selftests/exec: Verify execve of non-regular files fail

Add a named pipe as an exec target to make sure that non-regular
files are rejected by execve() with EACCES. This can help verify
commit 73601ea5 ("fs/open.c: allow opening only regular files
during execve()").
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/exec/.gitignore

@@ -9,3 +9,4 @@ execveat.ephemeral
 execveat.denatured
 /recursion-depth
 xxxxxxxx*
+pipe

tools/testing/selftests/exec/Makefile

@@ -4,7 +4,7 @@ CFLAGS += -Wno-nonnull
 CFLAGS += -D_GNU_SOURCE
 
 TEST_GEN_PROGS := execveat
-TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir
+TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir pipe
 # Makefile is a run-time dependency, since it's accessed by the execveat test
 TEST_FILES := Makefile
 

tools/testing/selftests/exec/execveat.c

@@ -5,7 +5,9 @@
  * Selftests for execveat(2).
  */
 
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE  /* to get O_PATH, AT_EMPTY_PATH */
+#endif
 #include <sys/sendfile.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
@@ -311,6 +313,10 @@ static int run_tests(void)
 	fail += check_execveat_fail(AT_FDCWD, fullname_symlink,
 				    AT_SYMLINK_NOFOLLOW, ELOOP);
 
+	/*  Non-regular file failure */
+	fail += check_execveat_fail(dot_dfd, "pipe", 0, EACCES);
+	unlink("pipe");
+
 	/* Shell script wrapping executable file: */
 	/*   dfd + path */
 	fail += check_execveat(subdir_dfd, "../script", 0);
@@ -384,6 +390,8 @@ static void prerequisites(void)
 	fd = open("subdir.ephemeral/script", O_RDWR|O_CREAT|O_TRUNC, 0755);
 	write(fd, script, strlen(script));
 	close(fd);
+
+	mkfifo("pipe", 0755);
 }
 
 int main(int argc, char **argv)