openssh/openssh-6.6p1-sftp_homechroot.patch

# run sftp sessions inside a chroot

Index: b/session.c
===================================================================
--- a/session.c
+++ b/session.c
@@ -127,6 +127,8 @@ void	do_child(Session *, const char *);
 void	do_motd(void);
 int	check_quietlogin(Session *, const char *);
 
+int	chroot_no_tree = 0;
+
 static void do_authenticated1(Authctxt *);
 static void do_authenticated2(Authctxt *);
 
@@ -816,6 +818,11 @@ do_exec(Session *s, const char *command)
 		snprintf(session_type, sizeof(session_type), "command");
 	}
 
+	if ((s->is_subsystem != SUBSYSTEM_INT_SFTP) && chroot_no_tree) {
+		logit("You aren't welcomed, go away!");
+		exit (1);
+	}
+
 	if (s->ttyfd != -1) {
 		tty = s->tty;
 		if (strncmp(tty, "/dev/", 5) == 0)
@@ -1453,6 +1460,62 @@ do_nologin(struct passwd *pw)
 }
 
 /*
+ * Test if filesystem is mounted nosuid and nodev
+ */
+static void
+test_nosuid (char * path, dev_t fs)
+{
+       FILE *f;
+       struct stat st;
+       char buf[4096], *s, *on, *mountpoint, *opt;
+       int nodev, nosuid;
+
+       if (!(f = popen ("/bin/mount", "r")))
+               fatal ("%s: popen(\"/bin/mount\", \"r\"): %s",
+                   __func__, strerror (errno));
+       for (;;) {
+               s = fgets (buf, sizeof (buf), f);
+               if (ferror (f))
+                       fatal ("%s: read from popen: %s", __func__,
+                           strerror (errno));
+               if (!s) {
+                       pclose (f);
+                       fatal ("cannot find filesystem with the chroot directory");
+               }
+               (void) strtok (buf, " ");
+               on = strtok (NULL, " ");
+               if (strcmp (on, "on")) {
+                       pclose (f);
+                       fatal ("bad format of mount output");
+               }
+               mountpoint = strtok (NULL, " ");
+               if (memcmp (path, mountpoint, strlen (mountpoint)))
+                       continue;
+               if (stat(mountpoint, &st) != 0) {
+                       pclose (f);
+                       fatal("%s: stat(\"%s\"): %s", __func__,
+                           mountpoint, strerror(errno));
+               }
+               if (fs != st.st_dev)
+                       continue;
+               nodev = nosuid = 0;
+               for (opt = strtok (NULL, "("); opt; opt = strtok (NULL, " ,)")) {
+                       if (!strcmp (opt, "nodev"))
+                               nodev = 1;
+                       else if (!strcmp (opt, "nosuid"))
+                               nosuid = 1;
+                       else if (!strcmp (opt, "noexec"))
+                               nosuid = 1;
+                       if (nodev && nosuid) {
+                               pclose (f);
+                               return;
+                       }
+               }
+               fatal ("chroot into directory without nodev and either noexec or nosuid");
+       }
+}
+
+/*
  * Chroot into a directory after checking it for safety: all path components
  * must be root-owned directories with strict permissions.
  */
@@ -1462,6 +1525,7 @@ safely_chroot(const char *path, uid_t ui
 	const char *cp;
 	char component[PATH_MAX];
 	struct stat st;
+	int last;
 
 	if (*path != '/')
 		fatal("chroot path does not begin at root");
@@ -1473,7 +1537,7 @@ safely_chroot(const char *path, uid_t ui
 	 * root-owned directory with strict permissions.
 	 */
 	for (cp = path; cp != NULL;) {
-		if ((cp = strchr(cp, '/')) == NULL)
+		if (((last = ((cp = strchr(cp, '/')) == NULL))))
 			strlcpy(component, path, sizeof(component));
 		else {
 			cp++;
@@ -1486,7 +1550,7 @@ safely_chroot(const char *path, uid_t ui
 		if (stat(component, &st) != 0)
 			fatal("%s: stat(\"%s\"): %s", __func__,
 			    component, strerror(errno));
-		if (st.st_uid != 0 || (st.st_mode & 022) != 0)
+		if ((st.st_uid != 0 || (st.st_mode & 022) != 0) && !(last && st.st_uid == uid))
 			fatal("bad ownership or modes for chroot "
 			    "directory %s\"%s\"", 
 			    cp == NULL ? "" : "component ", component);
@@ -1495,6 +1559,13 @@ safely_chroot(const char *path, uid_t ui
 			    cp == NULL ? "" : "component ", component);
 
 	}
+	setenv ("TZ", "/etc/localtime", 0);
+	tzset();
+
+	if (st.st_uid) {
+		test_nosuid(path, st.st_dev);
+		++chroot_no_tree;
+	}
 
 	if (chdir(path) == -1)
 		fatal("Unable to chdir to chroot path \"%s\": "
Index: b/sftp-chrootenv.h
===================================================================
--- /dev/null
+++ b/sftp-chrootenv.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2009 Jan F Chadima.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#ifndef CHROOTENV_H
+#define CHROOTENV_H
+
+extern int	chroot_no_tree;
+
+#endif
+
Index: b/sftp-common.c
===================================================================
--- a/sftp-common.c
+++ b/sftp-common.c
@@ -48,6 +48,7 @@
 
 #include "sftp.h"
 #include "sftp-common.h"
+#include "sftp-chrootenv.h"
 
 /* Clear contents of attributes structure */
 void
@@ -221,13 +222,13 @@ ls_file(const char *name, const struct s
 	time_t now;
 
 	strmode(st->st_mode, mode);
-	if (!remote) {
+	if (!remote && !chroot_no_tree) {
 		user = user_from_uid(st->st_uid, 0);
 	} else {
 		snprintf(ubuf, sizeof ubuf, "%u", (u_int)st->st_uid);
 		user = ubuf;
 	}
-	if (!remote) {
+	if (!remote && !chroot_no_tree) {
 		group = group_from_gid(st->st_gid, 0);
 	} else {
 		snprintf(gbuf, sizeof gbuf, "%u", (u_int)st->st_gid);
Index: b/sftp-server-main.c
===================================================================
--- a/sftp-server-main.c
+++ b/sftp-server-main.c
@@ -22,11 +22,14 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <unistd.h>
+#include <time.h>
 
 #include "log.h"
 #include "sftp.h"
 #include "misc.h"
 
+int chroot_no_tree = 0;
+
 void
 cleanup_exit(int i)
 {
Index: b/sftp.c
===================================================================
--- a/sftp.c
+++ b/sftp.c
@@ -117,6 +117,8 @@ int remote_glob(struct sftp_conn *, cons
 
 extern char *__progname;
 
+int chroot_no_tree = 0;
+
 /* Separators for interactive commands */
 #define WHITESPACE " \t\r\n"
 
Index: b/sshd_config.0
===================================================================
--- a/sshd_config.0
+++ b/sshd_config.0
@@ -258,6 +258,14 @@ DESCRIPTION
              (especially those outside the jail).  Misconfiguration can lead
              to unsafe environments which sshd(8) cannot detect.
 
+             In the special case when only sftp is used, not ssh nor scp, it
+             is possible to use ChrootDirectory %h or ChrootDirectory
+             /some/path/%u. The file system containing this directory must be
+             mounted with options nodev and either nosuid or noexec. The owner
+             of the directory should be the user. The ownership of the other
+             components of the path must fulfill the usual conditions. No adi-
+             tional files are required to be present in the directory.
+
              The default is not to chroot(2).
 
      Ciphers
Index: b/sshd_config.5
===================================================================
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -421,6 +421,17 @@ inside the chroot directory on some oper
 .Xr sftp-server 8
 for details).
 .Pp
+In the special case when only sftp is used, not ssh nor scp,
+it is possible to use
+.Cm ChrootDirectory
+%h or
+.Cm ChrootDirectory
+/some/path/%u. The file system containing this directory must be
+mounted with options nodev and either nosuid or noexec. The owner of the
+directory should be the user. The ownership of the other components of the path
+must fulfill the usual conditions. No aditional files are required to be present
+in the directory.
+.Pp
 For safety, it is very important that the directory hierarchy be
 prevented from modification by other processes on the system (especially
 those outside the jail).