Some extra file-list safety checks.

exclude.c

@@ -27,16 +27,22 @@ extern int am_server;
 extern int am_sender;
 extern int eol_nulls;
 extern int io_error;
+extern int xfer_dirs;
+extern int recurse;
 extern int local_server;
 extern int prune_empty_dirs;
 extern int ignore_perishable;
+extern int old_style_args;
+extern int relative_paths;
 extern int delete_mode;
 extern int delete_excluded;
 extern int cvs_exclude;
 extern int sanitize_paths;
 extern int protocol_version;
+extern int list_only;
 extern int module_id;
 
+extern char *filesfrom_host;
 extern char curr_dir[MAXPATHLEN];
 extern unsigned int curr_dir_len;
 extern unsigned int module_dirlen;
@@ -44,8 +50,10 @@ extern unsigned int module_dirlen;
 filter_rule_list filter_list = { .debug_type = "" };
 filter_rule_list cvs_filter_list = { .debug_type = " [global CVS]" };
 filter_rule_list daemon_filter_list = { .debug_type = " [daemon]" };
+filter_rule_list implied_filter_list = { .debug_type = " [implied]" };
 
 int saw_xattr_filter = 0;
+int trust_sender_filter = 0;
 
 /* Need room enough for ":MODS " prefix plus some room to grow. */
 #define MAX_RULE_PREFIX (16)
@@ -292,6 +300,125 @@ static void add_rule(filter_rule_list *listp, const char *pat, unsigned int pat_
 	}
 }
 
+/* Each arg the client sends to the remote sender turns into an implied include
+ * that the receiver uses to validate the file list from the sender. */
+void add_implied_include(const char *arg)
+{
+	filter_rule *rule;
+	int arg_len, saw_wild = 0, backslash_cnt = 0;
+	int slash_cnt = 1; /* We know we're adding a leading slash. */
+	const char *cp;
+	char *p;
+	if (old_style_args || list_only || filesfrom_host != NULL)
+		return;
+	if (relative_paths) {
+		cp = strstr(arg, "/./");
+		if (cp)
+			arg = cp+3;
+	} else {
+		if ((cp = strrchr(arg, '/')) != NULL)
+			arg = cp + 1;
+	}
+	arg_len = strlen(arg);
+	if (arg_len) {
+		if (strpbrk(arg, "*[?")) {
+			/* We need to add room to escape backslashes if wildcard chars are present. */
+			cp = arg;
+			while ((cp = strchr(cp, '\\')) != NULL) {
+				arg_len++;
+				cp++;
+			}
+			saw_wild = 1;
+		}
+		arg_len++; /* Leave room for the prefixed slash */
+		rule = new0(filter_rule);
+		if (!implied_filter_list.head)
+			implied_filter_list.head = implied_filter_list.tail = rule;
+		else {
+			rule->next = implied_filter_list.head;
+			implied_filter_list.head = rule;
+		}
+		rule->rflags = FILTRULE_INCLUDE + (saw_wild ? FILTRULE_WILD : 0);
+		p = rule->pattern = new_array(char, arg_len + 1);
+		*p++ = '/';
+		cp = arg;
+		while (*cp) {
+			switch (*cp) {
+			  case '\\':
+				backslash_cnt++;
+				if (saw_wild)
+					*p++ = '\\';
+				*p++ = *cp++;
+				break;
+			  case '/':
+				if (p[-1] == '/') /* This is safe because of the initial slash. */
+					break;
+				if (relative_paths) {
+					filter_rule const *ent;
+					int found = 0;
+					*p = '\0';
+					for (ent = implied_filter_list.head; ent; ent = ent->next) {
+						if (ent != rule && strcmp(ent->pattern, rule->pattern) == 0)
+							found = 1;
+					}
+					if (!found) {
+						filter_rule *R_rule = new0(filter_rule);
+						R_rule->rflags = FILTRULE_INCLUDE + (saw_wild ? FILTRULE_WILD : 0);
+						R_rule->pattern = strdup(rule->pattern);
+						R_rule->u.slash_cnt = slash_cnt;
+						R_rule->next = implied_filter_list.head;
+						implied_filter_list.head = R_rule;
+					}
+				}
+				slash_cnt++;
+				*p++ = *cp++;
+				break;
+			  default:
+				*p++ = *cp++;
+				break;
+			}
+		}
+		*p = '\0';
+		rule->u.slash_cnt = slash_cnt;
+		arg = (const char *)rule->pattern;
+	}
+
+	if (recurse || xfer_dirs) {
+		/* Now create a rule with an added "/" & "**" or "*" at the end */
+		rule = new0(filter_rule);
+		if (recurse)
+			rule->rflags = FILTRULE_INCLUDE | FILTRULE_WILD | FILTRULE_WILD2;
+		else
+			rule->rflags = FILTRULE_INCLUDE | FILTRULE_WILD;
+		/* A +4 in the len leaves enough room for / * * \0 or / * \0 \0 */
+		if (!saw_wild && backslash_cnt) {
+			/* We are appending a wildcard, so now the backslashes need to be escaped. */
+			p = rule->pattern = new_array(char, arg_len + backslash_cnt + 3 + 1);
+			cp = arg;
+			while (*cp) {
+				if (*cp == '\\')
+					*p++ = '\\';
+				*p++ = *cp++;
+			}
+		} else {
+			p = rule->pattern = new_array(char, arg_len + 3 + 1);
+			if (arg_len) {
+				memcpy(p, arg, arg_len);
+				p += arg_len;
+			}
+		}
+		if (p[-1] != '/')
+			*p++ = '/';
+		*p++ = '*';
+		if (recurse)
+			*p++ = '*';
+		*p = '\0';
+		rule->u.slash_cnt = slash_cnt + 1;
+		rule->next = implied_filter_list.head;
+		implied_filter_list.head = rule;
+	}
+}
+
 /* This frees any non-inherited items, leaving just inherited items on the list. */
 static void pop_filter_list(filter_rule_list *listp)
 {
@@ -718,7 +845,7 @@ static void report_filter_result(enum logcode code, char const *name,
 			      : name_flags & NAME_IS_DIR ? "directory"
 			      : "file";
 		rprintf(code, "[%s] %sing %s %s because of pattern %s%s%s\n",
-		    w, actions[*w!='s'][!(ent->rflags & FILTRULE_INCLUDE)],
+		    w, actions[*w=='g'][!(ent->rflags & FILTRULE_INCLUDE)],
 		    t, name, ent->pattern,
 		    ent->rflags & FILTRULE_DIRECTORY ? "/" : "", type);
 	}
@@ -890,6 +1017,7 @@ static filter_rule *parse_rule_tok(const char **rulestr_ptr,
 		}
 		switch (ch) {
 		case ':':
+			trust_sender_filter = 1;
 			rule->rflags |= FILTRULE_PERDIR_MERGE
 				      | FILTRULE_FINISH_SETUP;
 			/* FALL THROUGH */

flist.c

@@ -73,6 +73,7 @@ extern int need_unsorted_flist;
 extern int sender_symlink_iconv;
 extern int output_needs_newline;
 extern int sender_keeps_checksum;
+extern int trust_sender_filter;
 extern int unsort_ndx;
 extern uid_t our_uid;
 extern struct stats stats;
@@ -83,8 +84,7 @@ extern char curr_dir[MAXPATHLEN];
 
 extern struct chmod_mode_struct *chmod_modes;
 
-extern filter_rule_list filter_list;
-extern filter_rule_list daemon_filter_list;
+extern filter_rule_list filter_list, implied_filter_list, daemon_filter_list;
 
 #ifdef ICONV_OPTION
 extern int filesfrom_convert;
@@ -986,6 +986,19 @@ static struct file_struct *recv_file_entry(int f, struct file_list *flist, int x
 		exit_cleanup(RERR_UNSUPPORTED);
 	}
 
+	if (*thisname != '.' || thisname[1] != '\0') {
+		int filt_flags = S_ISDIR(mode) ? NAME_IS_DIR : NAME_IS_FILE;
+		if (!trust_sender_filter /* a per-dir filter rule means we must trust the sender's filtering */
+		 && filter_list.head && check_filter(&filter_list, FINFO, thisname, filt_flags) < 0) {
+			rprintf(FERROR, "ERROR: rejecting excluded file-list name: %s\n", thisname);
+			exit_cleanup(RERR_PROTOCOL);
+		}
+		if (implied_filter_list.head && check_filter(&implied_filter_list, FINFO, thisname, filt_flags) <= 0) {
+			rprintf(FERROR, "ERROR: rejecting unrequested file-list name: %s\n", thisname);
+			exit_cleanup(RERR_PROTOCOL);
+		}
+	}
+
 	if (inc_recurse && S_ISDIR(mode)) {
 		if (one_file_system) {
 			/* Room to save the dir's device for -x */

io.c

@@ -419,6 +419,7 @@ static void forward_filesfrom_data(void)
 		while (s != eob) {
 			if (*s++ == '\0') {
 				ff_xb.len = s - sob - 1;
+				add_implied_include(sob);
 				if (iconvbufs(ic_send, &ff_xb, &iobuf.out, flags) < 0)
 					exit_cleanup(RERR_PROTOCOL); /* impossible? */
 				write_buf(iobuf.out_fd, s-1, 1); /* Send the '\0'. */
@@ -450,9 +451,12 @@ static void forward_filesfrom_data(void)
 		char *f = ff_xb.buf + ff_xb.pos;
 		char *t = ff_xb.buf;
 		char *eob = f + len;
+		char *cur = t;
 		/* Eliminate any multi-'\0' runs. */
 		while (f != eob) {
 			if (!(*t++ = *f++)) {
+				add_implied_include(cur);
+				cur = t;
 				while (f != eob && *f == '\0')
 					f++;
 			}

main.c

@@ -89,6 +89,7 @@ extern int backup_dir_len;
 extern int basis_dir_cnt;
 extern int default_af_hint;
 extern int stdout_format_has_i;
+extern int trust_sender_filter;
 extern struct stats stats;
 extern char *stdout_format;
 extern char *logfile_format;
@@ -104,7 +105,7 @@ extern char curr_dir[MAXPATHLEN];
 extern char backup_dir_buf[MAXPATHLEN];
 extern char *basis_dir[MAX_BASIS_DIRS+1];
 extern struct file_list *first_flist;
-extern filter_rule_list daemon_filter_list;
+extern filter_rule_list daemon_filter_list, implied_filter_list;
 
 uid_t our_uid;
 gid_t our_gid;
@@ -635,6 +636,7 @@ static pid_t do_cmd(char *cmd, char *machine, char *user, char **remote_argv, in
 #ifdef ICONV_CONST
 		setup_iconv();
 #endif
+		trust_sender_filter = 1;
 	} else if (local_server) {
 		/* If the user didn't request --[no-]whole-file, force
 		 * it on, but only if we're not batch processing. */
@@ -1500,6 +1502,8 @@ static int start_client(int argc, char *argv[])
 		char *dummy_host;
 		int dummy_port = rsync_port;
 		int i;
+		if (filesfrom_fd < 0)
+			add_implied_include(remote_argv[0]);
 		/* For remote source, any extra source args must have either
 		 * the same hostname or an empty hostname. */
 		for (i = 1; i < remote_argc; i++) {
@@ -1523,6 +1527,7 @@ static int start_client(int argc, char *argv[])
 			if (!rsync_port && !*arg) /* Turn an empty arg into a dot dir. */
 				arg = ".";
 			remote_argv[i] = arg;
+			add_implied_include(arg);
 		}
 	}
 

receiver.c

@@ -593,10 +593,13 @@ int recv_files(int f_in, int f_out, char *local_name)
 		if (DEBUG_GTE(RECV, 1))
 			rprintf(FINFO, "recv_files(%s)\n", fname);
 
-		if (daemon_filter_list.head && (*fname != '.' || fname[1] != '\0')
-		 && check_filter(&daemon_filter_list, FLOG, fname, 0) < 0) {
-			rprintf(FERROR, "attempt to hack rsync failed.\n");
-			exit_cleanup(RERR_PROTOCOL);
+		if (daemon_filter_list.head && (*fname != '.' || fname[1] != '\0')) {
+			int filt_flags = S_ISDIR(file->mode) ? NAME_IS_DIR : NAME_IS_FILE;
+			if (check_filter(&daemon_filter_list, FLOG, fname, filt_flags) < 0) {
+				rprintf(FERROR, "ERROR: rejecting file transfer request for daemon excluded file: %s\n",
+					fname);
+				exit_cleanup(RERR_PROTOCOL);
+			}
 		}
 
 #ifdef SUPPORT_XATTRS

rsync.1.md

@@ -167,6 +167,33 @@ separate the files into different rsync calls, or consider using
 [`--delay-updates`](#opt) (which doesn't affect the sorted transfer order, but
 does make the final file-updating phase happen much more rapidly).
 
+## MULTI-HOST SECURITY
+
+Rsync takes steps to ensure that the file requests that are shared in a
+transfer are protected against various security issues.  Most of the potential
+problems arise on the receiving side where rsync takes steps to ensure that the
+list of files being transferred remains within the bounds of what was
+requested.
+
+Toward this end, rsync 3.1.2 and later have aborted when a file list contains
+an absolute or relative path that tries to escape out of the top of the
+transfer.  Also, beginning with version 3.2.5, rsync does two more safety
+checks of the file list to (1) ensure that no extra source arguments were added
+into the transfer other than those that the client requested and (2) ensure
+that the file list obeys the exclude rules that we sent to the sender.
+
+For those that don't yet have a 3.2.5 client rsync, it is safest to do a copy
+into a dedicated destination directory for the remote files rather than
+requesting the remote content get mixed in with other local content.  For
+example, doing an rsync copy into your home directory is potentially unsafe on
+an older rsync if the remote rsync is being controlled by a bad actor:
+
+>     rsync -aiv host1:dir1 ~
+
+A safer command would be:
+
+>     rsync -aiv host1:dir1 ~/host1-files
+
 ## ADVANCED USAGE
 
 The syntax for requesting multiple files from a remote host is done by
@@ -187,7 +214,7 @@ Starting in 3.2.4, filenames are passed to a remote shell in such a way as to
 preserve the characters you give it. Thus, if you ask for a file with spaces
 in the name, that's what the remote rsync looks for:
 
->     rsync -aiv host:'a simple file.pdf' /dest/                                                                                
+>     rsync -aiv host:'a simple file.pdf' /dest/
 
 If you use scripts that have been written to manually apply extra quoting to
 the remote rsync args (or to require remote arg splitting), you can ask rsync
@@ -2343,6 +2370,12 @@ option name from the pathname using a space if you want the shell to expand it.
     behavior.  The environment is always overridden by manually specified
     positive or negative options (the negative is `--no-old-args`).
 
+    Note that this option also disables the extra safety check added in 3.2.5
+    that ensures that a remote sender isn't including extra top-level items in
+    the file-list that you didn't request.  This side-effect is necessary
+    because we can't know for sure what names to expect when the remote shell
+    is interpreting the args.
+
     This option conflicts with the [`--protect-args`](#opt) option.
 
 0.  `--protect-args`, `-s`
@@ -3894,8 +3927,13 @@ Here are the available rule prefixes:
     `hide` and a `protect`.
 0.  `include, '+'` specifies an include pattern that (by default) is both a
     `show` and a `risk`.
-0.  `merge, '.'` specifies a merge-file to read for more rules.
-0.  `dir-merge, ':'` specifies a per-directory merge-file.
+0.  `merge, '.'` specifies a merge-file on the client side to read for more
+    rules.
+0.  `dir-merge, ':'` specifies a per-directory merge-file.  Using this kind of
+    filter rule requires that you trust the sending side's filter checking, and
+    thus it disables the receiver's verification of the file-list names against
+    the filter rules (since only the sender can know for sure if it obeyed all
+    the filter rules when some are per-dir merged from the sender's files).
 0.  `hide, 'H'` specifies a pattern for hiding files from the transfer.
     Equivalent to a sender-only exclude, so `-f'H foo'` could also be specified
     as `-f'-s foo'`.