hush: do not reset to default "" traps in subshell

function                                             old     new   delta
reset_traps_to_defaults                              164     211     +47
builtin_umask                                        123     121      -2

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

diff --git a/shell/hush.c b/shell/hush.c
index 00daf3ddd20e6c8e565af8fe82cd42d80766ba7b..d75b0da7e467e8f7bd204850ffa41081e4a41ba6 100644 (file)
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -1112,13 +1112,10 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  * are to count SIGCHLDs
  * and to restore tty pgrp on signal-induced exit.
  *
- * TODO compat:
+ * Note 2 (compat):
  * Standard says "When a subshell is entered, traps that are not being ignored
  * are set to the default actions". bash interprets it so that traps which
- * are set to "" (ignore) are NOT reset to defaults. We reset them to default.
- * bash example:
- * # trap '' SYS; (bash -c 'kill -SYS $PPID'; echo YES)
- * YES    <-- subshell was not killed by SIGSYS
+ * are set to "" (ignore) are NOT reset to defaults. We do the same.
  */
 enum {
        SPECIAL_INTERACTIVE_SIGS = 0
@@ -2605,43 +2602,51 @@ static void reset_traps_to_defaults(void)
 {
        /* This function is always called in a child shell
         * after fork (not vfork, NOMMU doesn't use this function).
-        * Child shells are not interactive.
-        * SIGTTIN/SIGTTOU/SIGTSTP should not have special handling.
-        * Testcase: (while :; do :; done) + ^Z should background.
-        * Same goes for SIGTERM, SIGHUP, SIGINT.
         */
        unsigned sig;
        unsigned mask;
 
+       /* Child shells are not interactive.
+        * SIGTTIN/SIGTTOU/SIGTSTP should not have special handling.
+        * Testcase: (while :; do :; done) + ^Z should background.
+        * Same goes for SIGTERM, SIGHUP, SIGINT.
+        */
        if (!G.traps && !(G.non_DFL_mask & SPECIAL_INTERACTIVE_SIGS))
-               return;
+               return; /* already no traps and no SPECIAL_INTERACTIVE_SIGS */
 
-       /* Stupid. It can be done with *single* &= op, but we can't use
-        * the fact that G.blocked_set is implemented as a bitmask... */
+       /* Switching off SPECIAL_INTERACTIVE_SIGS.
+        * Stupid. It can be done with *single* &= op, but we can't use
+        * the fact that G.blocked_set is implemented as a bitmask
+        * in libc... */
        mask = (SPECIAL_INTERACTIVE_SIGS >> 1);
        sig = 1;
        while (1) {
-               if (mask & 1)
-                       sigdelset(&G.blocked_set, sig);
+               if (mask & 1) {
+                       /* Careful. Only if no trap or trap is not "" */
+                       if (!G.traps || !G.traps[sig] || G.traps[sig][0])
+                               sigdelset(&G.blocked_set, sig);
+               }
                mask >>= 1;
                if (!mask)
                        break;
                sig++;
        }
-
+       /* Our homegrown sig mask is saner to work with :) */
        G.non_DFL_mask &= ~SPECIAL_INTERACTIVE_SIGS;
+
+       /* Resetting all traps to default except empty ones */
        mask = G.non_DFL_mask;
        if (G.traps) for (sig = 0; sig < NSIG; sig++, mask >>= 1) {
-               if (!G.traps[sig])
+               if (!G.traps[sig] || !G.traps[sig][0])
                        continue;
                free(G.traps[sig]);
                G.traps[sig] = NULL;
                /* There is no signal for 0 (EXIT) */
                if (sig == 0)
                        continue;
-               /* There was a trap handler, we are removing it.
+               /* There was a trap handler, we just removed it.
                 * But if sig still has non-DFL handling,
-                * we should not unblock it. */
+                * we should not unblock the sig. */
                if (mask & 1)
                        continue;
                sigdelset(&G.blocked_set, sig);

diff --git a/shell/hush_test/hush-trap/subshell.right b/shell/hush_test/hush-trap/subshell.right
new file mode 100644 (file)
index 0000000..0d20ed4
--- /dev/null
+++ b/shell/hush_test/hush-trap/subshell.right
@@ -0,0 +1,6 @@
+Ok
+Ok
+Ok
+Ok
+TERM
+Done

diff --git a/shell/hush_test/hush-trap/subshell.tests b/shell/hush_test/hush-trap/subshell.tests
new file mode 100755 (executable)
index 0000000..b5d6094
--- /dev/null
+++ b/shell/hush_test/hush-trap/subshell.tests
@@ -0,0 +1,20 @@
+# Non-empty traps should be reset in subshell
+
+# HUP is special in interactive shells
+trap '' HUP
+# QUIT is always special
+trap '' QUIT
+# SYS is not special
+trap '' SYS
+# WINCH is harmless
+trap 'bad: caught WINCH' WINCH
+# With TERM we'll check whether it is reset
+trap 'bad: caught TERM'  TERM
+
+# using bash, becuase we don't have $PPID (yet)
+(bash -c 'kill -HUP   $PPID'; echo Ok)
+(bash -c 'kill -QUIT  $PPID'; echo Ok)
+(bash -c 'kill -SYS   $PPID'; echo Ok)
+(bash -c 'kill -WINCH $PPID'; echo Ok)
+(bash -c 'kill -TERM  $PPID'; echo Bad: TERM is not reset)
+echo Done