From: Jeff King <peff@peff.net>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Jonathan Tan <jonathantanmy@google.com>
Subject: Re: [PATCH 5/5] packfile: inline custom read_object()
Date: Thu, 12 Jan 2023 11:29:03 -0500 [thread overview]
Message-ID: <Y8A1T5kzgqXV5vKr@coredump.intra.peff.net> (raw)
In-Reply-To: <230112.86o7r42k13.gmgdl@evledraar.gmail.com>
On Thu, Jan 12, 2023 at 10:01:28AM +0100, Ævar Arnfjörð Bjarmason wrote:
> > - base = read_object(r, &base_oid, &type, &base_size);
> > +
> > + oi.typep = &type;
> > + oi.sizep = &base_size;
> > + oi.contentp = &base;
> > + if (oid_object_info_extended(r, &base_oid, &oi, 0) < 0)
> > + base = NULL;
> > +
> > external_base = base;
> > }
> > }
>
> This isn't introducing a behavior difference, in fact it's diligently
> bending over backwards to preserve existing behavior, but I don't think
> we need to do so, and shouldn't have this "base = NULL" line.
>
> Here we're within an "if" block where we tested that "base == NULL"
> (which is why we're trying to populate it)
>
> Before when we had read_object() re-assigning to "base" here was the
> obvious thing to do, but now this seems like undue an incomplete
> paranoia.
I think it's the same paranoia that was in read_object(). There it
catches the error and returns NULL, rather than the probably-NULL
"content" (though to be fair, it simply did not initialize the pointer,
so it would have had to do that to depend on it).
I agree it's probably being overly defensive. But I don't think
oid_object_info_extended() makes any promises, and it's not completely
clear to me if packed_object_info() could return a non-NULL entry here
on an error (e.g., if packed_to_object_type() fails even after we pulled
out the content).
So probably yes, we could depend on that (and if not, arguably we should
be fixing oid_object_info_extended(), because we are probably leaking a
buffer in that case). But we definitely shouldn't be doing it in the
middle of another patch.
> If oid_object_info_extended() why can't we trust that it didn't touch
> our "base"? And if we can't trust that, why are we trusting that it left
> "type" and "base_size" untouched?
My assumption is that "base" gated access to "type" and "base_size". So
as long as "!base", we do not look at the other two.
> I think squashing this in would be much better:
>
> diff --git a/packfile.c b/packfile.c
> index 79e21ab18e7..f45017422a1 100644
> --- a/packfile.c
> +++ b/packfile.c
> @@ -1795,10 +1795,8 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
> oi.typep = &type;
> oi.sizep = &base_size;
> oi.contentp = &base;
> - if (oid_object_info_extended(r, &base_oid, &oi, 0) < 0)
> - base = NULL;
> -
> - external_base = base;
> + if (!oid_object_info_extended(r, &base_oid, &oi, 0))
> + external_base = base;
> }
> }
>
> Not only aren't we second-guessing that our "base" was left alone, we're
> using the return value of oid_object_info_extended() to guard that
> assignment to "external_base" instead (it's NULL at this point too).
I don't think we need to guard the assignment (we know it will be NULL
if we saw an error). But sure, I don't mind if you want to do that
simplification, but it should be on top if at all.
-Peff
next prev parent reply other threads:[~2023-01-12 16:31 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-07 13:48 [PATCH 0/5] cleaning up read_object() family of functions Jeff King
2023-01-07 13:48 ` [PATCH 1/5] object-file: inline calls to read_object() Jeff King
2023-01-12 9:13 ` Ævar Arnfjörð Bjarmason
2023-01-12 16:06 ` [PATCH] object-file: fix indent-with-space Jeff King
2023-01-12 16:08 ` Ævar Arnfjörð Bjarmason
2023-01-13 17:40 ` Junio C Hamano
2023-01-07 13:49 ` [PATCH 2/5] streaming: inline call to read_object_file_extended() Jeff King
2023-01-07 13:50 ` [PATCH 3/5] read_object_file_extended(): drop lookup_replace option Jeff King
2023-01-07 13:50 ` [PATCH 4/5] repo_read_object_file(): stop wrapping read_object_file_extended() Jeff King
2023-01-07 13:50 ` [PATCH 5/5] packfile: inline custom read_object() Jeff King
2023-01-12 9:01 ` Ævar Arnfjörð Bjarmason
2023-01-12 16:29 ` Jeff King [this message]
2023-01-09 15:09 ` [PATCH 0/5] cleaning up read_object() family of functions Derrick Stolee
2023-01-11 18:26 ` Jeff King
2023-01-11 20:17 ` Derrick Stolee
2023-01-11 20:30 ` Jeff King
2023-01-12 9:21 ` Ævar Arnfjörð Bjarmason
2023-01-12 16:16 ` Jeff King
2023-01-12 16:22 ` Ævar Arnfjörð Bjarmason
2023-01-12 16:53 ` Jeff King
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