1 files changed, 93 insertions, 0 deletions
diff --git a/util.c b/util.c
index b708527..0ec6dba 100644
--- a/util.c
+++ b/util.c
@@ -30,6 +30,10 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#if BFS_HAS_POSIX1E_CAPABILITIES
+#	include <sys/capability.h>
+#endif
+
 #if BFS_HAS_SYS_PARAM
 #	include <sys/param.h>
 #endif
@@ -377,3 +381,92 @@ int bfs_minor(dev_t dev) {
 	return dev & 0xFF;
 #endif
 }
+
+#if BFS_HAS_POSIX1E_CAPABILITIES
+
+static const char *open_path(const struct BFTW *ftwbuf, int *fd) {
+#ifdef O_PATH
+	// The POSIX.1e APIS predate the *at() family of functions.  We'd still
+	// like to do something to avoid path re-traversals and limit races
+	// though.  Ideally we could just do openat(..., O_PATH) (since we may
+	// not have read access) and pass that fd to something like cap_get_fd()
+	// but that will fail since fgetxattr() needs read access to the file.
+	// The workaround is to use O_PATH to open an fd and then pass
+	// /proc/self/fd/<fd> to cap_get_path().  Inspired by
+	// https://android.googlesource.com/platform/bionic/+/2825f10b7f61558c264231a536cf3affc0d84204
+	int flags = O_PATH;
+	if (ftwbuf->at_flags & AT_SYMLINK_NOFOLLOW) {
+		flags |= O_NOFOLLOW;
+	}
+
+	*fd = openat(ftwbuf->at_fd, ftwbuf->at_path, flags);
+	if (*fd < 0) {
+		return NULL;
+	}
+
+	size_t size = strlen("/proc/self/fd/") + CHAR_BIT*sizeof(int) + 1;
+	char *path = malloc(size);
+	if (!path) {
+		close(*fd);
+		*fd = -1;
+		return NULL;
+	}
+
+	snprintf(path, size, "/proc/self/fd/%d", *fd);
+	return path;
+#else
+	*fd = -1;
+	return ftwbuf->path;
+#endif
+}
+
+static void close_path(const struct BFTW *ftwbuf, const char *path, int fd) {
+	if (path && path != ftwbuf->path) {
+		free((void *)path);
+	}
+	if (fd >= 0) {
+		close(fd);
+	}
+}
+
+bool bfs_check_capabilities(const struct BFTW *ftwbuf) {
+	bool ret = false;
+
+	if (ftwbuf->typeflag == BFTW_LNK) {
+		goto out;
+	}
+
+	int fd;
+	const char *path = open_path(ftwbuf, &fd);
+	if (!path) {
+		goto out;
+	}
+
+	cap_t caps = cap_get_file(path);
+	if (!caps) {
+		goto out_close;
+	}
+
+	// TODO: Any better way to check for a non-empty capability set?
+	char *text = cap_to_text(caps, NULL);
+	if (!text) {
+		goto out_free_caps;
+	}
+	ret = text[0];
+
+	cap_free(text);
+out_free_caps:
+	cap_free(caps);
+out_close:
+	close_path(ftwbuf, path, fd);
+out:
+	return ret;
+}
+
+#else // !BFS_HAS_POSIX1E_CAPABILITIES
+
+bool bfs_check_capabilities(const struct BFTW *ftwbuf) {
+	return false;
+}
+
+#endif