ash: fix var_leak.tests so that it actually catches the NOFORK bug

+ document the bug better

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

3 files changed, 21 insertions, 9 deletions

diff --git a/shell/ash.c b/shell/ash.c
index d082333ba..83886c610 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -9179,12 +9179,14 @@ evalcommand(union node *cmd, int flags)
 
         /* Execute the command. */
         switch (cmdentry.cmdtype) {
-        default:
+        default: {
 
 #if ENABLE_FEATURE_SH_NOFORK
-/* Hmmm... shouldn't it happen somewhere in forkshell() instead?
- * Why "fork off a child process if necessary" doesn't apply to NOFORK? */
-        {
+/* (1) BUG: if variables are set, we need to fork, or save/restore them
+ *     around run_nofork_applet() call.
+ * (2) Should this check also be done in forkshell()?
+ *     (perhaps it should, so that "VAR=VAL nofork" at least avoids exec...)
+ */
                 /* find_command() encodes applet_no as (-2 - applet_no) */
                 int applet_no = (- cmdentry.u.index - 2);
                 if (applet_no >= 0 && APPLET_IS_NOFORK(applet_no)) {
@@ -9193,10 +9195,13 @@ evalcommand(union node *cmd, int flags)
                         exitstatus = run_nofork_applet(applet_no, argv);
                         break;
                 }
-        }
 #endif
-                /* Fork off a child process if necessary. */
+                /* Can we avoid forking off? For example, very last command
+                 * in a script or a subshell does not need forking,
+                 * we can just exec it.
+                 */
                 if (!(flags & EV_EXIT) || may_have_traps) {
+                        /* No, forking off a child is necessary */
                         INT_OFF;
                         jp = makejob(/*cmd,*/ 1);
                         if (forkshell(jp, cmd, FORK_FG) != 0) {
@@ -9213,7 +9218,7 @@ evalcommand(union node *cmd, int flags)
                 listsetvar(varlist.list, VEXPORT|VSTACK);
                 shellexec(argv, path, cmdentry.u.index);
                 /* NOTREACHED */
-
+        } /* default */
         case CMDBUILTIN:
                 cmdenviron = varlist.list;
                 if (cmdenviron) {
@@ -9258,7 +9263,8 @@ evalcommand(union node *cmd, int flags)
                 if (evalfun(cmdentry.u.func, argc, argv, flags))
                         goto raise;
                 break;
-        }
+
+        } /* switch */
 
  out:
         popredir(/*drop:*/ cmd_is_exec, /*restore:*/ cmd_is_exec);
diff --git a/shell/ash_test/ash-vars/var_leak.right b/shell/ash_test/ash-vars/var_leak.right
index be78112c8..01a5e3263 100644
--- a/shell/ash_test/ash-vars/var_leak.right
+++ b/shell/ash_test/ash-vars/var_leak.right
@@ -1,3 +1,4 @@
 should be empty: ''
+should be empty: ''
 should be not empty: 'val2'
 should be not empty: 'val3'
diff --git a/shell/ash_test/ash-vars/var_leak.tests b/shell/ash_test/ash-vars/var_leak.tests
index 032059295..5242e24eb 100755
--- a/shell/ash_test/ash-vars/var_leak.tests
+++ b/shell/ash_test/ash-vars/var_leak.tests
@@ -1,6 +1,11 @@
-# true is a regular builtin, varibale should not leak out of it
+# cat is an external program, variable should not leak out of it.
 # this currently fails with CONFIG_FEATURE_SH_NOFORK=y
 VAR=''
+VAR=val0 cat /dev/null
+echo "should be empty: '$VAR'"
+
+# true is a regular builtin, variable should not leak out of it.
+VAR=''
 VAR=val1 true
 echo "should be empty: '$VAR'"