ -1663,7 +1665,8 @@ process_server_config_line(ServerOptions *options, char *line,
 		arg = strdelim(&cp);
 		if (!arg || *arg == '\0')
 			fatal("%s line %d: Missing argument.", filename, linenum);
-		if (*arg != '-' && !mac_valid(*arg == '+' ? arg + 1 : arg))
+		if (*arg != '-' &&
+		    !mac_valid(*arg == '+' || *arg == '^' ? arg + 1 : arg))
 			fatal("%s line %d: Bad SSH2 mac spec '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (options->macs == NULL)
@@ -1676,7 +1679,8 @@ process_server_config_line(ServerOptions *options, char *line,
 			fatal("%s line %d: Missing argument.",
 			    filename, linenum);
 		if (*arg != '-' &&
-		    !kex_names_valid(*arg == '+' ? arg + 1 : arg))
+		    !kex_names_valid(*arg == '+' || *arg == '^' ?
+		    arg + 1 : arg))
 			fatal("%s line %d: Bad SSH2 KexAlgorithms '%s'.",
 			    filename, linenum, arg ? arg : "<NONE>");
 		if (options->kex_algorithms == NULL)
diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index d42a76cf067..95f05c59d76 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.505 2019/06/28 13:35:04 deraadt Exp $ */
+/* $OpenBSD: ssh.c,v 1.506 2019/09/06 14:45:34 naddy Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -851,7 +851,7 @@ main(int ac, char **av)
 			}
 			break;
 		case 'c':
-			if (!ciphers_valid(*optarg == '+' ?
+			if (!ciphers_valid(*optarg == '+' || *optarg == '^' ?
 			    optarg + 1 : optarg)) {
 				fprintf(stderr, "Unknown cipher type '%s'\n",
 				    optarg);
diff --git a/usr.bin/ssh/ssh_config.5 b/usr.bin/ssh/ssh_config.5
index 51987b90a93..894e1bea830 100644
--- a/usr.bin/ssh/ssh_config.5
+++ b/usr.bin/ssh/ssh_config.5
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.300 2019/09/04 20:31:15 naddy Exp $
-.Dd $Mdocdate: September 4 2019 $
+.\" $OpenBSD: ssh_config.5,v 1.301 2019/09/06 14:45:34 naddy Exp $
+.Dd $Mdocdate: September 6 2019 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -430,6 +430,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified ciphers (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified ciphers will be placed at the head of the
+default set.
 .Pp
 The supported ciphers are:
 .Bd -literal -offset indent
@@ -794,6 +798,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified key types (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified key types will be placed at the head of the
+default set.
 The default for this option is:
 .Bd -literal -offset 3n
 ecdsa-sha2-nistp256-cert-v01@openssh.com,
@@ -822,6 +830,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified key types (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified key types will be placed at the head of the
+default set.
 The default for this option is:
 .Bd -literal -offset 3n
 ecdsa-sha2-nistp256-cert-v01@openssh.com,
@@ -1052,6 +1064,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified methods (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified methods will be placed at the head of the
+default set.
 The default is:
 .Bd -literal -offset indent
 curve25519-sha256,curve25519-sha256@libssh.org,
@@ -1133,6 +1149,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified algorithms (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified algorithms will be placed at the head of the
+default set.
 .Pp
 The algorithms that contain
 .Qq -etm
@@ -1290,6 +1310,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified key types (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified key types will be placed at the head of the
+default set.
 The default for this option is:
 .Bd -literal -offset 3n
 ecdsa-sha2-nistp256-cert-v01@openssh.com,
diff --git a/usr.bin/ssh/sshd_config.5 b/usr.bin/ssh/sshd_config.5
index 6b8f1566b1a..23cf7000ed2 100644
--- a/usr.bin/ssh/sshd_config.5
+++ b/usr.bin/ssh/sshd_config.5
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: sshd_config.5,v 1.289 2019/09/04 20:31:15 naddy Exp $
-.Dd $Mdocdate: September 4 2019 $
+.\" $OpenBSD: sshd_config.5,v 1.290 2019/09/06 14:45:34 naddy Exp $
+.Dd $Mdocdate: September 6 2019 $
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
@@ -464,6 +464,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified ciphers (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified ciphers will be placed at the head of the
+default set.
 .Pp
 The supported ciphers are:
 .Pp
@@ -678,6 +682,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified key types (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified key types will be placed at the head of the
+default set.
 The default for this option is:
 .Bd -literal -offset 3n
 ecdsa-sha2-nistp256-cert-v01@openssh.com,
@@ -883,6 +891,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified methods (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified methods will be placed at the head of the
+default set.
 The supported algorithms are:
 .Pp
 .Bl -item -compact -offset indent
@@ -1000,6 +1012,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified algorithms (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified algorithms will be placed at the head of the
+default set.
 .Pp
 The algorithms that contain
 .Qq -etm
@@ -1405,6 +1421,10 @@ If the specified list begins with a
 .Sq -
 character, then the specified key types (including wildcards) will be removed
 from the default set instead of replacing them.
+If the specified list begins with a
+.Sq ^
+character, then the specified key types will be placed at the head of the
+default set.
 The default for this option is:
 .Bd -literal -offset 3n
 ecdsa-sha2-nistp256-cert-v01@openssh.com,