Re: New NULL dereference in sequence.c

> Hi all,
>
> The last defect Sentry picked up has been removed, yay!  At the same
> time, a new NULL dereference bug appeared, in sequencer.c:
>
>      static int is_index_unchanged(void)
>      {
>          unsigned char head_sha1[20];
>          struct commit *head_commit;
>
>          if (!resolve_ref_unsafe("HEAD", head_sha1, 1, NULL))
>              return error(_("Could not resolve HEAD commit\n"));
>
>          head_commit = lookup_commit(head_sha1);
>          if (!head_commit || parse_commit(head_commit))
>              return error(_("could not parse commit %s\n"),
>                       sha1_to_hex(head_commit->object.sha1));
>
> In the last line quoted above, head_commit may be NULL, and it is
> dereferenced in the call to sha1_to_hex.  Assuming lookup_commit(head_sha1)
> can return NULL, this function will segfault.
>
> Introduced here:
> https://github.com/gitster/git/commit/b27cfb0#sequencer.c