Remove gete?[ug]id caching

Currently we cache the UID/GID and effective UID/GID similarly to how
we used to cache getpid() before v5.14.0-251-g0e21945. Remove this
magical behavior in favor of always calling getpid(), getgid()
etc. This resolves RT #96208.

A minimal testcase for this is the following by Leon Timmermans
attached to RT #96208:

    eval { require 'syscall.ph'; 1 } or eval { require 'sys/syscall.ph'; 1 } or die $@;

    if (syscall(&SYS_setuid, $ARGV[0] + 0 || 1000) >= 0 or die "$!") {
            printf "\$< = %d, getuid = %d\n", $<, syscall(&SYS_getuid);
    }

I.e. if we call the sete?[ug]id() functions unbeknownst to perl the
$<, $>, $( and $) variables won't be updated. This results in the same
sort of issues we had with $$ before v5.14.0-251-g0e21945, and
getppid() before my v5.15.7-407-gd7c042c patch.

I'm completely eliminating the PL_egid, PL_euid, PL_gid and PL_uid
variables as part of this patch, this will break some CPAN modules,
but it'll be really easy before the v5.16.0 final to reinstate
them. I'd like to remove them to see what breaks, and how easy it is
to fix it.

These variables are not part of the public API, and the modules using
them could either use the Perl_gete?[ug]id() functions or are working
around the bug I'm fixing with this commit.

The new PL_delaymagic_(egid|euid|gid|uid) variables I'm adding are
*only* intended to be used internally in the interpreter to facilitate
the delaymagic in Perl_pp_sassign. There's probably some way not to
export these to programs that embed perl, but I haven't found out how
to do that.

1 files changed, 19 insertions, 16 deletions

diff --git a/perl.c b/perl.c
index c384e6d18e..b238d04ef0 100644
--- a/perl.c
+++ b/perl.c
@@ -3754,13 +3754,18 @@ S_validate_suid(pTHX_ PerlIO *rsfp)
 {
     PERL_ARGS_ASSERT_VALIDATE_SUID;
 
-    if (PL_euid != PL_uid || PL_egid != PL_gid) {	/* (suidperl doesn't exist, in fact) */
+    const UV  my_uid = PerlProc_getuid();
+    const UV my_euid = PerlProc_geteuid();
+    const UV  my_gid = PerlProc_getgid();
+    const UV my_egid = PerlProc_getegid();
+
+    if (my_euid != my_uid || my_egid != my_gid) {	/* (suidperl doesn't exist, in fact) */
 	dVAR;
 
 	PerlLIO_fstat(PerlIO_fileno(rsfp),&PL_statbuf);	/* may be either wrapped or real suid */
-	if ((PL_euid != PL_uid && PL_euid == PL_statbuf.st_uid && PL_statbuf.st_mode & S_ISUID)
+	if ((my_euid != my_uid && my_euid == PL_statbuf.st_uid && PL_statbuf.st_mode & S_ISUID)
 	    ||
-	    (PL_egid != PL_gid && PL_egid == PL_statbuf.st_gid && PL_statbuf.st_mode & S_ISGID)
+	    (my_egid != my_gid && my_egid == PL_statbuf.st_gid && PL_statbuf.st_mode & S_ISGID)
 	   )
 	    if (!PL_do_undump)
 		Perl_croak(aTHX_ "YOU HAVEN'T DISABLED SET-ID SCRIPTS IN THE KERNEL YET!\n\
@@ -3804,17 +3809,14 @@ STATIC void
 S_init_ids(pTHX)
 {
     dVAR;
-    PL_uid = PerlProc_getuid();
-    PL_euid = PerlProc_geteuid();
-    PL_gid = PerlProc_getgid();
-    PL_egid = PerlProc_getegid();
-#ifdef VMS
-    PL_uid |= PL_gid << 16;
-    PL_euid |= PL_egid << 16;
-#endif
+    const UV my_uid = PerlProc_getuid();
+    const UV my_euid = PerlProc_geteuid();
+    const UV my_gid = PerlProc_getgid();
+    const UV my_egid = PerlProc_getegid();
+
     /* Should not happen: */
-    CHECK_MALLOC_TAINT(PL_uid && (PL_euid != PL_uid || PL_egid != PL_gid));
-    PL_tainting |= (PL_uid && (PL_euid != PL_uid || PL_egid != PL_gid));
+    CHECK_MALLOC_TAINT(my_uid && (my_euid != my_uid || my_egid != my_gid));
+    PL_tainting |= (my_uid && (my_euid != my_uid || my_egid != my_gid));
     /* BUG */
     /* PSz 27 Feb 04
      * Should go by suidscript, not uid!=euid: why disallow
@@ -3880,9 +3882,9 @@ S_forbid_setid(pTHX_ const char flag, const bool suidscript) /* g */
     }
 
 #ifdef SETUID_SCRIPTS_ARE_SECURE_NOW
-    if (PL_euid != PL_uid)
+    if (PerlProc_getuid() != PerlProc_geteuid())
         Perl_croak(aTHX_ "No %s allowed while running setuid", message);
-    if (PL_egid != PL_gid)
+    if (PerlProc_getgid() != PerlProc_getegid())
         Perl_croak(aTHX_ "No %s allowed while running setgid", message);
 #endif /* SETUID_SCRIPTS_ARE_SECURE_NOW */
     if (suidscript)
@@ -4566,7 +4568,8 @@ S_mayberelocate(pTHX_ const char *const dir, STRLEN len, U32 flags)
 		    /* And this is the new libdir.  */
 		    libdir = tempsv;
 		    if (PL_tainting &&
-			(PL_uid != PL_euid || PL_gid != PL_egid)) {
+			(PerlProc_getuid() != PerlProc_geteuid() ||
+			 PerlProc_getgid() != PerlProc_getegid())) {
 			/* Need to taint relocated paths if running set ID  */
 			SvTAINTED_on(libdir);
 		    }