From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Josh Steadmon <steadmon@google.com>,
git@vger.kernel.org, gitster@pobox.com, stolee@gmail.com,
peff@peff.net
Subject: Re: [PATCH v6 2/3] commit-graph: fix buffer read-overflow
Date: Wed, 20 Feb 2019 17:50:48 +0100 [thread overview]
Message-ID: <20190220165048.GR1622@szeder.dev> (raw)
In-Reply-To: <87d0nm5x1d.fsf@evledraar.gmail.com>
On Wed, Feb 20, 2019 at 03:55:58PM +0100, Ævar Arnfjörð Bjarmason wrote:
> > @@ -376,11 +377,15 @@ corrupt_graph_and_verify() {
> > data="${2:-\0}"
> > grepstr=$3
> > cd "$TRASH_DIRECTORY/full" &&
> > + orig_size=$(wc -c < $objdir/info/commit-graph) &&
> > + zero_pos=${4:-${orig_size}} &&
> > test_when_finished mv commit-graph-backup $objdir/info/commit-graph &&
> > cp $objdir/info/commit-graph commit-graph-backup &&
> > printf "$data" | dd of="$objdir/info/commit-graph" bs=1 seek="$pos" conv=notrunc &&
> > + dd of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=0 &&
> > + dd if=/dev/zero of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=$(($orig_size - $zero_pos)) &&
>
> In the limited time I had to dig it starts failing at test 46, when
> count=0 is given. dd on NetBSD exits with 127 when given count=0 it
> seems.
So the first 'dd' is supposed to truncate the commit-graph file at
$zero_pos. I don't think we need 'count=0' for that: in the absence
of the 'if=...' operand, 'dd' reads from standard input, which is
redirected from /dev/null in our test scripts, i.e. there is nothing
to read, and, consequently, there is nothing to write, either.
Though not strictly necessary, I would feel more comfortable if
'if=/dev/null' would be explicitly specified, and even more so with a
"# truncate at $zero_pos" comment above that command.
As to the second 'dd', I think we should not run it at all when count
would be zero, i.e. when $orig_size = $zero_pos, because in
combination with 'if=/dev/zero' it's asking for trouble. According to
POSIX [1]:
count=n
Copy only n input blocks. If n is zero, it is unspecified
whether no blocks or all blocks are copied.
Imagine a 'dd' that implements the second option: there are infinite
blocks in /dev/zero to copy! OTOH, if an implementation chooses the
first option (e.g. the usual Linux 'dd' from coreutils), then both of
these 'dd' invocations will leave the commit-graph file as-is, so it
doesn't matter whether we run them or not.
[1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/dd.html
next prev parent reply other threads:[~2019-02-20 16:50 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-05 22:32 [PATCH 0/2] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-05 22:32 ` [PATCH 1/2] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-05 22:48 ` Ævar Arnfjörð Bjarmason
2018-12-06 1:00 ` Josh Steadmon
2018-12-06 1:32 ` Junio C Hamano
2018-12-06 1:41 ` Junio C Hamano
2018-12-06 4:47 ` Junio C Hamano
2018-12-05 22:32 ` [PATCH 2/2] commit-graph: fix buffer read-overflow Josh Steadmon
2018-12-06 13:11 ` Derrick Stolee
2018-12-06 20:20 ` [PATCH v2 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-06 20:20 ` [PATCH v2 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-06 20:20 ` [PATCH v2 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2018-12-07 9:07 ` Jeff King
2018-12-07 13:33 ` Derrick Stolee
2018-12-06 20:20 ` [PATCH v2 3/3] Makefile: correct example fuzz build Josh Steadmon
2018-12-07 22:27 ` [PATCH v3 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-07 22:27 ` [PATCH v3 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-07 22:27 ` [PATCH v3 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2018-12-09 4:01 ` Junio C Hamano
2018-12-10 4:28 ` SZEDER Gábor
2018-12-10 21:58 ` Josh Steadmon
2018-12-10 21:56 ` Josh Steadmon
2018-12-11 9:50 ` Jeff King
2018-12-07 22:27 ` [PATCH v3 3/3] Makefile: correct example fuzz build Josh Steadmon
2018-12-13 19:43 ` [PATCH v4 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2018-12-13 19:43 ` [PATCH v4 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2018-12-13 19:43 ` [PATCH v4 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2019-01-12 10:57 ` SZEDER Gábor
2019-01-15 19:58 ` Josh Steadmon
2018-12-13 19:43 ` [PATCH v4 3/3] Makefile: correct example fuzz build Josh Steadmon
2018-12-18 17:35 ` [PATCH v4 0/3] Add commit-graph fuzzer and fix buffer overflow Jeff King
2018-12-18 21:05 ` Josh Steadmon
2018-12-19 15:51 ` Jeff King
2018-12-20 19:35 ` Johannes Schindelin
2018-12-20 20:11 ` Jeff King
2018-12-26 22:29 ` Junio C Hamano
2019-01-15 19:59 ` [PATCH v5 " Josh Steadmon
2019-01-15 19:59 ` [PATCH v5 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2019-01-15 20:33 ` Junio C Hamano
2019-01-15 19:59 ` [PATCH v5 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2019-01-15 19:59 ` [PATCH v5 3/3] Makefile: correct example fuzz build Josh Steadmon
2019-01-15 20:39 ` Junio C Hamano
2019-01-15 21:59 ` Josh Steadmon
2019-01-15 22:34 ` Junio C Hamano
2019-01-15 22:25 ` [PATCH v6 0/3] Add commit-graph fuzzer and fix buffer overflow Josh Steadmon
2019-01-15 22:25 ` [PATCH v6 1/3] commit-graph, fuzz: Add fuzzer for commit-graph Josh Steadmon
2019-01-15 22:25 ` [PATCH v6 2/3] commit-graph: fix buffer read-overflow Josh Steadmon
2019-02-20 14:55 ` Ævar Arnfjörð Bjarmason
2019-02-20 16:50 ` SZEDER Gábor [this message]
2019-01-15 22:25 ` [PATCH v6 3/3] Makefile: correct example fuzz build Josh Steadmon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190220165048.GR1622@szeder.dev \
--to=szeder.dev@gmail.com \
--cc=avarab@gmail.com \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=peff@peff.net \
--cc=steadmon@google.com \
--cc=stolee@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).