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Some "use chroot" improvements.
- The sanitize_paths variable was set too often. It only needs to be set when the "inner" path is not "/". This change avoids sanitizing & munging things for a path=/ module just because chroot is off. - The default for "use chroot" is now "unset" instead of "true". When unset it checks if chrooting works, and if not, it proceeds with a sanitized copy instead of totally failing to work. This makes it easier to setup a non-root rsync daemon, for instance. It will have no effect on a typical Linux root-run daemon where the default will continue to use chroot (because chrooting works). A config file can explicitly set "use chroot = true | false" to force the choice. - Try to improve the "use chroot" manpage.
This commit is contained in:
Wayne Davison
13
NEWS.md
13
NEWS.md
@@ -8,6 +8,9 @@
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- When rsync gets an unpack error on an ACL, mention the filename.
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- Avoid oversetting sanitize_paths when a daemon is serving "/" (even if
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"use chroot" is false).
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### ENHANCEMENTS:
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- Added negotiated daemon-auth support that allows a stronger checksum digest
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@@ -32,6 +35,11 @@
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converted. Newer rsync versions will provide more complete info than older
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versions.
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- The [`use chroot`](#rsyncd.conf) daemon parameter now defaults to "unset" so
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that rsync can test if chrooting works and decide to proceed with a sanitized
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copy if chroot is not supported (e.g., for a non-root daemon). Explicitly
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setting it to true or false (on or off) behaves the same way as before.
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### PACKAGING RELATED:
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- The checksum code now uses openssl's EVP methods, which gets rid of various
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@@ -49,6 +57,11 @@
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configured path in the OPENSSL_CONF environment variable (when the variable
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is not already set). This will enable openssl's MD4 code for rsync to use.
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- The packager may wish to include an explicit "use chroot = true" in the top
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section of the /etc/rsyncd.conf file if the daemon is being installed to run
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as the root user (though rsync should behave the same even with the value
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unset, a little extra paranoia doesn't hurt).
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------------------------------------------------------------------------------
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# NEWS for rsync 3.2.6 (9 Sep 2022)
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@@ -701,7 +701,7 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
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int set_uid;
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char *p, *err_msg = NULL;
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char *name = lp_name(i);
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int use_chroot = lp_use_chroot(i);
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int use_chroot = lp_use_chroot(i); /* might be 1 (yes), 0 (no), or -1 (unset) */
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int ret, pre_exec_arg_fd = -1, pre_exec_error_fd = -1;
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int save_munge_symlinks;
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pid_t pre_exec_pid = 0;
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@@ -826,6 +826,20 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
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io_printf(f_out, "@ERROR: no path setting.\n");
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return -1;
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}
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if (use_chroot < 0) {
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if (strstr(module_dir, "/./") != NULL)
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use_chroot = 1; /* The module is expecting a chroot inner & outer path. */
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else if (chroot("/") < 0) {
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rprintf(FLOG, "chroot test failed: %s. "
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"Switching 'use chroot' from unset to no.\n",
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strerror(errno));
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use_chroot = 0;
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} else {
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if (chdir("/") < 0)
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rsyserr(FLOG, errno, "chdir(\"/\") failed");
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use_chroot = 1;
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}
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}
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if (use_chroot) {
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if ((p = strstr(module_dir, "/./")) != NULL) {
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*p = '\0'; /* Temporary... */
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@@ -962,20 +976,8 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
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}
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if (use_chroot) {
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/*
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* XXX: The 'use chroot' flag is a fairly reliable
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* source of confusion, because it fails under two
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* important circumstances: running as non-root,
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* running on Win32 (or possibly others). On the
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* other hand, if you are running as root, then it
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* might be better to always use chroot.
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*
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* So, perhaps if we can't chroot we should just issue
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* a warning, unless a "require chroot" flag is set,
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* in which case we fail.
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*/
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if (chroot(module_chdir)) {
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rsyserr(FLOG, errno, "chroot %s failed", module_chdir);
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rsyserr(FLOG, errno, "chroot(\"%s\") failed", module_chdir);
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io_printf(f_out, "@ERROR: chroot failed\n");
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return -1;
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}
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@@ -984,7 +986,7 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
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if (!change_dir(module_chdir, CD_NORMAL))
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return path_failure(f_out, module_chdir, True);
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if (module_dirlen || (!use_chroot && !*lp_daemon_chroot()))
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if (module_dirlen)
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sanitize_paths = 1;
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if ((munge_symlinks = lp_munge_symlinks(module_id)) < 0)
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@@ -1299,8 +1301,12 @@ int start_daemon(int f_in, int f_out)
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p = lp_daemon_chroot();
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if (*p) {
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log_init(0); /* Make use we've initialized syslog before chrooting. */
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if (chroot(p) < 0 || chdir("/") < 0) {
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rsyserr(FLOG, errno, "daemon chroot %s failed", p);
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if (chroot(p) < 0) {
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rsyserr(FLOG, errno, "daemon chroot(\"%s\") failed", p);
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return -1;
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}
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if (chdir("/") < 0) {
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rsyserr(FLOG, errno, "daemon chdir(\"/\") failed");
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return -1;
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}
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}
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@@ -60,9 +60,9 @@ BOOL read_only True
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BOOL reverse_lookup True
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BOOL strict_modes True
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BOOL transfer_logging False
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BOOL use_chroot True
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BOOL write_only False
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BOOL3 munge_symlinks Unset
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BOOL3 numeric_ids Unset
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BOOL3 open_noatime Unset
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BOOL3 use_chroot Unset
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@@ -164,6 +164,16 @@ the values of parameters. See the GLOBAL PARAMETERS section for more details.
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available in this module. You must specify this parameter for each module
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in `rsyncd.conf`.
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If the value contains a "/./" element then the path will be divided at that
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point into a chroot dir and an inner-chroot subdir. If [`use chroot`](#)
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is set to false, though, the extraneous dot dir is just cleaned out of the
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path. An example of this idiom is:
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> path = /var/rsync/./module1
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This will (when chrooting) chroot to "/var/rsync" and set the inside-chroot
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path to "/module1".
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You may base the path's value off of an environment variable by surrounding
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the variable name with percent signs. You can even reference a variable
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that is set by rsync when the user connects. For example, this would use
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@@ -187,29 +197,43 @@ the values of parameters. See the GLOBAL PARAMETERS section for more details.
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path, and of complicating the preservation of users and groups by name (see
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below).
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As an additional safety feature, you can specify a dot-dir in the module's
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"[path](#)" to indicate the point where the chroot should occur. This allows
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rsync to run in a chroot with a non-"/" path for the top of the transfer
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hierarchy. Doing this guards against unintended library loading (since
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those absolute paths will not be inside the transfer hierarchy unless you
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have used an unwise pathname), and lets you setup libraries for the chroot
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that are outside of the transfer. For example, specifying
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"/var/rsync/./module1" will chroot to the "/var/rsync" directory and set
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the inside-chroot path to "/module1". If you had omitted the dot-dir, the
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chroot would have used the whole path, and the inside-chroot path would
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have been "/".
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If `use chroot` is not set, it defaults to trying to enable a chroot but
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allows the daemon to continue (after logging a warning) if it fails. The
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one exception to this is when a module's [`path`](#) has a "/./" chroot
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divider in it -- this causes an unset value to be treated as true for that
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module.
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When both "use chroot" and "[daemon chroot](#)" are false, OR the inside-chroot
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path of "use chroot" is not "/", rsync will: (1) munge symlinks by default
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for security reasons (see "[munge symlinks](#)" for a way to turn this off, but
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only if you trust your users), (2) substitute leading slashes in absolute
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paths with the module's path (so that options such as `--backup-dir`,
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`--compare-dest`, etc. interpret an absolute path as rooted in the module's
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"[path](#)" dir), and (3) trim ".." path elements from args if rsync believes
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they would escape the module hierarchy. The default for "use chroot" is
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true, and is the safer choice (especially if the module is not read-only).
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Prior to rsync 3.2.7, the default value was "true". The new default makes
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it easier to setup an rsync daemon as a non-root user or to run a daemon on
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a system where chroot fails. Explicitly setting the value to true in the
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rsyncd.conf file will always require the chroot to succeed.
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When this parameter is enabled *and* the "[name converter](#)" parameter is
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It is also possible to specify a dot-dir in the module's "[path](#)" to
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indicate that you want to chdir to the earlier part of the path and then
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serve files from inside the latter part of the path (with default
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sanitizing and symlink munging). This can be useful if you need some
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library dirs inside the chroot (typically for uid & gid lookups) but don't
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want to put the lib dir into the top of the served path (even though they
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can be hidden with an [`exclude`](#) directive). However, a better choice
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for a modern rsync setup is to use a [`name converter`](#)" and try to
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avoid inner lib dirs altogether. See also the [`daemon chroot`](#)
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parameter, which causes rsync to chroot into its own chroot area before
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doing any path-related chrooting.
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If the daemon is serving the "/" dir (either directly or due to being
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chrooted to the module's path), rsync does not do any extra path sanitizing
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or (default) munging. When it has to limit access to a particular subdir
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(either due to chroot being disabled or having an inside-chroot path set),
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rsync will munge symlinks (by default) and sanitize paths. Those that
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dislike munged symlinks (and really, really trust their users to not break
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out of the subdir) can disable the symlink munging via the "[munge
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symlinks](#)" parameter. Sanitizing paths trims ".." path elements from
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args that rsync believes would escape the module hierarchy, and also
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substitutes leading slashes in absolute paths with the module's path (so
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that options such as `--backup-dir` & `--compare-dest` interpret an
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absolute path as rooted in the module's "[path](#)" dir).
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When a chroot is in effect *and* the "[name converter](#)" parameter is
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*not* set, the "[numeric ids](#)" parameter will default to being enabled
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(disabling name lookups). This means that if you manually setup
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name-lookup libraries in your chroot (instead of using a name converter)
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