syscall: follow trusted sender ancestor links

flist.c

@@ -46,6 +46,7 @@ extern int recurse;
 extern int use_qsort;
 extern int xfer_dirs;
 extern int filesfrom_fd;
+extern char *files_from;
 extern int one_file_system;
 extern int copy_devices;
 extern int copy_dirlinks;
@@ -230,6 +231,189 @@ static int scan_dirfd = -1;
 static const char *scan_dir_prefix;
 static int scan_dir_prefix_len;
 
+struct sender_source_root {
+	struct sender_source_root *next;
+	dev_t dev;
+	ino_t ino;
+	char path[1];
+};
+
+static struct sender_source_root *sender_source_roots;
+
+static int sender_source_full_path(const char *path, char *full, size_t full_size)
+{
+	size_t len;
+
+	if (*path == '/')
+		len = strlcpy(full, path, full_size);
+	else
+		len = pathjoin(full, full_size, curr_dir, path);
+	if (len >= full_size) {
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+	clean_fname(full, CFN_COLLAPSE_DOT_DOT_DIRS | CFN_DROP_TRAILING_DOT_DIR);
+	return 0;
+}
+
+static void remember_sender_source_root(const char *path, const STRUCT_STAT *st)
+{
+	struct sender_source_root *root;
+	char full[MAXPATHLEN];
+	size_t len;
+
+	if (sender_source_full_path(path, full, sizeof full) < 0)
+		overflow_exit("remember_sender_source_root");
+	len = strlen(full);
+
+	for (root = sender_source_roots; root; root = root->next) {
+		if (strcmp(root->path, full) == 0)
+			return;
+	}
+	root = (struct sender_source_root *)new_array(char, sizeof *root + len);
+	root->next = sender_source_roots;
+	root->dev = st->st_dev;
+	root->ino = st->st_ino;
+	memcpy(root->path, full, len + 1);
+	sender_source_roots = root;
+}
+
+static void remember_sender_source_arg(const char *path, const STRUCT_STAT *st)
+{
+	STRUCT_STAT parent_st;
+	char full[MAXPATHLEN], *slash;
+
+	if (S_ISDIR(st->st_mode)) {
+		remember_sender_source_root(path, st);
+		return;
+	}
+	if (sender_source_full_path(path, full, sizeof full) < 0)
+		overflow_exit("remember_sender_source_arg");
+	slash = strrchr(full, '/');
+	if (!slash)
+		return;
+	if (slash == full)
+		slash[1] = '\0';
+	else
+		*slash = '\0';
+	/* The operator selected this parent as part of the source argument. Pin
+	 * its resolved identity while the file leaf remains O_NOFOLLOW later. */
+	if (do_stat(full, &parent_st) == 0 && S_ISDIR(parent_st.st_mode))
+		remember_sender_source_root(full, &parent_st);
+}
+
+int open_sender_source_path(const char *path, int flags, int *matched)
+{
+#if defined AT_FDCWD && defined O_NOFOLLOW && defined O_DIRECTORY
+	struct sender_source_root *root, *best = NULL;
+	STRUCT_STAT st;
+	char full[MAXPATHLEN], *rel;
+	size_t best_len = 0;
+	int rootfd, fd, saved_errno;
+
+	*matched = 0;
+	if (!sender_source_roots)
+		return -1;
+	if (sender_source_full_path(path, full, sizeof full) < 0)
+		return -1;
+	for (root = sender_source_roots; root; root = root->next) {
+		size_t len = strlen(root->path);
+		if (len > best_len && strncmp(full, root->path, len) == 0
+		 && (root->path[len-1] == '/' || full[len] == '\0' || full[len] == '/')) {
+			best = root;
+			best_len = len;
+		}
+	}
+	if (!best)
+		return -1;
+
+	*matched = 1;
+	rootfd = open_anchor_dirfd(best->path);
+	if (rootfd < 0)
+		return -1;
+	if (do_fstat(rootfd, &st) < 0)
+		saved_errno = errno;
+	else if (st.st_dev != best->dev || st.st_ino != best->ino)
+		saved_errno = ELOOP;
+	else
+		saved_errno = 0;
+	if (saved_errno) {
+		close(rootfd);
+		errno = saved_errno;
+		return -1;
+	}
+	rel = full + best_len;
+	while (*rel == '/')
+		rel++;
+	fd = secure_relative_open_at(rootfd, *rel ? rel : ".", flags, 0);
+	saved_errno = errno;
+	close(rootfd);
+	errno = saved_errno;
+	return fd;
+#else
+	*matched = 0;
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
+void clear_sender_source_roots(void)
+{
+	while (sender_source_roots) {
+		struct sender_source_root *root = sender_source_roots;
+		sender_source_roots = root->next;
+		free(root);
+	}
+}
+
+static int filesfrom_owner_walk_active(void)
+{
+	return !am_daemon && am_sender && files_from
+	    && !copy_links && !copy_unsafe_links && !copy_dirlinks && !insecure_links;
+}
+
+static int filesfrom_link_stat(const char *path, STRUCT_STAT *stp, int follow_dirlinks)
+{
+#if defined AT_FDCWD && defined O_NOFOLLOW && defined O_DIRECTORY
+	const char *bname;
+	int dfd, ret, save_errno;
+
+	dfd = owner_walk_parent(path, &bname);
+	if (dfd < 0)
+		return -1;
+	if (am_root < 0) {
+		close(dfd);
+		return link_stat(path, stp, follow_dirlinks);
+	}
+	ret = link_stat_at(dfd, bname, stp, follow_dirlinks);
+	save_errno = ret < 0 ? errno : 0;
+	close(dfd);
+	errno = save_errno;
+	return ret;
+#else
+	return link_stat(path, stp, follow_dirlinks);
+#endif
+}
+
+static int filesfrom_readlink(const char *path, char *linkbuf, size_t bufsiz)
+{
+#if defined AT_FDCWD && defined O_NOFOLLOW && defined O_DIRECTORY
+	const char *bname;
+	int dfd, ret, save_errno;
+
+	dfd = owner_walk_parent(path, &bname);
+	if (dfd < 0)
+		return -1;
+	ret = do_readlink_atfd(dfd, bname, linkbuf, bufsiz);
+	save_errno = ret < 0 ? errno : 0;
+	close(dfd);
+	errno = save_errno;
+	return ret;
+#else
+	return do_readlink(path, linkbuf, bufsiz);
+#endif
+}
+
 static int scan_link_stat(const char *path, STRUCT_STAT *stp, int follow_dirlinks)
 {
 	/* Use the held scan fd only for a single component directly inside the
@@ -241,6 +425,8 @@ static int scan_link_stat(const char *path, STRUCT_STAT *stp, int follow_dirlink
 	 && path[scan_dir_prefix_len] == '/'
 	 && strchr(path + scan_dir_prefix_len + 1, '/') == NULL)
 		return link_stat_at(scan_dirfd, path + scan_dir_prefix_len + 1, stp, follow_dirlinks);
+	if (filesfrom_owner_walk_active())
+		return filesfrom_link_stat(path, stp, follow_dirlinks);
 	return link_stat(path, stp, follow_dirlinks);
 }
 
@@ -251,6 +437,8 @@ static int scan_readlink(const char *path, char *linkbuf, size_t bufsiz)
 	 && path[scan_dir_prefix_len] == '/'
 	 && strchr(path + scan_dir_prefix_len + 1, '/') == NULL)
 		return do_readlink_atfd(scan_dirfd, path + scan_dir_prefix_len + 1, linkbuf, bufsiz);
+	if (filesfrom_owner_walk_active())
+		return filesfrom_readlink(path, linkbuf, bufsiz);
 	return do_readlink(path, linkbuf, bufsiz);
 }
 
@@ -2014,7 +2202,7 @@ static void interpret_stat_error(const char *fname, int is_dir)
 }
 
 #if defined HAVE_FDOPENDIR && defined HAVE_DIRFD
-/* Open a source directory for scanning confined beneath the transfer root.
+/* Open a source directory for scanning under the applicable source authority.
  * secure_relative_open() does a per-component O_NOFOLLOW walk that refuses a
  * parent component raced into a symlink pointing out of the tree; fdopendir()
  * then turns the held fd into the DIR* the scan reads.  This mirrors the
@@ -2025,13 +2213,24 @@ static void interpret_stat_error(const char *fname, int is_dir)
  * O_NOFOLLOW makes secure_relative_open() follow in-tree directory symlinks
  * beneath the anchor and refuse escapes, so this serves both the default
  * no-follow scan and a daemon's symlink-following scan (see the caller).
+ * Files-from entries instead use the ownership walk: their source base is
+ * operator-selected, but each list entry may not be, so only trusted-owned
+ * symlinks are followed and a trusted link may retain its legacy target.
  * Returns NULL with errno set on failure, like opendir(). */
 static DIR *secure_opendir(const char *fbuf)
 {
-	int dfd, fl;
+	int dfd, fl, matched;
 	DIR *d;
 
-	if (am_daemon && (!am_chrooted || module_dirlen)
+	if (filesfrom_owner_walk_active()) {
+		/* The source base is operator-selected, while each list entry may not
+		 * be. Follow only trusted-owned symlinks while opening the directory. */
+		dfd = open_no_attacker_symlinks(fbuf, O_RDONLY | O_DIRECTORY, 0);
+	} else if (!am_daemon && am_sender
+	 && (dfd = open_sender_source_path(fbuf, O_RDONLY | O_DIRECTORY, &matched), matched)) {
+		/* The command-line directory is the operator-selected transfer root.
+		 * Follow that root, then keep every recursive scan beneath its held fd. */
+	} else if (am_daemon && (!am_chrooted || module_dirlen)
 	 && module_dir && module_dir[0] == '/' && *fbuf != '/' && module_dirfd >= 0
 	 && curr_dir_len >= module_dirlen
 	 && strncmp(curr_dir, module_dir, module_dirlen) == 0
@@ -2333,7 +2532,7 @@ static void send1extra(int f, struct file_struct *file, struct file_list *flist)
 	if (file->flags & FLAG_CONTENT_DIR) {
 		if (one_file_system) {
 			STRUCT_STAT st;
-			if (link_stat(fbuf, &st, copy_dirlinks) != 0) {
+			if (scan_link_stat(fbuf, &st, copy_dirlinks) != 0) {
 				interpret_stat_error(fbuf, True);
 				return;
 			}
@@ -2369,7 +2568,7 @@ static void send1extra(int f, struct file_struct *file, struct file_list *flist)
 		if (name_type != NORMAL_NAME) {
 			STRUCT_STAT st = {0};
 
-			if (name_type != MISSING_NAME && link_stat(fbuf, &st, 1) != 0) {
+			if (name_type != MISSING_NAME && scan_link_stat(fbuf, &st, 1) != 0) {
 				interpret_stat_error(fbuf, True);
 				continue;
 			}
@@ -2694,7 +2893,7 @@ struct file_list *send_file_list(int f, int argc, char *argv[])
 		if (fn != fbuf)
 			memmove(fbuf, fn, len + 1);
 
-		if (link_stat(fbuf, &st, copy_dirlinks || name_type != NORMAL_NAME) != 0
+		if (scan_link_stat(fbuf, &st, copy_dirlinks || name_type != NORMAL_NAME) != 0
 		 || (name_type != DOTDIR_NAME && is_excluded(fbuf, S_ISDIR(st.st_mode) != 0, SERVER_FILTERS))
 		 || (relative_paths && path_is_daemon_excluded(fbuf, 1))) {
 			if (errno != ENOENT || missing_args == 0) {
@@ -2724,6 +2923,9 @@ struct file_list *send_file_list(int f, int argc, char *argv[])
 			rprintf(FINFO, "skipping directory %s\n", fbuf);
 			continue;
 		}
+		if (!am_daemon && !use_ff_fd && st.st_mode != 0
+		 && (relative_paths || S_ISDIR(st.st_mode)))
+			remember_sender_source_arg(fbuf, &st);
 
 		if (inc_recurse && relative_paths && *fbuf) {
 			if ((p = strchr(fbuf+1, '/')) != NULL) {

sender.c

@@ -56,6 +56,7 @@ extern char *module_dir;
 extern int module_dirfd;
 extern int write_batch;
 extern int file_old_total;
+extern char *files_from;
 extern BOOL want_progress_now;
 extern struct stats stats;
 extern struct file_list *cur_flist, *first_flist, *dir_flist;
@@ -680,26 +681,27 @@ void send_files(int f_in, int f_out)
 			else
 				fd = sender_open_confined(module_dir, relp, O_RDONLY);
 		} else if (!copy_links && !copy_unsafe_links && !copy_dirlinks && !insecure_links) {
-			/* Default symlink handling (no dir-link following): the scan
-			 * recorded this as a regular file.  Open it confined beneath the
-			 * transfer root: an in-tree symlinked parent (e.g. -R keeps one in
-			 * the path) is followed beneath the root, a parent raced into a
-			 * symlink pointing out of the tree is refused, and O_NOFOLLOW
-			 * governs the leaf so a raced leaf symlink is refused.  A
-			 * symlink-following mode (-L/--copy-unsafe-links/-k) or
-			 * --insecure-links keeps the legacy open below. */
-			if (fname[0] == '/') {
-				/* --relative (or a --files-from absolute name) keeps the
-				 * full absolute path as fname; the transfer root is then "/",
-				 * so anchor the confined open there and strip the leading
-				 * slash to the module-relative path the resolver wants -- it
-				 * rejects an absolute relpath outright. */
-				const char *relp = fname;
-				while (*relp == '/')
-					relp++;
-				fd = sender_open_confined("/", relp, O_RDONLY);
-			} else
-				fd = sender_open_confined(NULL, fname, O_RDONLY);
+			int matched;
+			/* A files-from entry follows only trusted-owned ancestors because
+			 * its source base is operator-selected but the entry itself may not
+			 * be. Other paths stay confined beneath their explicit transfer root.
+			 * Every file leaf remains O_NOFOLLOW. */
+			if (files_from) {
+				fd = do_open_checklinks(fname);
+			} else {
+				fd = open_sender_source_path(fname, O_RDONLY | O_NOFOLLOW, &matched);
+				if (!matched) {
+					if (fname[0] == '/') {
+						/* --relative keeps the full absolute path as fname;
+						 * anchor at "/" and pass the resolver a relative path. */
+						const char *relp = fname;
+						while (*relp == '/')
+							relp++;
+						fd = sender_open_confined("/", relp, O_RDONLY);
+					} else
+						fd = sender_open_confined(NULL, fname, O_RDONLY);
+				}
+			}
 		} else {
 			fd = do_open_checklinks(fname);
 		}
@@ -809,6 +811,7 @@ void send_files(int f_in, int f_out)
 	if (DEBUG_GTE(SEND, 1))
 		rprintf(FINFO, "send files finished\n");
 
+	clear_sender_source_roots();
 	match_report();
 
 	write_ndx(f_out, NDX_DONE);