ash,hush: fix handling of SIGINT while waiting for interactive input

function                                             old     new   delta
lineedit_read_key                                    160     237     +77
__pgetc                                              522     589     +67
fgetc_interactive                                    244     309     +65
safe_read_key                                          -      39     +39
read_key                                             588     607     +19
record_pending_signo                                  23      32      +9
signal_handler                                        75      81      +6
.rodata                                           104312  104309      -3
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 6/1 up/down: 282/-3)            Total: 279 bytes

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

2 files changed, 77 insertions, 29 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 086773dd7..55df54bd0 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -3679,7 +3679,9 @@ signal_handler(int signo)
 		if (!trap[SIGCHLD])
 			return;
 	}
-
+#if ENABLE_FEATURE_EDITING
+	bb_got_signal = signo; /* for read_line_input: "we got a signal" */
+#endif
 	gotsig[signo - 1] = 1;
 	pending_sig = signo;
 
@@ -10784,33 +10786,52 @@ preadfd(void)
 # endif
 		reinit_unicode_for_ash();
  again:
-//BUG: not in INT_OFF/INT_ON section - SIGINT et al would longjmp out of read_line_input()!
-//This would cause a memory leak in interactive shell
-//(repeated internal allocations in read_line_input):
-// (while kill -INT $$; do :; done) &
+		/* For shell, LI_INTERRUPTIBLE is set:
+		 * read_line_input will abort on either
+		 * getting EINTR in poll(), or if it sees bb_got_signal != 0
+		 * (IOW: if signal arrives before poll() is reached).
+		 * Interactive testcases:
+		 * (while kill -INT $$; do sleep 1; done) &
+		 * #^^^ prints ^C, prints prompt, repeats
+		 * trap 'echo I' int; (while kill -INT $$; do sleep 1; done) &
+		 * #^^^ prints ^C, prints "I", prints prompt, repeats
+		 * trap 'echo T' term; (while kill $$; do sleep 1; done) &
+		 * #^^^ prints "T", prints prompt, repeats
+		 * #(bash 5.0.17 exits after first "T", looks like a bug)
+		 */
+		bb_got_signal = 0;
+		INT_OFF; /* no longjmp'ing out of read_line_input please */
 		nr = read_line_input(line_input_state, cmdedit_prompt, buf, IBUFSIZ);
+		if (bb_got_signal == SIGINT)
+			write(STDOUT_FILENO, "^C\n", 3);
+		INT_ON; /* here non-blocked SIGINT will longjmp */
 		if (nr == 0) {
 			/* ^C pressed, "convert" to SIGINT */
-			write(STDOUT_FILENO, "^C", 2);
-			raise(SIGINT);
+			write(STDOUT_FILENO, "^C\n", 3);
+			raise(SIGINT); /* here non-blocked SIGINT will longjmp */
 			/* raise(SIGINT) did not work! (e.g. if SIGINT
 			 * is SIG_IGNed on startup, it stays SIG_IGNed)
 			 */
 			if (trap[SIGINT]) {
+ empty_line_input:
 				buf[0] = '\n';
 				buf[1] = '\0';
 				return 1;
 			}
 			exitstatus = 128 + SIGINT;
 			/* bash behavior on ^C + ignored SIGINT: */
-			write(STDOUT_FILENO, "\n", 1);
 			goto again;
 		}
 		if (nr < 0) {
 			if (errno == 0) {
-				/* Ctrl+D pressed */
+				/* ^D pressed */
 				nr = 0;
 			}
+			else if (errno == EINTR) { /* got signal? */
+				if (bb_got_signal != SIGINT)
+					write(STDOUT_FILENO, "\n", 1);
+				goto empty_line_input;
+			}
 # if ENABLE_ASH_IDLE_TIMEOUT
 			else if (errno == EAGAIN && timeout > 0) {
 				puts("\007timed out waiting for input: auto-logout");
diff --git a/shell/hush.c b/shell/hush.c
index 7d0dc67e4..6dc2ecaac 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -918,6 +918,7 @@ struct globals {
 #if ENABLE_HUSH_INTERACTIVE
 	smallint promptmode; /* 0: PS1, 1: PS2 */
 #endif
+	/* set by signal handler if SIGINT is received _and_ its trap is not set */
 	smallint flag_SIGINT;
 #if ENABLE_HUSH_LOOPS
 	smallint flag_break_continue;
@@ -1944,6 +1945,9 @@ enum {
 static void record_pending_signo(int sig)
 {
 	sigaddset(&G.pending_set, sig);
+#if ENABLE_FEATURE_EDITING
+	bb_got_signal = sig; /* for read_line_input: "we got a signal" */
+#endif
 #if ENABLE_HUSH_FAST
 	if (sig == SIGCHLD) {
 		G.count_SIGCHLD++;
@@ -2652,30 +2656,53 @@ static int get_user_input(struct in_str *i)
 	for (;;) {
 		reinit_unicode_for_hush();
 		G.flag_SIGINT = 0;
-		/* buglet: SIGINT will not make new prompt to appear _at once_,
-		 * only after <Enter>. (^C works immediately) */
-		r = read_line_input(G.line_input_state, prompt_str,
+
+		bb_got_signal = 0;
+		if (!sigisemptyset(&G.pending_set)) {
+			/* Whoops, already got a signal, do not call read_line_input */
+			bb_got_signal = r = -1;
+		} else {
+			/* For shell, LI_INTERRUPTIBLE is set:
+			 * read_line_input will abort on either
+			 * getting EINTR in poll(), or if it sees bb_got_signal != 0
+			 * (IOW: if signal arrives before poll() is reached).
+			 * Interactive testcases:
+			 * (while kill -INT $$; do sleep 1; done) &
+			 * #^^^ prints ^C, prints prompt, repeats
+			 * trap 'echo I' int; (while kill -INT $$; do sleep 1; done) &
+			 * #^^^ prints ^C, prints "I", prints prompt, repeats
+			 * trap 'echo T' term; (while kill $$; do sleep 1; done) &
+			 * #^^^ prints "T", prints prompt, repeats
+			 * #(bash 5.0.17 exits after first "T", looks like a bug)
+			 */
+			r = read_line_input(G.line_input_state, prompt_str,
 				G.user_input_buf, CONFIG_FEATURE_EDITING_MAX_LEN-1
-		);
-		/* read_line_input intercepts ^C, "convert" it to SIGINT */
-		if (r == 0) {
-			raise(SIGINT);
+			);
+			/* read_line_input intercepts ^C, "convert" it to SIGINT */
+			if (r == 0)
+				raise(SIGINT);
+		}
+		/* bash prints ^C (before running a trap, if any)
+		 * both on keyboard ^C and on real SIGINT (non-kbd generated).
+		 */
+		if (sigismember(&G.pending_set, SIGINT)) {
+			write(STDOUT_FILENO, "^C\n", 3);
+			G.last_exitcode = 128 | SIGINT;
 		}
 		check_and_run_traps();
-		if (r != 0 && !G.flag_SIGINT)
+		if (r == 0) /* keyboard ^C? */
+			continue; /* go back, read another input line */
+		if (r > 0) /* normal input? (no ^C, no ^D, no signals) */
 			break;
-		/* ^C or SIGINT: repeat */
-		/* bash prints ^C even on real SIGINT (non-kbd generated) */
-		write(STDOUT_FILENO, "^C\n", 3);
-		G.last_exitcode = 128 | SIGINT;
-	}
-	if (r < 0) {
-		/* EOF/error detected */
-		/* ^D on interactive input goes to next line before exiting: */
-		write(STDOUT_FILENO, "\n", 1);
-		i->p = NULL;
-		i->peek_buf[0] = r = EOF;
-		return r;
+		if (!bb_got_signal) {
+			/* r < 0: ^D/EOF/error detected (but not signal) */
+			/* ^D on interactive input goes to next line before exiting: */
+			write(STDOUT_FILENO, "\n", 1);
+			i->p = NULL;
+			i->peek_buf[0] = r = EOF;
+			return r;
+		}
+		/* it was a signal: go back, read another input line */
 	}
 	i->p = G.user_input_buf;
 	return (unsigned char)*i->p++;