Don't canonicalize named file descriptors that reference special objects.

Named file descriptors may reference special objects like pipes,
sockets, inodes, ...  Such objects do not belong to the file-system.

src/path/path.c

@@ -412,6 +412,12 @@ int translate_path(Tracee *tracee, char result[PATH_MAX], int dir_fd,
 		if (status < 0)
 			return status;
 
+		/* Named file descriptors may reference special
+		 * objects like pipes, sockets, inodes, ...  Such
+		 * objects do not belong to the file-system.  */
+		if (result[0] != '/')
+			return -ENOTDIR;
+
 		/* Remove the leading "root" part of the base
 		 * (required!). */
 		status = detranslate_path(tracee, result, NULL);

tests/GNUmakefile

@@ -70,6 +70,9 @@ check-test-a3e68988.c: test-a3e68988
 	@which gdb >/dev/null 2>&1 || rm -f $<
 	$(call check_c,$<,$(PROOT) gdb -return-child-result -ex run -ex quit ./$<)
 
+check-test-fdf487a0.c: test-fdf487a0
+	$(call check_c,$<,echo test | $(PROOT) ./$<)
+
 check_c = $(Q)if [ -e $< ]; then			\
 		$(2) $(silently); $(call check,$(1))	\
 	else						\
@@ -144,6 +147,9 @@ test-c5a7a0f0: test-c5a7a0f0.c
 test-a3e68988: test-a3e68988.c
 	$(Q)$(CC) $< -o $@ $(silently) || true
 
+test-fdf487a0: test-fdf487a0.c
+	$(Q)$(CC) $< -o $@ $(silently) || true
+
 ######################################################################
 # Beautified output
 

tests/test-fdf487a0.c

@@ -0,0 +1,31 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+int main()
+{
+	int fd;
+
+	fd = openat(0, "foo", O_RDONLY);
+	if (fd >= 0 || errno != ENOTDIR) {
+		printf("1. %d %d\n", fd, (int) errno);
+		exit(EXIT_FAILURE);
+	}
+
+	fd = openat(0, "", O_RDONLY);
+	if (fd >= 0 || errno != ENOENT) {
+		printf("2. %d %d\n", fd, (int) errno);
+		exit(EXIT_FAILURE);
+	}
+
+	fd = openat(0, NULL, O_RDONLY);
+	if (fd >= 0 || errno != EFAULT) {
+		printf("3. %d %d\n", fd, (int) errno);
+		exit(EXIT_FAILURE);
+	}
+
+	exit(EXIT_SUCCESS);
+}