ash: eval: avoid leaking memory associated with redirections. Closes 7748

The following constructs result in ever-increasing memory usage:

   while true; do { true; } </dev/null; done
   while true; do ( true; ) </dev/null; done

For comparison, bash displays static memory usage in both cases.

This has been fixed in dash by commit 2bc6caa.  The maintainer
writes:

   I have simplified evaltree so that it simply sets the stack mark
   unconditionally.  This allows us to remove the stack marks in the
   functions called by evaltree.

Closes BusyBox bug 7748.

function                                             old     new   delta
evaltree                                             606     632     +26
evalcommand                                         1724    1696     -28
evalcase                                             382     351     -31
evalfor                                              230     196     -34
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/3 up/down: 26/-93)            Total: -67 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 4 insertions, 10 deletions

diff --git a/shell/ash.c b/shell/ash.c
index a284b084d..a4394d756 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -9034,8 +9034,11 @@ evaltree(union node *n, int flags)
 {
         int checkexit = 0;
         int (*evalfn)(union node *, int);
+        struct stackmark smark;
         int status = 0;
 
+        setstackmark(&smark);
+
         if (n == NULL) {
                 TRACE(("evaltree(NULL) called\n"));
                 goto out;
@@ -9149,6 +9152,7 @@ evaltree(union node *n, int flags)
         if (flags & EV_EXIT)
                 raise_exception(EXEXIT);
 
+        popstackmark(&smark);
         TRACE(("leaving evaltree (no interrupts)\n"));
         return exitstatus;
 }
@@ -9209,14 +9213,12 @@ evalfor(union node *n, int flags)
         struct arglist arglist;
         union node *argp;
         struct strlist *sp;
-        struct stackmark smark;
         int status = 0;
 
         errlinno = lineno = n->ncase.linno;
         if (funcline)
                 lineno -= funcline - 1;
 
-        setstackmark(&smark);
         arglist.list = NULL;
         arglist.lastp = &arglist.list;
         for (argp = n->nfor.args; argp; argp = argp->narg.next) {
@@ -9233,7 +9235,6 @@ evalfor(union node *n, int flags)
                         break;
         }
         loopnest--;
-        popstackmark(&smark);
 
         return status;
 }
@@ -9244,14 +9245,12 @@ evalcase(union node *n, int flags)
         union node *cp;
         union node *patp;
         struct arglist arglist;
-        struct stackmark smark;
         int status = 0;
 
         errlinno = lineno = n->ncase.linno;
         if (funcline)
                 lineno -= funcline - 1;
 
-        setstackmark(&smark);
         arglist.list = NULL;
         arglist.lastp = &arglist.list;
         expandarg(n->ncase.expr, &arglist, EXP_TILDE);
@@ -9270,8 +9269,6 @@ evalcase(union node *n, int flags)
                 }
         }
  out:
-        popstackmark(&smark);
-
         return status;
 }
 
@@ -9970,7 +9967,6 @@ evalcommand(union node *cmd, int flags)
         struct localvar_list *localvar_stop;
         struct parsefile *file_stop;
         struct redirtab *redir_stop;
-        struct stackmark smark;
         union node *argp;
         struct arglist arglist;
         struct arglist varlist;
@@ -9992,7 +9988,6 @@ evalcommand(union node *cmd, int flags)
 
         /* First expand the arguments. */
         TRACE(("evalcommand(0x%lx, %d) called\n", (long)cmd, flags));
-        setstackmark(&smark);
         localvar_stop = pushlocalvars();
         file_stop = g_parsefile;
         back_exitstatus = 0;
@@ -10275,7 +10270,6 @@ evalcommand(union node *cmd, int flags)
                  */
                 setvar0("_", lastarg);
         }
-        popstackmark(&smark);
 
         return status;
 }