backdoor by authorized_keys2 leftovers
Damien Miller
djm at mindrot.org
Mon May 16 13:14:15 EST 2011
On Mon, 16 May 2011, Damien Miller wrote:
> On Sun, 15 May 2011, Daniel Kahn Gillmor wrote:
>
> > It seems somewhat unclear how AuthorizedKeysFile interacts with a Match
> > clause.
> >
> > If the following makes an array of two authorizedkeysfiles:
> >
> > AuthorizedKeysFile foo
> > AuthorizedKeysFile bar
>
> So the question is whether to allow multiple directives that add to the
> list (as is the case in the slightly-broken patch I sent out yesterday)
> or to allow a single directive that specifies all the files on one line.
>
> The latter is more clear for Match, but long lines are more likely to wrap
> and are harder to read in sshd_config.
>
> That being said, there is plenty of room for the common cases that I can
> think of:
>
> AuthorizedKeysFile .ssh/authorized_keys
> AuthorizedKeysFile .ssh/authorized_keys .ssh/authorized_keys2
> AuthorizedKeysFile /etc/ssh/authorized_keys/keys_%u .ssh/authorized_keys
>
> So maybe all-keys-on-one-line is better.
Here's a diff that implements this:
Index: auth-rsa.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/auth-rsa.c,v
retrieving revision 1.79
diff -u -p -r1.79 auth-rsa.c
--- auth-rsa.c 3 Dec 2010 23:55:27 -0000 1.79
+++ auth-rsa.c 16 May 2011 03:12:58 -0000
@@ -157,44 +157,27 @@ auth_rsa_challenge_dialog(Key *key)
return (success);
}
-/*
- * check if there's user key matching client_n,
- * return key if login is allowed, NULL otherwise
- */
-
-int
-auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
+static int
+rsa_key_allowed_in_file(struct passwd *pw, char *file,
+ const BIGNUM *client_n, Key **rkey)
{
- char line[SSH_MAX_PUBKEY_BYTES], *file;
+ char line[SSH_MAX_PUBKEY_BYTES];
int allowed = 0;
u_int bits;
FILE *f;
u_long linenum = 0;
Key *key;
- /* Temporarily use the user's uid. */
- temporarily_use_uid(pw);
-
- /* The authorized keys. */
- file = authorized_keys_file(pw);
debug("trying public RSA key file %s", file);
- f = auth_openkeyfile(file, pw, options.strict_modes);
- if (!f) {
- xfree(file);
- restore_uid();
- return (0);
- }
-
- /* Flag indicating whether the key is allowed. */
- allowed = 0;
-
- key = key_new(KEY_RSA1);
+ if ((f = auth_openkeyfile(file, pw, options.strict_modes)) == NULL)
+ return 0;
/*
* Go though the accepted keys, looking for the current key. If
* found, perform a challenge-response dialog to verify that the
* user really has the corresponding private key.
*/
+ key = key_new(KEY_RSA1);
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
char *cp;
char *key_options;
@@ -232,7 +215,10 @@ auth_rsa_key_allowed(struct passwd *pw,
}
/* cp now points to the comment part. */
- /* Check if the we have found the desired key (identified by its modulus). */
+ /*
+ * Check if the we have found the desired key (identified
+ * by its modulus).
+ */
if (BN_cmp(key->rsa->n, client_n) != 0)
continue;
@@ -261,11 +247,7 @@ auth_rsa_key_allowed(struct passwd *pw,
break;
}
- /* Restore the privileged uid. */
- restore_uid();
-
/* Close the file. */
- xfree(file);
fclose(f);
/* return key if allowed */
@@ -273,7 +255,33 @@ auth_rsa_key_allowed(struct passwd *pw,
*rkey = key;
else
key_free(key);
- return (allowed);
+
+ return allowed;
+}
+
+/*
+ * check if there's user key matching client_n,
+ * return key if login is allowed, NULL otherwise
+ */
+
+int
+auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
+{
+ char *file;
+ u_int i, allowed = 0;
+
+ temporarily_use_uid(pw);
+
+ for (i = 0; !allowed && i < options.num_authkeys_files; i++) {
+ file = expand_authorized_keys(
+ options.authorized_keys_files[i], pw);
+ allowed = rsa_key_allowed_in_file(pw, file, client_n, rkey);
+ xfree(file);
+ }
+
+ restore_uid();
+
+ return allowed;
}
/*
Index: auth.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/auth.c,v
retrieving revision 1.92
diff -u -p -r1.92 auth.c
--- auth.c 11 May 2011 04:47:06 -0000 1.92
+++ auth.c 16 May 2011 03:12:58 -0000
@@ -241,7 +241,7 @@ auth_root_allowed(char *method)
*
* This returns a buffer allocated by xmalloc.
*/
-static char *
+char *
expand_authorized_keys(const char *filename, struct passwd *pw)
{
char *file, ret[MAXPATHLEN];
@@ -262,12 +262,6 @@ expand_authorized_keys(const char *filen
fatal("expand_authorized_keys: path too long");
xfree(file);
return (xstrdup(ret));
-}
-
-char *
-authorized_keys_file(struct passwd *pw)
-{
- return expand_authorized_keys(options.authorized_keys_file, pw);
}
char *
Index: auth.h
===================================================================
RCS file: /cvs/src/usr.bin/ssh/auth.h,v
retrieving revision 1.68
diff -u -p -r1.68 auth.h
--- auth.h 11 May 2011 04:47:06 -0000 1.68
+++ auth.h 16 May 2011 03:12:58 -0000
@@ -145,7 +145,7 @@ struct passwd * getpwnamallow(const char
char *get_challenge(Authctxt *);
int verify_response(Authctxt *, const char *);
-char *authorized_keys_file(struct passwd *);
+char *expand_authorized_keys(const char *, struct passwd *pw);
char *authorized_principals_file(struct passwd *);
FILE *auth_openkeyfile(const char *, struct passwd *, int);
Index: auth2-pubkey.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/auth2-pubkey.c,v
retrieving revision 1.28
diff -u -p -r1.28 auth2-pubkey.c
--- auth2-pubkey.c 11 May 2011 04:47:06 -0000 1.28
+++ auth2-pubkey.c 16 May 2011 03:12:58 -0000
@@ -435,7 +435,7 @@ user_cert_trusted_ca(struct passwd *pw,
int
user_key_allowed(struct passwd *pw, Key *key)
{
- int success;
+ u_int success, i;
char *file;
if (auth_key_is_revoked(key))
@@ -447,9 +447,12 @@ user_key_allowed(struct passwd *pw, Key
if (success)
return success;
- file = authorized_keys_file(pw);
- success = user_key_allowed2(pw, key, file);
- xfree(file);
+ for (i = 0; !success && i < options.num_authkeys_files; i++) {
+ file = expand_authorized_keys(
+ options.authorized_keys_files[i], pw);
+ success = user_key_allowed2(pw, key, file);
+ xfree(file);
+ }
return success;
}
Index: pathnames.h
===================================================================
RCS file: /cvs/src/usr.bin/ssh/pathnames.h,v
retrieving revision 1.21
diff -u -p -r1.21 pathnames.h
--- pathnames.h 11 May 2011 04:47:06 -0000 1.21
+++ pathnames.h 16 May 2011 03:12:58 -0000
@@ -88,6 +88,9 @@
*/
#define _PATH_SSH_USER_PERMITTED_KEYS ".ssh/authorized_keys"
+/* backward compat for protocol v2 */
+#define _PATH_SSH_USER_PERMITTED_KEYS2 ".ssh/authorized_keys2"
+
/*
* Per-user and system-wide ssh "rc" files. These files are executed with
* /bin/sh before starting the shell or command if they exist. They will be
Index: servconf.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/servconf.c,v
retrieving revision 1.215
diff -u -p -r1.215 servconf.c
--- servconf.c 11 May 2011 04:47:06 -0000 1.215
+++ servconf.c 16 May 2011 03:12:58 -0000
@@ -119,7 +119,7 @@ initialize_server_options(ServerOptions
options->use_dns = -1;
options->client_alive_interval = -1;
options->client_alive_count_max = -1;
- options->authorized_keys_file = NULL;
+ options->num_authkeys_files = 0;
options->num_accept_env = 0;
options->permit_tun = -1;
options->num_permitted_opens = -1;
@@ -249,8 +249,12 @@ fill_default_server_options(ServerOption
options->client_alive_interval = 0;
if (options->client_alive_count_max == -1)
options->client_alive_count_max = 3;
- if (options->authorized_keys_file == NULL)
- options->authorized_keys_file = xstrdup(_PATH_SSH_USER_PERMITTED_KEYS);
+ if (options->num_authkeys_files == 0) {
+ options->authorized_keys_files[options->num_authkeys_files++] =
+ xstrdup(_PATH_SSH_USER_PERMITTED_KEYS);
+ options->authorized_keys_files[options->num_authkeys_files++] =
+ xstrdup(_PATH_SSH_USER_PERMITTED_KEYS2);
+ }
if (options->permit_tun == -1)
options->permit_tun = SSH_TUNMODE_NO;
if (options->zero_knowledge_password_authentication == -1)
@@ -286,7 +290,7 @@ typedef enum {
sMaxStartups, sMaxAuthTries, sMaxSessions,
sBanner, sUseDNS, sHostbasedAuthentication,
sHostbasedUsesNameFromPacketOnly, sClientAliveInterval,
- sClientAliveCountMax, sAuthorizedKeysFile, sAuthorizedKeysFile2,
+ sClientAliveCountMax, sAuthorizedKeysFile,
sGssAuthentication, sGssCleanupCreds, sAcceptEnv, sPermitTunnel,
sMatch, sPermitOpen, sForceCommand, sChrootDirectory,
sUsePrivilegeSeparation, sAllowAgentForwarding,
@@ -391,7 +395,6 @@ static struct {
{ "clientaliveinterval", sClientAliveInterval, SSHCFG_GLOBAL },
{ "clientalivecountmax", sClientAliveCountMax, SSHCFG_GLOBAL },
{ "authorizedkeysfile", sAuthorizedKeysFile, SSHCFG_ALL },
- { "authorizedkeysfile2", sAuthorizedKeysFile2, SSHCFG_ALL },
{ "useprivilegeseparation", sUsePrivilegeSeparation, SSHCFG_GLOBAL},
{ "acceptenv", sAcceptEnv, SSHCFG_GLOBAL },
{ "permittunnel", sPermitTunnel, SSHCFG_ALL },
@@ -1197,11 +1200,22 @@ process_server_config_line(ServerOptions
* AuthorizedKeysFile /etc/ssh_keys/%u
*/
case sAuthorizedKeysFile:
- charptr = &options->authorized_keys_file;
- goto parse_tilde_filename;
+ if (*activep && options->num_authkeys_files == 0) {
+ while ((arg = strdelim(&cp)) && *arg != '\0') {
+ if (options->num_authkeys_files >=
+ MAX_AUTHKEYS_FILES)
+ fatal("%s line %d: "
+ "too many authorized keys files.",
+ filename, linenum);
+ options->authorized_keys_files[
+ options->num_authkeys_files++] =
+ tilde_expand_filename(arg, getuid());
+ }
+ }
+ return 0;
+
case sAuthorizedPrincipalsFile:
charptr = &options->authorized_principals_file;
- parse_tilde_filename:
arg = strdelim(&cp);
if (!arg || *arg == '\0')
fatal("%s line %d: missing file name.",
@@ -1420,6 +1434,12 @@ parse_server_match_config(ServerOptions
dst->n = src->n; \
} \
} while(0)
+#define M_CP_STRARRAYOPT(n, num_n) do {\
+ if (src->num_n != 0) { \
+ for (dst->num_n = 0; dst->num_n < src->num_n; dst->num_n++) \
+ dst->n[dst->num_n] = xstrdup(src->n[dst->num_n]); \
+ } \
+} while(0)
/*
* Copy any supported values that are set.
@@ -1455,19 +1475,23 @@ copy_set_server_options(ServerOptions *d
M_CP_INTOPT(ip_qos_interactive);
M_CP_INTOPT(ip_qos_bulk);
+ M_CP_STROPT(authorized_principals_file);
M_CP_STROPT(banner);
+ M_CP_STROPT(revoked_keys_file);
+ M_CP_STROPT(trusted_user_ca_keys);
+
+ M_CP_STRARRAYOPT(authorized_keys_files, num_authkeys_files);
+
if (preauth)
return;
+
M_CP_STROPT(adm_forced_command);
M_CP_STROPT(chroot_directory);
- M_CP_STROPT(trusted_user_ca_keys);
- M_CP_STROPT(revoked_keys_file);
- M_CP_STROPT(authorized_keys_file);
- M_CP_STROPT(authorized_principals_file);
}
#undef M_CP_INTOPT
#undef M_CP_STROPT
+#undef M_CP_STRARRAYOPT
void
parse_server_config(ServerOptions *options, const char *filename, Buffer *conf,
@@ -1674,7 +1698,6 @@ dump_config(ServerOptions *o)
dump_cfg_string(sCiphers, o->ciphers);
dump_cfg_string(sMacs, o->macs);
dump_cfg_string(sBanner, o->banner);
- dump_cfg_string(sAuthorizedKeysFile, o->authorized_keys_file);
dump_cfg_string(sForceCommand, o->adm_forced_command);
dump_cfg_string(sChrootDirectory, o->chroot_directory);
dump_cfg_string(sTrustedUserCAKeys, o->trusted_user_ca_keys);
@@ -1687,6 +1710,8 @@ dump_config(ServerOptions *o)
dump_cfg_string(sLogFacility, log_facility_name(o->log_facility));
/* string array arguments */
+ dump_cfg_strarray(sAuthorizedKeysFile, o->num_authkeys_files,
+ o->authorized_keys_files);
dump_cfg_strarray(sHostKeyFile, o->num_host_key_files,
o->host_key_files);
dump_cfg_strarray(sHostKeyFile, o->num_host_cert_files,
Index: servconf.h
===================================================================
RCS file: /cvs/src/usr.bin/ssh/servconf.h,v
retrieving revision 1.96
diff -u -p -r1.96 servconf.h
--- servconf.h 11 May 2011 04:47:06 -0000 1.96
+++ servconf.h 16 May 2011 03:12:58 -0000
@@ -27,6 +27,7 @@
#define MAX_HOSTCERTS 256 /* Max # host certificates. */
#define MAX_ACCEPT_ENV 256 /* Max # of env vars. */
#define MAX_MATCH_GROUPS 256 /* Max # of groups for Match. */
+#define MAX_AUTHKEYS_FILES 256 /* Max # of authorized_keys files. */
/* permit_root_login */
#define PERMIT_NOT_SET -1
@@ -145,7 +146,8 @@ typedef struct {
* disconnect the session
*/
- char *authorized_keys_file; /* File containing public keys */
+ u_int num_authkeys_files; /* Files containing public keys */
+ char *authorized_keys_files[MAX_AUTHKEYS_FILES];
char *adm_forced_command;
Index: sshd.8
===================================================================
RCS file: /cvs/src/usr.bin/ssh/sshd.8,v
retrieving revision 1.260
diff -u -p -r1.260 sshd.8
--- sshd.8 28 Oct 2010 18:33:28 -0000 1.260
+++ sshd.8 16 May 2011 03:12:59 -0000
@@ -435,10 +435,12 @@ is run, and if that
does not exist either, xauth is used to add the cookie.
.Sh AUTHORIZED_KEYS FILE FORMAT
.Cm AuthorizedKeysFile
-specifies the file containing public keys for
+specifies the file or files containing public keys for
public key authentication;
-if none is specified, the default is
-.Pa ~/.ssh/authorized_keys .
+if none is specified, the default is both
+.Pa ~/.ssh/authorized_keys
+and
+.Pa ~/.ssh/authorized_keys2 .
Each line of the file contains one
key (empty lines and lines starting with a
.Ql #
Index: sshd_config.5
===================================================================
RCS file: /cvs/src/usr.bin/ssh/sshd_config.5,v
retrieving revision 1.131
diff -u -p -r1.131 sshd_config.5
--- sshd_config.5 8 Dec 2010 04:02:47 -0000 1.131
+++ sshd_config.5 16 May 2011 03:12:59 -0000
@@ -168,8 +168,14 @@ After expansion,
.Cm AuthorizedKeysFile
is taken to be an absolute path or one relative to the user's home
directory.
-The default is
-.Dq .ssh/authorized_keys .
+The default is both
+.Dq .ssh/authorized_keys
+and
+.Dq .ssh/authorized_keys2 .
+Multiple files may be listed, either on a single line separated by
+whitespace or on additional
+.Cm AuthorizedKeysFile
+lines.
.It Cm AuthorizedPrincipalsFile
Specifies a file that lists principal names that are accepted for
certificate authentication.
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