From: Phillip Wood <phillip.wood123@gmail.com>
To: Jeff King <peff@peff.net>, Junio C Hamano <gitster@pobox.com>
Cc: "Thomas Bock" <bockthom@cs.uni-saarland.de>,
"Derrick Stolee" <derrickstolee@github.com>,
git@vger.kernel.org, "René Scharfe" <l.s.r@web.de>
Subject: Re: [PATCH v3 3/4] parse_commit(): handle broken whitespace-only timestamp
Date: Thu, 27 Apr 2023 11:11:12 +0100 [thread overview]
Message-ID: <a04e7950-b74e-d43f-4d19-86def079748c@gmail.com> (raw)
In-Reply-To: <20230427081715.GA1478467@coredump.intra.peff.net>
On 27/04/2023 09:17, Jeff King wrote:
> The comment in parse_commit_date() claims that parse_timestamp() will
> not walk past the end of the buffer we've been given, since it will hit
> the newline at "eol" and stop. This is usually true, when dateptr
> contains actual numbers to parse. But with a line like:
>
> committer name <email> \n
>
> with just whitespace, and no numbers, parse_timestamp() will consume
> that newline as part of the leading whitespace, and we may walk past our
> "tail" pointer (which itself is set from the "size" parameter passed in
> to parse_commit_buffer()).
>
> In practice this can't cause us to walk off the end of an array, because
> we always add an extra NUL byte to the end of objects we load from disk
> (as a defense against exactly this kind of bug). However, you can see
> the behavior in action when "committer" is the final header (which it
> usually is, unless there's an encoding) and the subject line can be
> parsed as an integer. We walk right past the newline on the committer
> line, as well as the "\n\n" separator, and mistake the subject for the
> timestamp.
>
> We can solve this by trimming the whitespace ourselves, making sure that
> it has some non-whitespace to parse. Note that we need to be a bit
> careful about the definition of "whitespace" here, as our isspace()
> doesn't match exotic characters like vertical tab or formfeed. We can
> work around that by checking for an actual number (see the in-code
> comment). This is slightly more restrictive than the current code, but
> in practice the results are either the same (we reject "foo" as "0", but
> so would parse_timestamp()) or extremely unlikely even for broken
> commits (parse_timestamp() would allow "\v123" as "123", but we'll now
> make it "0").
>
> I did also allow "-" here, which may be controversial, as we don't
> currently support negative timestamps. My reasoning was two-fold. One,
> the design of parse_timestamp() is such that we should be able to easily
> switch it to handling signed values, and this otherwise creates a
> hard-to-find gotcha that anybody doing that work would get tripped up
> on. And two, the status quo is that we currently parse them, though the
> result of course ends up as a very large unsigned value (which is likely
> to just get clamped to "0" for display anyway, since our date routines
> can't handle it).
I think this makes a good case for accepting '-'. The commit message is
well explained as always :-) This all looks good to me apart from a
query about one of the tests.
> The new test checks the commit parser (via "--until") for both vanilla
> spaces and the vertical-tab case. I also added a test to check these
> against the pretty-print formatter, which uses split_ident_line(). It's
> not subject to the same bug, because it already insists that there be
> one or more digits in the timestamp.
>
> Helped-by: Phillip Wood <phillip.wood123@gmail.com>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> commit.c | 28 ++++++++++++++++++++++++++--
> t/t4212-log-corrupt.sh | 41 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 67 insertions(+), 2 deletions(-)
>
> +test_expect_success 'create commits with whitespace committer dates' '
> + # It is important that this subject line is numeric, since we want to
> + # be sure we are not confused by skipping whitespace and accidentally
> + # parsing the subject as a timestamp.
> + #
> + # Do not use munge_author_date here. Besides not hitting the committer
> + # line, it leaves the timezone intact, and we want nothing but
> + # whitespace.
> + #
> + # We will make two munged commits here. The first, ws_commit, will
> + # be purely spaces. The second contains a vertical tab, which is
> + # considered a space by strtoumax(), but not by our isspace().
This comment is really helpful to explain what's going on and testing
'\v' as well as ' ' is a good idea.
> + test_commit 1234567890 &&
> + git cat-file commit HEAD >commit.orig &&
> + sed "s/>.*/> /" <commit.orig >commit.munge &&
> + ws_commit=$(git hash-object --literally -w -t commit commit.munge) &&
> + sed "s/>.*/> $(printf "\013")/" <commit.orig >commit.munge &&
Does the shell eat the '\v' when it trims trailing whitespace from the
command substitution (I can't remember the rules off the top of my head)?
Best Wishes
Phillip
> + vt_commit=$(git hash-object --literally -w -t commit commit.munge)
> +'
> +
> +test_expect_success '--until treats whitespace date as sentinel' '
> + echo $ws_commit >expect &&
> + git rev-list --until=1980-01-01 $ws_commit >actual &&
> + test_cmp expect actual &&
> +
> + echo $vt_commit >expect &&
> + git rev-list --until=1980-01-01 $vt_commit >actual &&
> + test_cmp expect actual
> +'
> +
> +test_expect_success 'pretty-printer handles whitespace date' '
> + # as with the %ad test above, we will show these as the empty string,
> + # not the 1970 epoch date. This is intentional; see 7d9a281941 (t4212:
> + # test bogus timestamps with git-log, 2014-02-24) for more discussion.
> + echo : >expect &&
> + git log -1 --format="%at:%ct" $ws_commit >actual &&
> + test_cmp expect actual &&
> + git log -1 --format="%at:%ct" $vt_commit >actual &&
> + test_cmp expect actual
> +'
> +
> test_done
next prev parent reply other threads:[~2023-04-27 10:11 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-14 11:37 Weird behavior of 'git log --before' or 'git log --date-order': Commits from 2011 are treated to be before 1980 Thomas Bock
2023-04-15 8:52 ` Jeff King
2023-04-15 8:59 ` Jeff King
2023-04-15 14:10 ` Kristoffer Haugsbakk
2023-04-17 5:40 ` Jeff King
2023-04-17 6:20 ` Kristoffer Haugsbakk
2023-04-17 7:41 ` Jeff King
2023-04-27 22:32 ` Kristoffer Haugsbakk
2023-04-17 9:51 ` Junio C Hamano
2023-04-18 4:12 ` Jeff King
2023-04-18 14:02 ` Derrick Stolee
2023-04-21 14:51 ` Thomas Bock
2023-04-22 13:41 ` [PATCH 0/3] fixing some parse_commit() timestamp corner cases Jeff King
2023-04-22 13:42 ` [PATCH 1/3] t4212: avoid putting git on left-hand side of pipe Jeff King
2023-04-22 13:47 ` [PATCH 2/3] parse_commit(): parse timestamp from end of line Jeff King
2023-04-24 17:05 ` Junio C Hamano
2023-04-25 5:23 ` Jeff King
2023-04-24 16:39 ` [PATCH 0/3] fixing some parse_commit() timestamp corner cases Junio C Hamano
2023-04-25 5:52 ` [PATCH v2 " Jeff King
2023-04-25 5:54 ` Jeff King
2023-04-25 5:54 ` [PATCH v2 1/4] t4212: avoid putting git on left-hand side of pipe Jeff King
2023-04-25 5:54 ` [PATCH v2 2/4] parse_commit(): parse timestamp from end of line Jeff King
2023-04-25 5:54 ` [PATCH v2 3/4] parse_commit(): handle broken whitespace-only timestamp Jeff King
2023-04-25 10:11 ` Phillip Wood
2023-04-25 16:06 ` Junio C Hamano
2023-04-26 11:36 ` Jeff King
2023-04-26 15:32 ` Junio C Hamano
2023-04-27 8:13 ` [PATCH v3 0/4] fixing some parse_commit() timestamp corner cases Jeff King
2023-04-27 8:14 ` [PATCH v3 1/4] t4212: avoid putting git on left-hand side of pipe Jeff King
2023-04-27 8:14 ` [PATCH v3 2/4] parse_commit(): parse timestamp from end of line Jeff King
2023-04-27 8:17 ` [PATCH v3 3/4] parse_commit(): handle broken whitespace-only timestamp Jeff King
2023-04-27 10:11 ` Phillip Wood [this message]
2023-04-27 11:55 ` Phillip Wood
2023-04-27 16:46 ` Jeff King
2023-04-27 16:20 ` Junio C Hamano
2023-04-27 16:55 ` Jeff King
2023-04-27 16:25 ` Junio C Hamano
2023-04-27 16:57 ` Jeff King
2023-04-27 8:17 ` [PATCH v3 4/4] parse_commit(): describe more date-parsing failure modes Jeff King
2023-04-27 8:18 ` [PATCH v3 0/4] fixing some parse_commit() timestamp corner cases Jeff King
2023-04-27 16:32 ` Junio C Hamano
2023-04-26 14:06 ` [PATCH v2 3/4] parse_commit(): handle broken whitespace-only timestamp Phillip Wood
2023-04-26 14:31 ` Andreas Schwab
2023-04-26 14:44 ` Phillip Wood
2023-04-25 5:55 ` [PATCH v2 4/4] parse_commit(): describe more date-parsing failure modes Jeff King
2023-04-22 13:52 ` Weird behavior of 'git log --before' or 'git log --date-order': Commits from 2011 are treated to be before 1980 Jeff King
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