9 files changed, 220 insertions, 31 deletions

diff --git a/Makefile.in b/Makefile.in
index 2486edc95..1f78ea9cc 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,4 +1,4 @@
-# $Id: Makefile.in,v 1.285 2007/06/11 04:01:42 djm Exp $
+# $Id: Makefile.in,v 1.286 2008/02/10 11:40:12 djm Exp $
 
 # uncomment if you run a non bourne compatable shell. Ie. csh
 #SHELL = @SH@
@@ -156,8 +156,8 @@ ssh-keysign$(EXEEXT): $(LIBCOMPAT) libssh.a ssh-keysign.o
 ssh-keyscan$(EXEEXT): $(LIBCOMPAT) libssh.a ssh-keyscan.o
         $(LD) -o $@ ssh-keyscan.o $(LDFLAGS) -lssh -lopenbsd-compat -lssh $(LIBS)
 
-sftp-server$(EXEEXT): $(LIBCOMPAT) libssh.a sftp.o sftp-common.o sftp-server.o
-        $(LD) -o $@ sftp-server.o sftp-common.o $(LDFLAGS) -lssh -lopenbsd-compat $(LIBS)
+sftp-server$(EXEEXT): $(LIBCOMPAT) libssh.a sftp.o sftp-common.o sftp-server.o sftp-server-main.o
+        $(LD) -o $@ sftp-server.o sftp-common.o sftp-server-main.o $(LDFLAGS) -lssh -lopenbsd-compat $(LIBS)
 
 sftp$(EXEEXT): $(LIBCOMPAT) libssh.a sftp.o sftp-client.o sftp-common.o sftp-glob.o progressmeter.o
         $(LD) -o $@ progressmeter.o sftp.o sftp-client.o sftp-common.o sftp-glob.o $(LDFLAGS) -lssh -lopenbsd-compat $(LIBS) $(LIBEDIT)
diff --git a/servconf.c b/servconf.c
index 19c286c18..d38d0bfb1 100644
--- a/servconf.c
+++ b/servconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.c,v 1.175 2008/01/01 09:27:33 dtucker Exp $ */
+/* $OpenBSD: servconf.c,v 1.176 2008/02/08 23:24:08 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -122,6 +122,7 @@ initialize_server_options(ServerOptions *options)
         options->permit_tun = -1;
         options->num_permitted_opens = -1;
         options->adm_forced_command = NULL;
+        options->chroot_directory = NULL;
 }
 
 void
@@ -291,7 +292,7 @@ typedef enum {
         sHostbasedUsesNameFromPacketOnly, sClientAliveInterval,
         sClientAliveCountMax, sAuthorizedKeysFile, sAuthorizedKeysFile2,
         sGssAuthentication, sGssCleanupCreds, sAcceptEnv, sPermitTunnel,
-        sMatch, sPermitOpen, sForceCommand,
+        sMatch, sPermitOpen, sForceCommand, sChrootDirectory,
         sUsePrivilegeSeparation,
         sDeprecated, sUnsupported
 } ServerOpCodes;
@@ -403,6 +404,7 @@ static struct {
         { "match", sMatch, SSHCFG_ALL },
         { "permitopen", sPermitOpen, SSHCFG_ALL },
         { "forcecommand", sForceCommand, SSHCFG_ALL },
+        { "chrootdirectory", sChrootDirectory, SSHCFG_ALL },
         { NULL, sBadOption, 0 }
 };
 
@@ -1147,6 +1149,7 @@ parse_flag:
         case sBanner:
                 charptr = &options->banner;
                 goto parse_filename;
+
         /*
          * These options can contain %X options expanded at
          * connect time, so that you can specify paths like:
@@ -1255,6 +1258,10 @@ parse_flag:
                         options->adm_forced_command = xstrdup(cp + len);
                 return 0;
 
+        case sChrootDirectory:
+                charptr = &options->chroot_directory;
+                goto parse_filename;
+
         case sDeprecated:
                 logit("%s line %d: Deprecated option %s",
                     filename, linenum, arg);
@@ -1363,6 +1370,7 @@ copy_set_server_options(ServerOptions *dst, ServerOptions *src, int preauth)
         if (preauth)
                 return;
         M_CP_STROPT(adm_forced_command);
+        M_CP_STROPT(chroot_directory);
 }
 
 #undef M_CP_INTOPT
diff --git a/servconf.h b/servconf.h
index 8a5b950ea..81a68be89 100644
--- a/servconf.h
+++ b/servconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.h,v 1.80 2007/02/19 10:45:58 dtucker Exp $ */
+/* $OpenBSD: servconf.h,v 1.81 2008/02/08 23:24:08 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -141,6 +141,8 @@ typedef struct {
         int     permit_tun;
 
         int     num_permitted_opens;
+
+        char   *chroot_directory;
 }       ServerOptions;
 
 void     initialize_server_options(ServerOptions *);
diff --git a/session.c b/session.c
index a1319b384..1768c8c2f 100644
--- a/session.c
+++ b/session.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: session.c,v 1.225 2008/02/04 21:53:00 markus Exp $ */
+/* $OpenBSD: session.c,v 1.226 2008/02/08 23:24:07 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -84,6 +84,7 @@
 #include "sshlogin.h"
 #include "serverloop.h"
 #include "canohost.h"
+#include "misc.h"
 #include "session.h"
 #include "kex.h"
 #include "monitor_wrap.h"
@@ -93,6 +94,9 @@
 #include <kafs.h>
 #endif
 
+/* Magic name for internal sftp-server */
+#define INTERNAL_SFTP_NAME      "internal-sftp"
+
 /* func */
 
 Session *session_new(void);
@@ -130,7 +134,7 @@ extern Buffer loginmsg;
 const char *original_command = NULL;
 
 /* data */
-#define MAX_SESSIONS 10
+#define MAX_SESSIONS 20
 Session sessions[MAX_SESSIONS];
 
 #define SUBSYSTEM_NONE          0
@@ -688,13 +692,17 @@ do_exec(Session *s, const char *command)
         if (options.adm_forced_command) {
                 original_command = command;
                 command = options.adm_forced_command;
-                if (s->is_subsystem)
+                if (strcmp(INTERNAL_SFTP_NAME, command) == 0)
+                        s->is_subsystem = SUBSYSTEM_INT_SFTP;
+                else if (s->is_subsystem)
                         s->is_subsystem = SUBSYSTEM_EXT;
                 debug("Forced command (config) '%.900s'", command);
         } else if (forced_command) {
                 original_command = command;
                 command = forced_command;
-                if (s->is_subsystem)
+                if (strcmp(INTERNAL_SFTP_NAME, command) == 0)
+                        s->is_subsystem = SUBSYSTEM_INT_SFTP;
+                else if (s->is_subsystem)
                         s->is_subsystem = SUBSYSTEM_EXT;
                 debug("Forced command (key option) '%.900s'", command);
         }
@@ -710,7 +718,6 @@ do_exec(Session *s, const char *command)
                 PRIVSEP(audit_run_command(shell));
         }
 #endif
-
         if (s->ttyfd != -1)
                 do_exec_pty(s, command);
         else
@@ -1293,6 +1300,61 @@ do_nologin(struct passwd *pw)
         }
 }
 
+/*
+ * Chroot into a directory after checking it for safety: all path components
+ * must be root-owned directories with strict permissions.
+ */
+static void
+safely_chroot(const char *path, uid_t uid)
+{
+        const char *cp;
+        char component[MAXPATHLEN];
+        struct stat st;
+
+        if (*path != '/')
+                fatal("chroot path does not begin at root");
+        if (strlen(path) >= sizeof(component))
+                fatal("chroot path too long");
+
+        /*
+         * Descend the path, checking that each component is a
+         * root-owned directory with strict permissions.
+         */
+        for (cp = path; cp != NULL;) {
+                if ((cp = strchr(cp, '/')) == NULL)
+                        strlcpy(component, path, sizeof(component));
+                else {
+                        cp++;
+                        memcpy(component, path, cp - path);
+                        component[cp - path] = '\0';
+                }
+        
+                debug3("%s: checking '%s'", __func__, component);
+
+                if (stat(component, &st) != 0)
+                        fatal("%s: stat(\"%s\"): %s", __func__,
+                            component, strerror(errno));
+                if (st.st_uid != 0 || (st.st_mode & 022) != 0)
+                        fatal("bad ownership or modes for chroot "
+                            "directory %s\"%s\"", 
+                            cp == NULL ? "" : "component ", component);
+                if (!S_ISDIR(st.st_mode))
+                        fatal("chroot path %s\"%s\" is not a directory",
+                            cp == NULL ? "" : "component ", component);
+
+        }
+
+        if (chdir(path) == -1)
+                fatal("Unable to chdir to chroot path \"%s\": "
+                    "%s", path, strerror(errno));
+        if (chroot(path) == -1)
+                fatal("chroot(\"%s\"): %s", path, strerror(errno));
+        if (chdir("/") == -1)
+                fatal("%s: chdir(/) after chroot: %s",
+                    __func__, strerror(errno));
+        verbose("Changed root directory to \"%s\"", path);
+}
+
 /* Set login name, uid, gid, and groups. */
 void
 do_setusercontext(struct passwd *pw)
@@ -1324,7 +1386,7 @@ do_setusercontext(struct passwd *pw)
                 }
 # endif /* USE_PAM */
                 if (setusercontext(lc, pw, pw->pw_uid,
-                    (LOGIN_SETALL & ~LOGIN_SETPATH)) < 0) {
+                    (LOGIN_SETALL & ~(LOGIN_SETPATH|LOGIN_SETUSER))) < 0) {
                         perror("unable to set user context");
                         exit(1);
                 }
@@ -1347,13 +1409,13 @@ do_setusercontext(struct passwd *pw)
                         exit(1);
                 }
                 endgrent();
-#ifdef GSSAPI
+# ifdef GSSAPI
                 if (options.gss_authentication) {
                         temporarily_use_uid(pw);
                         ssh_gssapi_storecreds();
                         restore_uid();
                 }
-#endif
+# endif
 # ifdef USE_PAM
                 /*
                  * PAM credentials may take the form of supplementary groups.
@@ -1367,15 +1429,33 @@ do_setusercontext(struct passwd *pw)
 # endif /* USE_PAM */
 # if defined(WITH_IRIX_PROJECT) || defined(WITH_IRIX_JOBS) || defined(WITH_IRIX_ARRAY)
                 irix_setusercontext(pw);
-#  endif /* defined(WITH_IRIX_PROJECT) || defined(WITH_IRIX_JOBS) || defined(WITH_IRIX_ARRAY) */
+# endif /* defined(WITH_IRIX_PROJECT) || defined(WITH_IRIX_JOBS) || defined(WITH_IRIX_ARRAY) */
 # ifdef _AIX
                 aix_usrinfo(pw);
 # endif /* _AIX */
-#ifdef USE_LIBIAF
+# ifdef USE_LIBIAF
                 if (set_id(pw->pw_name) != 0) {
                         exit(1);
                 }
-#endif /* USE_LIBIAF */
+# endif /* USE_LIBIAF */
+#endif
+
+                if (options.chroot_directory != NULL &&
+                    strcasecmp(options.chroot_directory, "none") != 0) {
+                        char *chroot_path;
+
+                        chroot_path = percent_expand(options.chroot_directory,
+                            "h", pw->pw_dir, "u", pw->pw_name, (char *)NULL);
+                        safely_chroot(chroot_path, pw->pw_uid);
+                        free(chroot_path);
+                }
+
+#ifdef HAVE_LOGIN_CAP
+                if (setusercontext(lc, pw, pw->pw_uid, LOGIN_SETUSER) < 0) {
+                        perror("unable to set user context (setuser)");
+                        exit(1);
+                }
+#else
                 /* Permanently switch to the desired uid. */
                 permanently_set_uid(pw);
 #endif
@@ -1625,7 +1705,7 @@ do_child(Session *s, const char *command)
                 argv[i] = NULL;
                 optind = optreset = 1;
                 __progname = argv[0];
-                exit(sftp_server_main(i, argv));
+                exit(sftp_server_main(i, argv, s->pw));
         }
 
         if (options.use_login) {
@@ -1900,7 +1980,7 @@ session_subsystem_req(Session *s)
                 if (strcmp(subsys, options.subsystem_name[i]) == 0) {
                         prog = options.subsystem_command[i];
                         cmd = options.subsystem_args[i];
-                        if (!strcmp("internal-sftp", prog)) {
+                        if (!strcmp(INTERNAL_SFTP_NAME, prog)) {
                                 s->is_subsystem = SUBSYSTEM_INT_SFTP;
                         } else if (stat(prog, &st) < 0) {
                                 error("subsystem: cannot stat %s: %s", prog,
diff --git a/sftp-server-main.c b/sftp-server-main.c
new file mode 100644
index 000000000..1d2ea6220
--- /dev/null
+++ b/sftp-server-main.c
@@ -0,0 +1,50 @@
+/* $OpenBSD: */
+/*
+ * Copyright (c) 2008 Markus Friedl.  All rights reserved.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+#include <pwd.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "log.h"
+#include "sftp.h"
+#include "misc.h"
+
+void
+cleanup_exit(int i)
+{
+        sftp_server_cleanup_exit(i);
+}
+
+int
+main(int argc, char **argv)
+{
+        struct passwd *user_pw;
+
+        /* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
+        sanitise_stdfd();
+
+        if ((user_pw = getpwuid(getuid())) == NULL) {
+                fprintf(stderr, "No user found for uid %lu", (u_long)getuid());
+                return 1;
+        }
+
+        return (sftp_server_main(argc, argv, user_pw));
+}
diff --git a/sftp-server.c b/sftp-server.c
index 373bd5eda..44ccefff8 100644
--- a/sftp-server.c
+++ b/sftp-server.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sftp-server.c,v 1.76 2008/02/04 21:53:00 markus Exp $ */
+/* $OpenBSD: sftp-server.c,v 1.77 2008/02/08 23:24:07 djm Exp $ */
 /*
  * Copyright (c) 2000-2004 Markus Friedl.  All rights reserved.
  *
@@ -1219,7 +1219,7 @@ sftp_server_usage(void)
 }
 
 int
-sftp_server_main(int argc, char **argv)
+sftp_server_main(int argc, char **argv, struct passwd *user_pw)
 {
         fd_set *rset, *wset;
         int in, out, max, ch, skipargs = 0, log_stderr = 0;
@@ -1277,11 +1277,7 @@ sftp_server_main(int argc, char **argv)
         } else
                 client_addr = xstrdup("UNKNOWN");
 
-        if ((pw = getpwuid(getuid())) == NULL) {
-                error("No user found for uid %lu", (u_long)getuid());
-                sftp_server_cleanup_exit(255);
-        }
-        pw = pwcopy(pw);
+        pw = pwcopy(user_pw);
 
         logit("session opened for local user %s from [%s]",
             pw->pw_name, client_addr);
diff --git a/sftp.h b/sftp.h
index 12b9cc056..0835da6ed 100644
--- a/sftp.h
+++ b/sftp.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sftp.h,v 1.6 2008/02/04 21:53:00 markus Exp $ */
+/* $OpenBSD: sftp.h,v 1.7 2008/02/08 23:24:07 djm Exp $ */
 
 /*
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -91,5 +91,7 @@
 #define SSH2_FX_OP_UNSUPPORTED          8
 #define SSH2_FX_MAX                     8
 
-int     sftp_server_main(int, char **);
+struct passwd;
+
+int     sftp_server_main(int, char **, struct passwd *);
 void    sftp_server_cleanup_exit(int) __dead;
diff --git a/sshd_config b/sshd_config
index c7094e775..ddfbbe91e 100644
--- a/sshd_config
+++ b/sshd_config
@@ -1,4 +1,4 @@
-#       $OpenBSD: sshd_config,v 1.76 2007/08/23 03:22:16 djm Exp $
+#       $OpenBSD: sshd_config,v 1.77 2008/02/08 23:24:07 djm Exp $
 
 # This is the sshd server system-wide configuration file.  See
 # sshd_config(5) for more information.
@@ -102,6 +102,7 @@ Protocol 2
 #PidFile /var/run/sshd.pid
 #MaxStartups 10
 #PermitTunnel no
+#ChrootDirectory none
 
 # no default banner path
 #Banner none
diff --git a/sshd_config.5 b/sshd_config.5
index aa6720dc3..2f83bf2e1 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -34,8 +34,8 @@
 .\" (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 1.79 2008/01/01 09:27:33 dtucker Exp $
-.Dd $Mdocdate: January 1 2008 $
+.\" $OpenBSD: sshd_config.5,v 1.80 2008/02/08 23:24:07 djm Exp $
+.Dd $Mdocdate: February 8 2008 $
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
@@ -173,6 +173,45 @@ All authentication styles from
 are supported.
 The default is
 .Dq yes .
+.It Cm ChrootDirectory
+Specifies a path to
+.Xr chroot 2
+to after authentication.
+This path, and all its components, must be root-owned directories that are
+not writable by any other user or group.
+.Pp
+The path may contain the following tokens that are expanded at runtime once
+the connecting user has been authenticated: %% is replaced by a literal '%',
+%h is replaced by the home directory of the user being authenticated, and
+%u is replaced by the username of that user.
+.Pp
+The
+.Cm ChrootDirectory
+must contain the necessary files and directories to support the
+users' session.
+For an interactive session this requires at least a shell, typically
+.Xr sh 1 ,
+and basic
+.Pa /dev
+nodes such as
+.Xr null 4 ,
+.Xr zero 4 ,
+.Xr stdin 4 ,
+.Xr stdout 4 ,
+.Xr stderr 4 ,
+.Xr arandom 4
+and
+.Xr tty 4
+devices.
+For file transfer sessions using
+.Dq sftp ,
+no additional configuration of the environment is necessary if the
+in-process sftp server is used (see
+.Cm Subsystem
+for details.
+.Pp
+The default is not to
+.Xr chroot 2 .
 .It Cm Ciphers
 Specifies the ciphers allowed for protocol version 2.
 Multiple ciphers must be comma-separated.
@@ -740,11 +779,22 @@ The default is
 Configures an external subsystem (e.g. file transfer daemon).
 Arguments should be a subsystem name and a command (with optional arguments)
 to execute upon subsystem request.
+.Pp
 The command
 .Xr sftp-server 8
 implements the
 .Dq sftp
 file transfer subsystem.
+.Pp
+Alternately the name
+.Dq internal-sftp
+implements an in-process
+.Dq sftp
+server.
+This may simplify configurations using
+.Cm ChrootDirectory
+to force a different filesystem root on clients.
+.Pp
 By default no subsystems are defined.
 Note that this option applies to protocol version 2 only.
 .It Cm SyslogFacility