ash,hush: add comment about masked SIGCHLD, handle SIG_IGNed SIGHUP as in bash

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

2 files changed, 37 insertions, 9 deletions

diff --git a/shell/ash.c b/shell/ash.c
index ff594050c..fea4b10a7 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -4307,8 +4307,19 @@ wait_block_or_sig(int *status)
 #if 1
                 sigfillset(&mask);
                 sigprocmask2(SIG_SETMASK, &mask); /* mask is updated */
-                while (!got_sigchld && !pending_sig)
+                while (!got_sigchld && !pending_sig) {
                         sigsuspend(&mask);
+                        /* ^^^ add "sigdelset(&mask, SIGCHLD);" before sigsuspend
+                         * to make sure SIGCHLD is not masked off?
+                         * It was reported that this:
+                         *      fn() { : | return; }
+                         *      shopt -s lastpipe
+                         *      fn
+                         *      exec ash SCRIPT
+                         * under bash 4.4.23 runs SCRIPT with SIGCHLD masked,
+                         * making "wait" commands in SCRIPT block forever.
+                         */
+                }
                 sigprocmask(SIG_SETMASK, &mask, NULL);
 #else /* unsafe: a signal can set pending_sig after check, but before pause() */
                 while (!got_sigchld && !pending_sig)
@@ -14170,11 +14181,6 @@ init(void)
         sigmode[SIGCHLD - 1] = S_DFL; /* ensure we install handler even if it is SIG_IGNed */
         setsignal(SIGCHLD);
 
-        /* bash re-enables SIGHUP which is SIG_IGNed on entry.
-         * Try: "trap '' HUP; bash; echo RET" and type "kill -HUP $$"
-         */
-        signal(SIGHUP, SIG_DFL);
-
         {
                 char **envp;
                 const char *p;
@@ -14512,6 +14518,14 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
                 }
 #endif
  state4: /* XXX ??? - why isn't this before the "if" statement */
+
+                /* Interactive bash re-enables SIGHUP which is SIG_IGNed on entry.
+                 * Try:
+                 * trap '' hup; bash; echo RET  # type "kill -hup $$", see SIGHUP having effect
+                 * trap '' hup; bash -c 'kill -hup $$; echo ALIVE'  # here SIGHUP is SIG_IGNed
+                 */
+                signal(SIGHUP, SIG_DFL);
+
                 cmdloop(1);
         }
 #if PROFILE
diff --git a/shell/hush.c b/shell/hush.c
index 6e44d4e11..bced388bf 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -9775,10 +9775,14 @@ static void install_sighandlers(unsigned mask)
                  */
                 if (sig == SIGCHLD)
                         continue;
-                /* bash re-enables SIGHUP which is SIG_IGNed on entry.
-                 * Try: "trap '' HUP; bash; echo RET" and type "kill -HUP $$"
+                /* Interactive bash re-enables SIGHUP which is SIG_IGNed on entry.
+                 * Try:
+                 * trap '' hup; bash; echo RET  # type "kill -hup $$", see SIGHUP having effect
+                 * trap '' hup; bash -c 'kill -hup $$; echo ALIVE'  # here SIGHUP is SIG_IGNed
                  */
-                //if (sig == SIGHUP) continue; - TODO?
+                if (sig == SIGHUP && G_interactive_fd)
+                        continue;
+                /* Unless one of the above signals, is it SIG_IGN? */
                 if (old_handler == SIG_IGN) {
                         /* oops... restore back to IGN, and record this fact */
                         install_sighandler(sig, old_handler);
@@ -11554,6 +11558,16 @@ static int wait_for_child_or_signal(struct pipe *waitfor_pipe, pid_t waitfor_pid
                 /* It is vitally important for sigsuspend that SIGCHLD has non-DFL handler! */
                 /* Note: sigsuspend invokes signal handler */
                 sigsuspend(&oldset);
+                /* ^^^ add "sigdelset(&oldset, SIGCHLD)" before sigsuspend
+                 * to make sure SIGCHLD is not masked off?
+                 * It was reported that this:
+                 *      fn() { : | return; }
+                 *      shopt -s lastpipe
+                 *      fn
+                 *      exec hush SCRIPT
+                 * under bash 4.4.23 runs SCRIPT with SIGCHLD masked,
+                 * making "wait" commands in SCRIPT block forever.
+                 */
  restore:
                 sigprocmask(SIG_SETMASK, &oldset, NULL);
  check_sig: