Implement setgid script support.

TXR now notices that it's running setgid, and
implements setgid logic for scripts.

* sysif.c (orig_egid, real_gid, is_setgid): New static
variables.
(repress_privilege): Treat real and effective
group ID similarly to user ID. Save them in global
variables, and set the is_setgid flag.
(drop_privilege): Drop setgid privilege similarly
to setuid. Operate selectively: if neither setuid
nor setgid is in effect, do nothing, but if just
one is in effect, don't do anything for the other.
(simulate_setuid): Function renamed to simulate_setuid_setgid.
A small change is made here: if the fstat fails, just drop
privilege, don't abort. Implement setgid operation
independently of setuid. The is_setgid and is_setuid
flags are manipulated here now to get the drop_privileges
function to selectively drop setuid if we are running
a script which is only segid, or drop setgid if we are running
a setuid only script.

* sysif.h (simulate_setuid): Declaration name change to
simulate_setuid_setgid.

* txr.c (txr_main): Follow rename of simulate_setuid.

* txr.1: SETUID OPERATION section changed to SETUID/SETGID
operation, and setgid description worked into the text.

1 files changed, 2 insertions, 2 deletions

diff --git a/txr.c b/txr.c
index def35cc9..15d10168 100644
--- a/txr.c
+++ b/txr.c
@@ -789,7 +789,7 @@ int txr_main(int argc, char **argv)
   } else if (spec_file) {
     if (wcscmp(c_str(spec_file), L"-") != 0) {
       open_txr_file(spec_file, &txr_lisp_p, &spec_file_str, &parse_stream);
-      simulate_setuid(parse_stream);
+      simulate_setuid_setgid(parse_stream);
     } else {
       drop_privilege();
       spec_file_str = lit("stdin");
@@ -814,7 +814,7 @@ int txr_main(int argc, char **argv)
 
     if (!equal(arg, lit("-"))) {
       open_txr_file(arg, &txr_lisp_p, &spec_file_str, &parse_stream);
-      simulate_setuid(parse_stream);
+      simulate_setuid_setgid(parse_stream);
     } else {
       drop_privilege();
       spec_file_str = lit("stdin");