libsandbox: reject "" paths with *at funcs before checking the dirfd [missing file]

When it comes to processing errors, an empty path is checked before
an invalid dirfd.  Make sure sandbox matches that behavior for the
random testsuites out there that look for this.

Forgot to `git add` in the previous commit :/.

URL: https://bugs.gentoo.org/346929
Reported-by: Marien Zwart <marienz@gentoo.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/libsandbox/wrapper-funcs/__pre_at_check.c b/libsandbox/wrapper-funcs/__pre_at_check.c
new file mode 100644
index 0000000..f72c40c
--- /dev/null
+++ b/libsandbox/wrapper-funcs/__pre_at_check.c
@@ -0,0 +1,34 @@
+/*
+ * common *at() pre-checks.
+ *
+ * Copyright 1999-2012 Gentoo Foundation
+ * Licensed under the GPL-2
+ */
+
+/* We assume the parent has nested use with save/restore errno */
+bool sb_common_at_pre_check(const char *func, const char **pathname, int dirfd,
+                            char *dirfd_path, size_t dirfd_path_len)
+{
+	/* the empty path name should fail with ENOENT before any dirfd
+	 * checks get a chance to run #346929
+	 */
+	if (*pathname && *pathname[0] == '\0') {
+		errno = ENOENT;
+		sb_debug_dyn("EARLY FAIL: %s(%s): %s\n",
+			func, *pathname, strerror(errno));
+		return false;
+	}
+
+	/* Expand the dirfd path first */
+	switch (resolve_dirfd_path(dirfd, *pathname, dirfd_path, dirfd_path_len)) {
+		case -1:
+			sb_debug_dyn("EARLY FAIL: %s(%s) @ resolve_dirfd_path: %s\n",
+				func, *pathname, strerror(errno));
+			return false;
+		case 0:
+			*pathname = dirfd_path;
+			break;
+	}
+
+	return true;
+}