On Mon, Oct 04 2021, Phillip Wood wrote: > Hi Ævar > > On 04/10/2021 01:46, Ævar Arnfjörð Bjarmason wrote: >> Change the clear_unpack_trees_porcelain() to be like a *_release() >> function, not a *_reset() (in strbuf.c terms). Let's move the only API >> user that relied on the latter to doing its own >> unpack_trees_options_init(). See the commit that introduced >> unpack_trees_options_init() for details on the control flow involved >> here. > > Before this change if there was a call to unpack_trees() after > clear_unpack_trees_porcelain() then that caller would get the default > error messages. After this change we end up with a use-after-free > error in that situation. I found the subject line of this patch hard > to understand, the commit message explains what it is doing but I'm > still not sure what the motivation for this change is. I'll work on the commit message part. With this series such a caller is purely hypothetical, isn't it? I.e. the journey in 02/10 & 04/10, and later in the 07/10 you commented on is to make the API behave similarly to e.g. strbuf, where there's a release() that leaves it in such a state, different from a "reset". Perhaps this step in isolation is confusing at it leaves the function named as clear_unpack_trees_porcelain(). I had this all in one change initially, but figured having such a large rename diff & one behavior change was worse. We could just leave the "reset" semantics in place for everyone, but just like "strbuf_release()" et al I think it's good for self-documentation purposes to explicitly make clear if you're re-using the struct, or just freeing it at the end. For this API only one user of the API cares about the re-use case, merge-recursive.c. >> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> >> --- >> merge-recursive.c | 1 + >> unpack-trees.c | 1 - >> 2 files changed, 1 insertion(+), 1 deletion(-) >> diff --git a/merge-recursive.c b/merge-recursive.c >> index d24a4903f1d..a77f66b006c 100644 >> --- a/merge-recursive.c >> +++ b/merge-recursive.c >> @@ -442,6 +442,7 @@ static void unpack_trees_finish(struct merge_options *opt) >> { >> discard_index(&opt->priv->orig_index); >> clear_unpack_trees_porcelain(&opt->priv->unpack_opts); >> + unpack_trees_options_init(&opt->priv->unpack_opts); >> } >> static int save_files_dirs(const struct object_id *oid, >> diff --git a/unpack-trees.c b/unpack-trees.c >> index 94767d3f96f..e7365322e82 100644 >> --- a/unpack-trees.c >> +++ b/unpack-trees.c >> @@ -197,7 +197,6 @@ void clear_unpack_trees_porcelain(struct unpack_trees_options *opts) >> { >> strvec_clear(&opts->msgs_to_free); >> dir_clear(&opts->dir); >> - memset(opts->msgs, 0, sizeof(opts->msgs)); >> } >> static int do_add_entry(struct unpack_trees_options *o, struct >> cache_entry *ce, >>