pp_ctl.c - copy hook into %INC not alias it

When an @INC hook is executed and it updates %INC it can result in @INC
being updated and the hook being destroyed.

This seems to be because the SV fetched from @INC is stored into %INC
directly, essentially creating an alias (in perl terms) of the original.
When the alias is updated, for instance by setting it to be a string,
this is reflected in both @INC and %INC.

By copying the sv before we store it we avoid this problem.

We can't run the test under miniperl as it uses IO layers.

This should fix GH #20577.

1 files changed, 4 insertions, 1 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index 1e6dda7e98..fb760ee183 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -4605,10 +4605,13 @@ S_require_file(pTHX_ SV *sv)
         (void)hv_store(GvHVn(PL_incgv),
                        unixname, unixlen, newSVpv(tryname,0),0);
     } else {
+        /* store the hook in the sv, note we have to *copy* hook_sv,
+         * we don't want modifications to it to change @INC - see GH #20577
+         */
         SV** const svp = hv_fetch(GvHVn(PL_incgv), unixname, unixlen, 0);
         if (!svp)
             (void)hv_store(GvHVn(PL_incgv),
-                           unixname, unixlen, SvREFCNT_inc_simple(hook_sv), 0 );
+                           unixname, unixlen, newSVsv(hook_sv), 0 );
     }
 
     /* Now parse the file */