shell: fix SIGWINCH and SIGCHLD (in hush) interrupting line input, closes 15256

function                                             old     new   delta
record_pending_signo                                  32      63     +31
lineedit_read_key                                    231     224      -7
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 31/-7)              Total: 24 bytes

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

3 files changed, 20 insertions, 10 deletions

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index d6b2e76ff..b942f540a 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -2180,7 +2180,8 @@ static int lineedit_read_key(char *read_key_buffer, int timeout)
                  * "\xff\n",pause,"ls\n" invalid and thus won't lose "ls".
                  *
                  * If LI_INTERRUPTIBLE, return -1 if got EINTR in poll()
-                 * inside read_key, or if bb_got_signal != 0 (IOW: if signal
+                 * inside read_key and bb_got_signal became != 0,
+                 * or if bb_got_signal != 0 (IOW: if signal
                  * arrived before poll() is reached).
                  *
                  * Note: read_key sets errno to 0 on success.
@@ -2197,14 +2198,16 @@ static int lineedit_read_key(char *read_key_buffer, int timeout)
                         IF_FEATURE_EDITING_WINCH(S.ok_to_redraw = 0;)
                         if (errno != EINTR)
                                 break;
+                        /* It was EINTR. Repeat read_key() unless... */
                         if (state->flags & LI_INTERRUPTIBLE) {
-                                /* LI_INTERRUPTIBLE bails out on EINTR,
-                                 * but nothing really guarantees that bb_got_signal
-                                 * is nonzero. Follow the least surprise principle:
+                                /* LI_INTERRUPTIBLE bails out on EINTR
+                                 * if bb_got_signal became nonzero.
+                                 * (It may stay zero: for example, our SIGWINCH
+                                 * handler does not set it. This is used for signals
+                                 * which should not interrupt line editing).
                                  */
-                                if (bb_got_signal == 0)
-                                        bb_got_signal = 255;
-                                goto ret;
+                                if (bb_got_signal != 0)
+                                        goto ret; /* will return -1 */
                         }
                 }
 
diff --git a/shell/ash.c b/shell/ash.c
index 18ccc1329..5f8c8ea19 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -10821,7 +10821,8 @@ preadfd(void)
  again:
                 /* 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
+                 * getting EINTR in poll() and bb_got_signal became != 0,
+                 * or if it sees bb_got_signal != 0
                  * (IOW: if signal arrives before poll() is reached).
                  * Interactive testcases:
                  * (while kill -INT $$; do sleep 1; done) &
diff --git a/shell/hush.c b/shell/hush.c
index d111f0cc5..f064b8fd2 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -1946,7 +1946,12 @@ static void record_pending_signo(int sig)
 {
         sigaddset(&G.pending_set, sig);
 #if ENABLE_FEATURE_EDITING
-        bb_got_signal = sig; /* for read_line_input: "we got a signal" */
+        if (sig != SIGCHLD
+         || (G_traps && G_traps[SIGCHLD] && G_traps[SIGCHLD][0])
+         /* ^^^ if SIGCHLD, interrupt line reading only if it has a trap */
+        ) {
+                bb_got_signal = sig; /* for read_line_input: "we got a signal" */
+        }
 #endif
 #if ENABLE_HUSH_FAST
         if (sig == SIGCHLD) {
@@ -2669,7 +2674,8 @@ static int get_user_input(struct in_str *i)
                 } else {
                         /* For shell, LI_INTERRUPTIBLE is set:
                          * read_line_input will abort on either
-                         * getting EINTR in poll(), or if it sees bb_got_signal != 0
+                         * getting EINTR in poll() and bb_got_signal became != 0,
+                         * or if it sees bb_got_signal != 0
                          * (IOW: if signal arrives before poll() is reached).
                          * Interactive testcases:
                          * (while kill -INT $$; do sleep 1; done) &