hush: fix subshell.tests failure on NOMMU

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

3 files changed, 88 insertions, 41 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 7d851ed97..8de8d3c2a 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -520,6 +520,7 @@ struct globals {
         smalluint last_exitcode;
         /* are global_argv and global_argv[1..n] malloced? (note: not [0]) */
         smalluint global_args_malloced;
+        smalluint inherited_set_is_saved;
         /* how many non-NULL argv's we have. NB: $# + 1 */
         int global_argc;
         char **global_argv;
@@ -1050,7 +1051,8 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  *
  * Trap handlers will execute even within trap handlers. (right?)
  *
- * User trap handlers are forgotten when subshell ("(cmd)") is entered.
+ * User trap handlers are forgotten when subshell ("(cmd)") is entered,
+ * except for handlers set to '' (empty string).
  *
  * If job control is off, backgrounded commands ("cmd &")
  * have SIGINT, SIGQUIT set to SIG_IGN.
@@ -1106,7 +1108,7 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  * after [v]fork, if we plan to be a shell:
  *    unblock signals with special interactive handling
  *    (child shell is not interactive),
- *    unset all traps (note: regardless of child shell's type - {}, (), etc)
+ *    unset all traps except '' (note: regardless of child shell's type - {}, (), etc)
  * after [v]fork, if we plan to exec:
  *    POSIX says fork clears pending signal mask in child - no need to clear it.
  *    Restore blocked signal set to one inherited by shell just prior to exec.
@@ -1118,7 +1120,7 @@ static void restore_G_args(save_arg_t *sv, char **argv)
  * 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 do the same.
+ * are set to '' (ignore) are NOT reset to defaults. We do the same.
  */
 enum {
         SPECIAL_INTERACTIVE_SIGS = 0
@@ -2925,6 +2927,7 @@ static void re_execute_shell(char ***to_free, const char *s,
 # endif
         char **argv, **pp;
         unsigned cnt;
+        unsigned long long empty_trap_mask;
 
         if (!g_argv0) { /* heredoc */
                 argv = heredoc_argv;
@@ -2941,12 +2944,22 @@ static void re_execute_shell(char ***to_free, const char *s,
         if (pp) while (*pp++)
                 cnt++;
 
-        sprintf(param_buf, "-$%x:%x:%x:%x:%x" IF_HUSH_LOOPS(":%x")
+        empty_trap_mask = 0;
+        if (G.traps) {
+                int sig;
+                for (sig = 1; sig < NSIG; sig++) {
+                        if (G.traps[sig] && !G.traps[sig][0])
+                                empty_trap_mask |= 1LL << sig;
+                }
+        }
+
+        sprintf(param_buf, "-$%x:%x:%x:%x:%x:%llx" IF_HUSH_LOOPS(":%x")
                         , (unsigned) G.root_pid
                         , (unsigned) G.root_ppid
                         , (unsigned) G.last_bg_pid
                         , (unsigned) G.last_exitcode
                         , cnt
+                        , empty_trap_mask
                         IF_HUSH_LOOPS(, G.depth_of_loop)
                         );
         /* 1:hush 2:-$<pid>:<pid>:<exitcode>:<depth> <vars...> <funcs...>
@@ -3002,7 +3015,9 @@ static void re_execute_shell(char ***to_free, const char *s,
          * _inside_ group (just before echo 1), it works.
          *
          * I conclude it means we don't need to pass active traps here.
-         * exec syscall below resets them to SIG_DFL for us.
+         * Even if we would use signal handlers instead of signal masking
+         * in order to implement trap handling,
+         * exec syscall below resets signals to SIG_DFL for us.
          */
         *pp++ = (char *) "-c";
         *pp++ = (char *) s;
@@ -5447,7 +5462,7 @@ static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
         pid_t pid;
         int channel[2];
 # if !BB_MMU
-        char **to_free;
+        char **to_free = NULL;
 # endif
 
         xpipe(channel);
@@ -6677,10 +6692,17 @@ static void parse_and_run_file(FILE *f)
 }
 
 /* Called a few times only (or even once if "sh -c") */
-static void block_signals(int second_time)
+static void init_sigmasks(void)
 {
         unsigned sig;
         unsigned mask;
+        sigset_t old_blocked_set;
+
+        if (!G.inherited_set_is_saved) {
+                sigprocmask(SIG_SETMASK, NULL, &G.blocked_set);
+                G.inherited_set = G.blocked_set;
+        }
+        old_blocked_set = G.blocked_set;
 
         mask = (1 << SIGQUIT);
         if (G_interactive_fd) {
@@ -6690,8 +6712,6 @@ static void block_signals(int second_time)
         }
         G.non_DFL_mask = mask;
 
-        if (!second_time)
-                sigprocmask(SIG_SETMASK, NULL, &G.blocked_set);
         sig = 0;
         while (mask) {
                 if (mask & 1)
@@ -6701,18 +6721,21 @@ static void block_signals(int second_time)
         }
         sigdelset(&G.blocked_set, SIGCHLD);
 
-        sigprocmask(SIG_SETMASK, &G.blocked_set,
-                        second_time ? NULL : &G.inherited_set);
+        if (memcmp(&old_blocked_set, &G.blocked_set, sizeof(old_blocked_set)) != 0)
+                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
+
         /* POSIX allows shell to re-enable SIGCHLD
          * even if it was SIG_IGN on entry */
 #if ENABLE_HUSH_FAST
         G.count_SIGCHLD++; /* ensure it is != G.handled_SIGCHLD */
-        if (!second_time)
+        if (!G.inherited_set_is_saved)
                 signal(SIGCHLD, SIGCHLD_handler);
 #else
-        if (!second_time)
+        if (!G.inherited_set_is_saved)
                 signal(SIGCHLD, SIG_DFL);
 #endif
+
+        G.inherited_set_is_saved = 1;
 }
 
 #if ENABLE_HUSH_JOB
@@ -6774,7 +6797,6 @@ int hush_main(int argc, char **argv)
                 .flg_export = 1,
                 .flg_read_only = 1,
         };
-        int signal_mask_is_inited = 0;
         int opt;
         unsigned builtin_argc;
         char **e;
@@ -6865,10 +6887,9 @@ int hush_main(int argc, char **argv)
         }
 
         /* Shell is non-interactive at first. We need to call
-         * block_signals(0) if we are going to execute "sh <script>",
+         * init_sigmasks() if we are going to execute "sh <script>",
          * "sh -c <cmds>" or login shell's /etc/profile and friends.
-         * If we later decide that we are interactive, we run block_signals(0)
-         * (or re-run block_signals(1) if we ran block_signals(0) before)
+         * If we later decide that we are interactive, we run init_sigmasks()
          * in order to intercept (more) signals.
          */
 
@@ -6908,7 +6929,7 @@ int hush_main(int argc, char **argv)
                                 /* -c 'builtin' [BARGV...] "" ARG0 [ARG1...] */
                                 const struct built_in_command *x;
 
-                                block_signals(0); /* 0: called 1st time */
+                                init_sigmasks();
                                 x = find_builtin(optarg);
                                 if (x) { /* paranoia */
                                         G.global_argc -= builtin_argc; /* skip [BARGV...] "" */
@@ -6924,7 +6945,7 @@ int hush_main(int argc, char **argv)
                                 G.global_argv[0] = argv[0];
                                 G.global_argc--;
                         } /* else -c 'script' ARG0 [ARG1...]: $0 is ARG0 */
-                        block_signals(0); /* 0: called 1st time */
+                        init_sigmasks();
                         parse_and_run_string(optarg);
                         goto final_return;
                 case 'i':
@@ -6940,7 +6961,9 @@ int hush_main(int argc, char **argv)
                 case '<': /* "big heredoc" support */
                         full_write(STDOUT_FILENO, optarg, strlen(optarg));
                         _exit(0);
-                case '$':
+                case '$': {
+                        unsigned long long empty_trap_mask;
+
                         G.root_pid = bb_strtou(optarg, &optarg, 16);
                         optarg++;
                         G.root_ppid = bb_strtou(optarg, &optarg, 16);
@@ -6950,11 +6973,26 @@ int hush_main(int argc, char **argv)
                         G.last_exitcode = bb_strtou(optarg, &optarg, 16);
                         optarg++;
                         builtin_argc = bb_strtou(optarg, &optarg, 16);
+                        optarg++;
+                        empty_trap_mask = bb_strtoull(optarg, &optarg, 16);
+                        if (empty_trap_mask != 0) {
+                                int sig;
+                                init_sigmasks();
+                                G.traps = xzalloc(sizeof(G.traps[0]) * NSIG);
+                                for (sig = 1; sig < NSIG; sig++) {
+                                        if (empty_trap_mask & (1LL << sig)) {
+                                                G.traps[sig] = xzalloc(1); /* == xstrdup(""); */
+                                                sigaddset(&G.blocked_set, sig);
+                                        }
+                                }
+                                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
+                        }
 # if ENABLE_HUSH_LOOPS
                         optarg++;
                         G.depth_of_loop = bb_strtou(optarg, &optarg, 16);
 # endif
                         break;
+                }
                 case 'R':
                 case 'V':
                         set_local_var(xstrdup(optarg), /*exp:*/ 0, /*lvl:*/ 0, /*ro:*/ opt == 'R');
@@ -6997,8 +7035,7 @@ int hush_main(int argc, char **argv)
                 input = fopen_for_read("/etc/profile");
                 if (input != NULL) {
                         close_on_exec_on(fileno(input));
-                        block_signals(0); /* 0: called 1st time */
-                        signal_mask_is_inited = 1;
+                        init_sigmasks();
                         parse_and_run_file(input);
                         fclose(input);
                 }
@@ -7023,8 +7060,7 @@ int hush_main(int argc, char **argv)
                 G.global_argc = argc - optind;
                 input = xfopen_for_read(argv[optind]);
                 close_on_exec_on(fileno(input));
-                if (!signal_mask_is_inited)
-                        block_signals(0); /* 0: called 1st time */
+                init_sigmasks();
                 parse_and_run_file(input);
 #if ENABLE_FEATURE_CLEAN_UP
                 fclose(input);
@@ -7033,7 +7069,7 @@ int hush_main(int argc, char **argv)
         }
 
         /* Up to here, shell was non-interactive. Now it may become one.
-         * NB: don't forget to (re)run block_signals(0/1) as needed.
+         * NB: don't forget to (re)run init_sigmasks() as needed.
          */
 
         /* A shell is interactive if the '-i' flag was given,
@@ -7086,7 +7122,7 @@ int hush_main(int argc, char **argv)
                 }
 
                 /* Block some signals */
-                block_signals(signal_mask_is_inited);
+                init_sigmasks();
 
                 if (G_saved_tty_pgrp) {
                         /* Set other signals to restore saved_tty_pgrp */
@@ -7100,9 +7136,9 @@ int hush_main(int argc, char **argv)
                 /* -1 is special - makes xfuncs longjmp, not exit
                  * (we reset die_sleep = 0 whereever we [v]fork) */
                 enable_restore_tty_pgrp_on_exit(); /* sets die_sleep = -1 */
-        } else if (!signal_mask_is_inited) {
-                block_signals(0); /* 0: called 1st time */
-        } /* else: block_signals(0) was done before */
+        } else {
+                init_sigmasks();
+        }
 #elif ENABLE_HUSH_INTERACTIVE
         /* No job control compiled in, only prompt/line editing */
         if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)) {
@@ -7117,15 +7153,11 @@ int hush_main(int argc, char **argv)
         }
         if (G_interactive_fd) {
                 close_on_exec_on(G_interactive_fd);
-                block_signals(signal_mask_is_inited);
-        } else if (!signal_mask_is_inited) {
-                block_signals(0);
         }
+        init_sigmasks();
 #else
         /* We have interactiveness code disabled */
-        if (!signal_mask_is_inited) {
-                block_signals(0);
-        }
+        init_sigmasks();
 #endif
         /* bash:
          * if interactive but not a login shell, sources ~/.bashrc
@@ -7471,7 +7503,7 @@ static int FAST_FUNC builtin_trap(char **argv)
                         free(G.traps[sig]);
                         G.traps[sig] = xstrdup(new_cmd);
 
-                        debug_printf("trap: setting SIG%s (%i) to '%s'",
+                        debug_printf("trap: setting SIG%s (%i) to '%s'\n",
                                 get_signame(sig), sig, G.traps[sig]);
 
                         /* There is no signal for 0 (EXIT) */
diff --git a/shell/hush_test/hush-trap/subshell.right b/shell/hush_test/hush-trap/subshell.right
index 0d20ed4e9..f865b932b 100644
--- a/shell/hush_test/hush-trap/subshell.right
+++ b/shell/hush_test/hush-trap/subshell.right
@@ -1,6 +1,21 @@
+trap -- '' HUP
+trap -- '' QUIT
+trap -- '' SYS
 Ok
+trap -- '' HUP
+trap -- '' QUIT
+trap -- '' SYS
 Ok
+trap -- '' HUP
+trap -- '' QUIT
+trap -- '' SYS
 Ok
+trap -- '' HUP
+trap -- '' QUIT
+trap -- '' SYS
 Ok
+trap -- '' HUP
+trap -- '' QUIT
+trap -- '' SYS
 TERM
 Done
diff --git a/shell/hush_test/hush-trap/subshell.tests b/shell/hush_test/hush-trap/subshell.tests
index 4564c2ee2..045294bf4 100755
--- a/shell/hush_test/hush-trap/subshell.tests
+++ b/shell/hush_test/hush-trap/subshell.tests
@@ -12,9 +12,9 @@ trap 'bad: caught WINCH' WINCH
 trap 'bad: caught TERM'  TERM
 
 # using bash, because 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)
+(trap; bash -c 'kill -HUP   $PPID'; echo Ok)
+(trap; bash -c 'kill -QUIT  $PPID'; echo Ok)
+(trap; bash -c 'kill -SYS   $PPID'; echo Ok)
+(trap; bash -c 'kill -WINCH $PPID'; echo Ok)
+(trap; bash -c 'kill -TERM  $PPID'; echo Bad: TERM is not reset)
 echo Done