From: Taylor Blau <me@ttaylorr.com>
To: Jeff King <peff@peff.net>
Cc: Derrick Stolee <derrickstolee@github.com>,
git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
Subject: Re: [PATCH 4/6] pack-bitmap.c: factor out manual `map_pos` manipulation
Date: Fri, 24 Mar 2023 19:23:06 -0400 [thread overview]
Message-ID: <ZB4w2gCo/qPCmWkz@nand.local> (raw)
In-Reply-To: <20230324182929.GA536252@coredump.intra.peff.net>
On Fri, Mar 24, 2023 at 02:29:29PM -0400, Jeff King wrote:
> We know the advance will succeed because we checked ahead of time that
> we had enough bytes. So it really is a BUG() if we don't, as it would
> indicate somebody missed the earlier check. On the other hand, it is a
> weird spot for an extra check, because by definition we'll have just
> read off the array just before the seek.
Here you claim that we want bitmap_index_seek_to() to call BUG() if we
end up with map_pos >= map_size. But...
> The case where we _do_ seek directly to a file-provided offset, rather
> than incrementing, is an important check that this series adds, but that
> one should be a die() and not a BUG().
...here you say that it should be a die().
I think it does depend on the context. When seeking directly to a
position before reading something, die()-ing is appropriate. The case
where you seek to a relative position to reflect that you just read
something, a BUG() is appropriate.
So really, I think you want something like this:
static void bitmap_index_seek_set(struct bitmap_index *bitmap_git, size_t pos)
{
if (pos >= bitmap_git->map_size)
die(_("bitmap position exceeds size (%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)bitmap_git->map_pos,
(uintmax_t)bitmap_git->map_size);
bitmap_git->map_pos = pos;
}
static void bitmap_index_seek_ahead(struct bitmap_index *bitmap_git,
size_t offset)
{
if (bitmap_git->map_pos + offset >= bitmap_git->map_size)
BUG("cannot seek %"PRIuMAX" byte(s) ahead of %"PRIuMAX" "
"(%"PRIuMAX" >= %"PRIuMAX")",
(uintmax_t)offset,
(uintmax_t)bitmap_git->map_pos,
(uintmax_t)(bitmap_git->map_pos + offset),
(uintmax_t)bitmap_git->map_size);
bitmap_git->map_pos += offset;
}
Does that match what you were thinking?
Thanks,
Taylor
next prev parent reply other threads:[~2023-03-24 23:23 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-20 20:02 [PATCH 0/6] pack-bitmap: miscellaneous mmap read hardening Taylor Blau
2023-03-20 20:02 ` [PATCH 1/6] pack-bitmap.c: hide bitmap internals in `read_u8()` Taylor Blau
2023-03-21 17:35 ` Jeff King
2023-03-24 17:52 ` Derrick Stolee
2023-03-20 20:02 ` [PATCH 2/6] pack-bitmap.c: hide bitmap internals in `read_be32()` Taylor Blau
2023-03-20 20:02 ` [PATCH 3/6] pack-bitmap.c: drop unnecessary 'inline's Taylor Blau
2023-03-21 17:40 ` Jeff King
2023-03-20 20:02 ` [PATCH 4/6] pack-bitmap.c: factor out manual `map_pos` manipulation Taylor Blau
2023-03-21 17:56 ` Jeff King
2023-03-24 18:04 ` Derrick Stolee
2023-03-24 18:29 ` Jeff King
2023-03-24 23:23 ` Taylor Blau [this message]
2023-03-25 4:57 ` Jeff King
2023-03-24 23:13 ` Taylor Blau
2023-03-24 23:24 ` Taylor Blau
2023-03-24 23:08 ` Taylor Blau
2023-03-20 20:02 ` [PATCH 5/6] pack-bitmap.c: use `bitmap_index_seek()` where possible Taylor Blau
2023-03-21 18:05 ` Jeff King
2023-03-24 18:06 ` Derrick Stolee
2023-03-24 18:35 ` Jeff King
2023-03-24 19:43 ` Junio C Hamano
2023-03-24 20:37 ` Jeff King
2023-03-24 21:38 ` Junio C Hamano
2023-03-24 22:57 ` Taylor Blau
2023-03-20 20:02 ` [PATCH 6/6] pack-bitmap.c: factor out `bitmap_index_seek_commit()` Taylor Blau
2023-03-21 18:13 ` Jeff King
2023-03-21 18:16 ` Taylor Blau
2023-03-21 18:27 ` Jeff King
2023-03-24 18:09 ` Derrick Stolee
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