[PATCH v2] [GSOC] ref-filter: fix read invalid union member bug

From: ZheNing Hu <adlternative@gmail.com>

used_atom.u is an union, and it has different members depending on what atom the auxiliary data the union part of the "struct used_atom" wants to record. At most only one of the members can be valid at any one time. Since the code checks u.remote_ref without even making sure if the atom is "push" or "push:" (which are only two cases that u.remote_ref.push becomes valid), but u.remote_ref shares the same storage for other members of the union, the check was reading from an invalid member, which was the bug.

Modify the condition here to first check whether the atom name starts with "push", and then check u.remote_ref, to avoid reading the value of invalid member of the union.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: ZheNing Hu <adlternative@gmail.com>
---
    [GSOC] ref-filter: fix read invalid union member bug
    
    Change from last version: Modified the documentation description with
    the help of Junio. And modify the processing method of the condition:
    check whether the name of the atom starts with "push" and whether
    u.remote_ref is non-zero.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-949%2Fadlternative%2Fref-filter-enum-bug-fix-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-949/adlternative/ref-filter-enum-bug-fix-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/949

Range-diff vs v1:

 1:  e51ca176f76b ! 1:  0e1923c9d722 [GSOC] ref-filter: solve bugs caused by enumeration
     @@ Metadata
      Author: ZheNing Hu <adlternative@gmail.com>
      
       ## Commit message ##
     -    [GSOC] ref-filter: solve bugs caused by enumeration
     +    [GSOC] ref-filter: fix read invalid union member bug
      
     -    Johannes Schindelin seems to have introduced a bug in
     -    cc72385f(for-each-ref: let upstream/push optionally
     -    report the remote name), it use `atom->u.remote_ref.option`
     -    which is a member of enumeration in the judgment statement.
     -    When we use other members in the enumeration `used_atom.u`,
     -    and it happened to fill in `remote_ref.push`, this judgment
     -    may still be established and produces errors. So replace the
     -    judgment statement with `starts_with(name, "push")` to fix
     -    the error.
     +    used_atom.u is an union, and it has different members depending on
     +    what atom the auxiliary data the union part of the "struct
     +    used_atom" wants to record.  At most only one of the members can be
     +    valid at any one time.  Since the code checks u.remote_ref without
     +    even making sure if the atom is "push" or "push:" (which are only
     +    two cases that u.remote_ref.push becomes valid), but u.remote_ref
     +    shares the same storage for other members of the union, the check
     +    was reading from an invalid member, which was the bug.
      
     +    Modify the condition here to first check whether the atom name
     +    starts with "push", and then check u.remote_ref, to avoid reading
     +    the value of invalid member of the union.
     +
     +    Helped-by: Junio C Hamano <gitster@pobox.com>
          Signed-off-by: ZheNing Hu <adlternative@gmail.com>
      
       ## ref-filter.c ##
     @@ ref-filter.c: static int populate_value(struct ref_array_item *ref, struct strbu
       				v->s = xstrdup("");
       			continue;
      -		} else if (atom->u.remote_ref.push) {
     -+		} else if (starts_with(name, "push")) {
     ++		} else if (starts_with(name, "push") && atom->u.remote_ref.push) {
       			const char *branch_name;
       			v->s = xstrdup("");
       			if (!skip_prefix(ref->refname, "refs/heads/",

 ref-filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)