bpftool: Use only nftw for file tree parsing

The bpftool sources include code to walk file trees, but use multiple
frameworks to do so: nftw and fts. While nftw conforms to POSIX/SUSv3 and
is widely available, fts is not conformant and less common, especially on
non-glibc systems. The inconsistent framework usage hampers maintenance
and portability of bpftool, in particular for embedded systems.

Standardize code usage by rewriting one fts-based function to use nftw and
clean up some related function warnings by extending use of "const char *"
arguments. This change helps in building bpftool against musl for OpenWrt.

Also fix an unsafe call to dirname() by duplicating the string to pass,
since some implementations may directly alter it. The same approach is
used in libbpf.c.

Signed-off-by: Tony Ambardar <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Reviewed-by: Quentin Monnet <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/bpf/bpftool/common.c

···
 // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /* Copyright (C) 2017-2018 Netronome Systems, Inc. */
 
+#define _GNU_SOURCE
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <fts.h>
+#include <ftw.h>
 #include <libgen.h>
 #include <mntent.h>
 #include <stdbool.h>
···
 	return err;
 }
 
-int open_obj_pinned(char *path, bool quiet)
+int open_obj_pinned(const char *path, bool quiet)
 {
-	int fd;
+	char *pname;
+	int fd = -1;
 
-	fd = bpf_obj_get(path);
-	if (fd < 0) {
+	pname = strdup(path);
+	if (!pname) {
 		if (!quiet)
-			p_err("bpf obj get (%s): %s", path,
-			      errno == EACCES && !is_bpffs(dirname(path)) ?
-			    "directory not in bpf file system (bpffs)" :
-			    strerror(errno));
-		return -1;
+			p_err("mem alloc failed");
+		goto out_ret;
 	}
 
+	fd = bpf_obj_get(pname);
+	if (fd < 0) {
+		if (!quiet)
+			p_err("bpf obj get (%s): %s", pname,
+			      errno == EACCES && !is_bpffs(dirname(pname)) ?
+			    "directory not in bpf file system (bpffs)" :
+			    strerror(errno));
+		goto out_free;
+	}
+
+out_free:
+	free(pname);
+out_ret:
 	return fd;
 }
 
-int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type)
+int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type)
 {
 	enum bpf_obj_type type;
 	int fd;
···
 	jsonw_end_array(json_wtr);
 }
 
+/* extra params for nftw cb */
+static struct pinned_obj_table *build_fn_table;
+static enum bpf_obj_type build_fn_type;
+
+static int do_build_table_cb(const char *fpath, const struct stat *sb,
+			     int typeflag, struct FTW *ftwbuf)
+{
+	struct bpf_prog_info pinned_info;
+	__u32 len = sizeof(pinned_info);
+	struct pinned_obj *obj_node;
+	enum bpf_obj_type objtype;
+	int fd, err = 0;
+
+	if (typeflag != FTW_F)
+		goto out_ret;
+
+	fd = open_obj_pinned(fpath, true);
+	if (fd < 0)
+		goto out_ret;
+
+	objtype = get_fd_type(fd);
+	if (objtype != build_fn_type)
+		goto out_close;
+
+	memset(&pinned_info, 0, sizeof(pinned_info));
+	if (bpf_obj_get_info_by_fd(fd, &pinned_info, &len))
+		goto out_close;
+
+	obj_node = calloc(1, sizeof(*obj_node));
+	if (!obj_node) {
+		err = -1;
+		goto out_close;
+	}
+
+	obj_node->id = pinned_info.id;
+	obj_node->path = strdup(fpath);
+	if (!obj_node->path) {
+		err = -1;
+		free(obj_node);
+		goto out_close;
+	}
+
+	hash_add(build_fn_table->table, &obj_node->hash, obj_node->id);
+out_close:
+	close(fd);
+out_ret:
+	return err;
+}
+
 int build_pinned_obj_table(struct pinned_obj_table *tab,
 			   enum bpf_obj_type type)
 {
-	struct bpf_prog_info pinned_info = {};
-	struct pinned_obj *obj_node = NULL;
-	__u32 len = sizeof(pinned_info);
 	struct mntent *mntent = NULL;
-	enum bpf_obj_type objtype;
 	FILE *mntfile = NULL;
-	FTSENT *ftse = NULL;
-	FTS *fts = NULL;
-	int fd, err;
+	int flags = FTW_PHYS;
+	int nopenfd = 16;
+	int err = 0;
 
 	mntfile = setmntent("/proc/mounts", "r");
 	if (!mntfile)
 		return -1;
 
+	build_fn_table = tab;
+	build_fn_type = type;
+
 	while ((mntent = getmntent(mntfile))) {
-		char *path[] = { mntent->mnt_dir, NULL };
+		char *path = mntent->mnt_dir;
 
 		if (strncmp(mntent->mnt_type, "bpf", 3) != 0)
 			continue;
-
-		fts = fts_open(path, 0, NULL);
-		if (!fts)
-			continue;
-
-		while ((ftse = fts_read(fts))) {
-			if (!(ftse->fts_info & FTS_F))
-				continue;
-			fd = open_obj_pinned(ftse->fts_path, true);
-			if (fd < 0)
-				continue;
-
-			objtype = get_fd_type(fd);
-			if (objtype != type) {
-				close(fd);
-				continue;
-			}
-			memset(&pinned_info, 0, sizeof(pinned_info));
-			err = bpf_obj_get_info_by_fd(fd, &pinned_info, &len);
-			if (err) {
-				close(fd);
-				continue;
-			}
-
-			obj_node = malloc(sizeof(*obj_node));
-			if (!obj_node) {
-				close(fd);
-				fts_close(fts);
-				fclose(mntfile);
-				return -1;
-			}
-
-			memset(obj_node, 0, sizeof(*obj_node));
-			obj_node->id = pinned_info.id;
-			obj_node->path = strdup(ftse->fts_path);
-			hash_add(tab->table, &obj_node->hash, obj_node->id);
-
-			close(fd);
-		}
-		fts_close(fts);
+		err = nftw(path, do_build_table_cb, nopenfd, flags);
+		if (err)
+			break;
 	}
 	fclose(mntfile);
-	return 0;
+	return err;
 }
 
 void delete_pinned_obj_table(struct pinned_obj_table *tab)

tools/bpf/bpftool/main.h

···
 int get_fd_type(int fd);
 const char *get_fd_type_name(enum bpf_obj_type type);
 char *get_fdinfo(int fd, const char *key);
-int open_obj_pinned(char *path, bool quiet);
-int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type);
+int open_obj_pinned(const char *path, bool quiet);
+int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type);
 int mount_bpffs_for_pin(const char *name);
 int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(int *, char ***));
 int do_pin_fd(int fd, const char *name);