audit small applets and mark some of them as NOFORK.

Put big scary warnings in relevant places.

libbb/copyfd.c

@@ -7,19 +7,15 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
 
-#include <errno.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-
 #include "libbb.h"
 
-
 #if BUFSIZ < 4096
 #undef BUFSIZ
 #define BUFSIZ 4096
 #endif
 
+/* Used by NOFORK applets (e.g. cat) - must be very careful
+ * when calling xfuncs, allocating memory, with signals, termios, etc... */
 
 static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
 {
@@ -27,7 +23,8 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
 	off_t total = 0;
 	RESERVE_CONFIG_BUFFER(buffer, BUFSIZ);
 
-	if (src_fd < 0) goto out;
+	if (src_fd < 0)
+		goto out;
 
 	if (!size) {
 		size = BUFSIZ;

libbb/fflush_stdout_and_exit.c

@@ -13,6 +13,10 @@
 
 #include "libbb.h"
 
+// TODO: make it safe to call from NOFORK applets
+// Currently, it can exit(0). Even if it is made to do longjmp trick
+// (see sleep_and_die internals), zero cannot be passed thru this way!
+
 void fflush_stdout_and_exit(int retval)
 {
 	if (fflush(stdout))

libbb/make_directory.c

@@ -22,11 +22,10 @@
  * val.  Otherwise, pass -1 to get default permissions.
  */
 
-#include <errno.h>
-#include <unistd.h>
-#include <sys/stat.h>
 #include "libbb.h"
 
+/* This function is used from NOFORK applets. It must not allocate anything */
+
 int bb_make_directory (char *path, long mode, int flags)
 {
 	mode_t mask;

libbb/parse_mode.c

@@ -11,6 +11,8 @@
 
 #include "libbb.h"
 
+/* This function is used from NOFORK applets. It must not allocate anything */
+
 #define FILEMODEBITS (S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
 
 int bb_parse_mode(const char *s, mode_t *current_mode)

libbb/remove_file.c

@@ -9,6 +9,8 @@
 
 #include "libbb.h"
 
+/* Used from NOFORK applets. Must not allocate anything */
+
 int remove_file(const char *path, int flags)
 {
 	struct stat path_stat;