NOFORK fixes

"rm -i FILE" and "yes" can now be interrupted by ^C in hush.
This also now works:

$ usleep 19999999
^C
$ echo $?
130

function                                             old     new   delta
run_pipe                                            1668    1711     +43
pseudo_exec_argv                                     312     321      +9
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 52/0)               Total: 52 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 48 insertions, 6 deletions

diff --git a/coreutils/rm.c b/coreutils/rm.c
index f91c94570..5e4acab8c 100644
--- a/coreutils/rm.c
+++ b/coreutils/rm.c
@@ -16,7 +16,8 @@
 //config:	help
 //config:	rm is used to remove files or directories.
 
-//applet:IF_RM(APPLET_NOFORK(rm, rm, BB_DIR_BIN, BB_SUID_DROP, rm))
+//applet:IF_RM(APPLET_NOEXEC(rm, rm, BB_DIR_BIN, BB_SUID_DROP, rm))
+/* was NOFORK, but then "rm -i FILE" can't be ^C'ed if run by hush */
 
 //kbuild:lib-$(CONFIG_RM) += rm.o
 
@@ -36,7 +37,7 @@
 
 #include "libbb.h"
 
-/* This is a NOFORK applet. Be very careful! */
+/* This is a NOEXEC applet. Be very careful! */
 
 int rm_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int rm_main(int argc UNUSED_PARAM, char **argv)
diff --git a/coreutils/seq.c b/coreutils/seq.c
index f36dbb4ec..c26ff06b9 100644
--- a/coreutils/seq.c
+++ b/coreutils/seq.c
@@ -12,7 +12,8 @@
 //config:	help
 //config:	print a sequence of numbers
 
-//applet:IF_SEQ(APPLET_NOFORK(seq, seq, BB_DIR_USR_BIN, BB_SUID_DROP, seq))
+//applet:IF_SEQ(APPLET_NOEXEC(seq, seq, BB_DIR_USR_BIN, BB_SUID_DROP, seq))
+/* was NOFORK, but then "seq 1 999999999" can't be ^C'ed if run by hush */
 
 //kbuild:lib-$(CONFIG_SEQ) += seq.o
 
@@ -26,7 +27,7 @@
 
 #include "libbb.h"
 
-/* This is a NOFORK applet. Be very careful! */
+/* This is a NOEXEC applet. Be very careful! */
 
 int seq_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int seq_main(int argc, char **argv)
diff --git a/coreutils/usleep.c b/coreutils/usleep.c
index 7c25aada1..684ab781b 100644
--- a/coreutils/usleep.c
+++ b/coreutils/usleep.c
@@ -38,6 +38,13 @@ int usleep_main(int argc UNUSED_PARAM, char **argv)
 		bb_show_usage();
 	}
 
+	/* Safe wrt NOFORK? (noforks are not allowed to run for
+	 * a long time). Try "usleep 99999999" + ^C + "echo $?"
+	 * in hush with FEATURE_SH_NOFORK=y.
+	 * At least on uclibc, usleep() thanslates to nanosleep()
+	 * which returns early on any signal (even caught one),
+	 * and uclibc does not loop back on EINTR.
+	 */
 	usleep(xatou(argv[1]));
 
 	return EXIT_SUCCESS;
diff --git a/coreutils/yes.c b/coreutils/yes.c
index ea35d146c..c244bfe10 100644
--- a/coreutils/yes.c
+++ b/coreutils/yes.c
@@ -17,7 +17,8 @@
 //config:	yes is used to repeatedly output a specific string, or
 //config:	the default string 'y'.
 
-//applet:IF_YES(APPLET_NOFORK(yes, yes, BB_DIR_USR_BIN, BB_SUID_DROP, yes))
+//applet:IF_YES(APPLET_NOEXEC(yes, yes, BB_DIR_USR_BIN, BB_SUID_DROP, yes))
+/* was NOFORK, but then yes can't be ^C'ed if run by hush */
 
 //kbuild:lib-$(CONFIG_YES) += yes.o
 
diff --git a/docs/nofork_noexec.txt b/docs/nofork_noexec.txt
index a24dd9c27..0ad4e6e60 100644
--- a/docs/nofork_noexec.txt
+++ b/docs/nofork_noexec.txt
@@ -52,6 +52,9 @@ xargs, find, shells do it (grep for "spawn_and_wait" and
 This poses much more serious limitations on what applet can do:
 
 * all NOEXEC limitations apply.
+* do not run for a long time or wait for user input:
+  hush shell only handles signals (like ^C) after you return
+  from APPLET_main().
 * do not ever exit() or exec().
   - xfuncs are okay. They are using special trick to return
     to the caller applet instead of dying when they detect "x" condition.
diff --git a/shell/hush.c b/shell/hush.c
index 9f946d82f..cfefb7324 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -7363,6 +7363,8 @@ static NOINLINE void pseudo_exec_argv(nommu_save_t *nommu_save,
 				 */
 				close_saved_fds_and_FILE_fds();
 //FIXME: should also close saved redir fds
+				/* Without this, "rm -i FILE" can't be ^C'ed: */
+				switch_off_special_sigs(G.special_sig_mask);
 				debug_printf_exec("running applet '%s'\n", argv[0]);
 				run_applet_no_and_exit(a, argv[0], argv);
 			}
@@ -8045,6 +8047,24 @@ static NOINLINE int run_pipe(struct pipe *pi)
 			add_vars(old_vars);
 /* clean_up_and_ret0: */
 			restore_redirects(squirrel);
+			/*
+			 * Try "usleep 99999999" + ^C + "echo $?"
+			 * with FEATURE_SH_NOFORK=y.
+			 */
+			if (!funcp) {
+				/* It was builtin or nofork.
+				 * if this would be a real fork/execed program,
+				 * it should have died if a fatal sig was received.
+				 * But OTOH, there was no separate process,
+				 * the sig was sent to _shell_, not to non-existing
+				 * child.
+				 * Let's just handle ^C only, this one is obvious:
+				 * we aren't ok with exitcode 0 when ^C was pressed
+				 * during builtin/nofork.
+				 */
+				if (sigismember(&G.pending_set, SIGINT))
+					rcode = 128 + SIGINT;
+			}
  clean_up_and_ret1:
 			free(argv_expanded);
 			IF_HAS_KEYWORDS(if (pi->pi_inverted) rcode = !rcode;)
@@ -8060,6 +8080,14 @@ static NOINLINE int run_pipe(struct pipe *pi)
 				if (rcode == 0) {
 					debug_printf_exec(": run_nofork_applet '%s' '%s'...\n",
 						argv_expanded[0], argv_expanded[1]);
+					/*
+					 * Note: signals (^C) can't interrupt here.
+					 * We remember them and they will be acted upon
+					 * after applet returns.
+					 * This makes applets which can run for a long time
+					 * and/or wait for user input ineligible for NOFORK:
+					 * for example, "yes" or "rm" (rm -i waits for input).
+					 */
 					rcode = run_nofork_applet(n, argv_expanded);
 				}
 				goto clean_up_and_ret;
@@ -8491,7 +8519,7 @@ static int run_list(struct pipe *pi)
 			G.last_bg_pid = pi->cmds[pi->num_cmds - 1].pid;
 			G.last_bg_pid_exitcode = 0;
 			debug_printf_exec(": cmd&: exitcode EXIT_SUCCESS\n");
-/* Check pi->pi_inverted? "! sleep 1 & echo $?": bash says 1. dash and ash says 0 */
+/* Check pi->pi_inverted? "! sleep 1 & echo $?": bash says 1. dash and ash say 0 */
 			rcode = EXIT_SUCCESS;
 			goto check_traps;
 		} else {
@@ -10178,6 +10206,7 @@ static int wait_for_child_or_signal(struct pipe *waitfor_pipe, pid_t waitfor_pid
 		/* So, did we get a signal? */
 		sig = check_and_run_traps();
 		if (sig /*&& sig != SIGCHLD - always true */) {
+			/* Do this for any (non-ignored) signal, not only for ^C */
 			ret = 128 + sig;
 			break;
 		}