Fix processing of PERL_ENV_TABLES.

In a35dcc95dd24524931e I "improved" string safety in vms/vms.c by
converting to my_strlcpy and my_strlcat, but mangled the length
argument to my_strlcat when adding the name of the logical name
table specified in PERL_ENV_TABLES. This caused the command string
to be truncated, so a command that, for example, should have been:

    $ Show Logical * /Table=LNM$JOB
    ...

actually became:

    $ Show Logical * /Table=
    %DCL-W-VALREQ, missing qualifier or keyword value - supply all required values

Plus it turns out the strings holding the names of the tables were
being stored in dynamic string descriptors and were not
NUL-terminated, but the strl* functions require NUL-terminated
arguments.  So change those to static string descriptors and
allocate the exact amount of storage needed including room for a
NUL.

This was a regression in 5.16.0, first reported a couple of days
ago by Mark Daniel on comp.os.vms:

Date: Fri, 06 Sep 2013 12:56:01 +0930
From: Mark Daniel <mark.daniel [AT] wasd.vsm.com.au>
Newsgroups: comp.os.vms
Message-ID: <52294b4a$0$2875$c3e8da3$76491128@news.astraweb.com>

TODO: Figure out how and where to test this.

1 files changed, 6 insertions, 5 deletions

diff --git a/vms/vms.c b/vms/vms.c
index 1c93728af0..7ccda3180f 100644
--- a/vms/vms.c
+++ b/vms/vms.c
@@ -1371,7 +1371,7 @@ prime_env_iter(void)
       my_strlcpy(cmd, "Show Logical *", sizeof(cmd));
       if (str$case_blind_compare(env_tables[i],&fildevdsc)) {
         my_strlcat(cmd," /Table=", sizeof(cmd));
-        cmddsc.dsc$w_length = my_strlcat(cmd, env_tables[i]->dsc$a_pointer, env_tables[i]->dsc$w_length + 1);
+        cmddsc.dsc$w_length = my_strlcat(cmd, env_tables[i]->dsc$a_pointer, sizeof(cmd));
       }
       else cmddsc.dsc$w_length = 14;  /* N.B. We test this below */
       flags = defflags | CLI$M_NOCLISYM;
@@ -9658,11 +9658,12 @@ vms_image_init(int *argcp, char ***argvp)
     }
     tabvec[tabidx] = (struct dsc$descriptor_s *) PerlMem_malloc(sizeof(struct dsc$descriptor_s));
     if (tabvec[tabidx] == NULL) _ckvmssts_noperl(SS$_INSFMEM);
-    tabvec[tabidx]->dsc$w_length  = 0;
+    tabvec[tabidx]->dsc$w_length  = len;
     tabvec[tabidx]->dsc$b_dtype   = DSC$K_DTYPE_T;
-    tabvec[tabidx]->dsc$b_class   = DSC$K_CLASS_D;
-    tabvec[tabidx]->dsc$a_pointer = NULL;
-    _ckvmssts_noperl(lib$scopy_r_dx(&len,eqv,tabvec[tabidx]));
+    tabvec[tabidx]->dsc$b_class   = DSC$K_CLASS_S;
+    tabvec[tabidx]->dsc$a_pointer = PerlMem_malloc(len + 1);
+    if (tabvec[tabidx]->dsc$a_pointer == NULL) _ckvmssts_noperl(SS$_INSFMEM);
+    my_strlcpy(tabvec[tabidx]->dsc$a_pointer, eqv, len + 1);
   }
   if (tabidx) { tabvec[tabidx] = NULL; env_tables = tabvec; }