Forbid ++ and -- on readonly values

Subject: You can ++ and -- readonly integer scalars? (patch included)

  I managed to find an illustration of the bug in a perl one-liner:

perl -e '*a = \100; $a++; print "$a\n"'
101

  Perhaps that's been fixed in one of the beta releases which I'm not
running; or perhaps I'm the only one who finds that slightly incorrect.
If so, ignore the rest of this message.

  You can modify readonly scalars using any of the pre/post
increment/decrement operators. Apparently, the only readonly checking is
done for cases like '100++'.

  I managed to find the relevant code and add some SvREADONLY checks. It
now dies on the inc/dec of readonly scalars with the appropriate nasty
message. I just thought I'd share my patch.

Ashley Winters

p5p-msgid: <Pine.LNX.3.95.970110193330.11249D-100000@jql.accessone.com>

2 files changed, 8 insertions, 0 deletions

diff --git a/pp.c b/pp.c
index 48e332198b..f4cdc2dd63 100644
--- a/pp.c
+++ b/pp.c
@@ -575,6 +575,8 @@ PP(pp_undef)
 PP(pp_predec)
 {
     dSP;
+    if (SvREADONLY(TOPs))
+       croak(no_modify);
     if (SvIOK(TOPs)) {
     	if (SvIVX(TOPs) == IV_MIN) {
     	    sv_setnv(TOPs, (double)SvIVX(TOPs) - 1.0);
@@ -593,6 +595,8 @@ PP(pp_predec)
 PP(pp_postinc)
 {
     dSP; dTARGET;
+    if (SvREADONLY(TOPs))
+       croak(no_modify);
     sv_setsv(TARG, TOPs);
     if (SvIOK(TOPs)) {
     	if (SvIVX(TOPs) == IV_MAX) {
@@ -615,6 +619,8 @@ PP(pp_postinc)
 PP(pp_postdec)
 {
     dSP; dTARGET;
+    if(SvREADONLY(TOPs))
+       croak(no_modify);
     sv_setsv(TARG, TOPs);
     if (SvIOK(TOPs)) {
     	if (SvIVX(TOPs) == IV_MIN) {
diff --git a/pp_hot.c b/pp_hot.c
index 150afe27f0..f1ee8f2c84 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -251,6 +251,8 @@ PP(pp_eq)
 PP(pp_preinc)
 {
     dSP;
+    if (SvREADONLY(TOPs))
+       croak(no_modify);
     if (SvIOK(TOPs)) {
     	if (SvIVX(TOPs) == IV_MAX) {
     	    sv_setnv(TOPs, (double)(SvIVX(TOPs)) + 1.0 );