do_one_ref(): save and restore value of current_ref

If do_one_ref() is called recursively, then the inner call should not
permanently overwrite the value stored in current_ref by the outer
call.  Aside from the tiny optimization loss, peel_ref() expects the
value of current_ref not to change across a call to peel_entry().  But
in the presence of replace references that assumption could be
violated by a recursive call to do_one_ref:

do_for_each_entry()
do_one_ref()
builtin/describe.c:get_name()
peel_ref()
peel_entry()
peel_object ()
deref_tag_noverify()
parse_object()
lookup_replace_object()
do_lookup_replace_object()
prepare_replace_object()
do_for_each_ref()
do_for_each_entry()
do_for_each_entry_in_dir()
do_one_ref()

The inner call to do_one_ref() was unconditionally setting current_ref
to NULL when it was done, causing peel_ref() to perform an invalid
memory access.

So change do_one_ref() to save the old value of current_ref before
overwriting it, and restore the old value afterward rather than
setting it to NULL.

Reported-by: Mantas Mikulėnas <grawity@gmail.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/refs.c b/refs.c
index d17931a8bcd5322ab95f92094a009433f14d250a..f8ad1d608c6717e205a6c88064e971ffb6a9fcde 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -630,7 +630,9 @@ struct ref_entry_cb {
 static int do_one_ref(struct ref_entry *entry, void *cb_data)
 {
        struct ref_entry_cb *data = cb_data;
+       struct ref_entry *old_current_ref;
        int retval;
+
        if (prefixcmp(entry->name, data->base))
                return 0;
 
@@ -638,10 +640,12 @@ static int do_one_ref(struct ref_entry *entry, void *cb_data)
              !ref_resolves_to_object(entry))
                return 0;
 
+       /* Store the old value, in case this is a recursive call: */
+       old_current_ref = current_ref;
        current_ref = entry;
        retval = data->fn(entry->name + data->trim, entry->u.value.sha1,
                          entry->flag, data->cb_data);
-       current_ref = NULL;
+       current_ref = old_current_ref;
        return retval;
 }