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From: Junio C Hamano <gitster@pobox.com>
To: "Michał Górny" <mgorny@gentoo.org>
Cc: git@vger.kernel.org
Subject: Re: [PATCH v4] gpg-interface.c: detect and reject multiple signatures on commits
Date: Sun, 21 Oct 2018 08:57:36 +0900	[thread overview]
Message-ID: <xmqqin1wyxvz.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20181020193020.28517-1-mgorny@gentoo.org> ("Michał Górny"'s message of "Sat, 20 Oct 2018 21:30:20 +0200")

Michał Górny <mgorny@gentoo.org> writes:

> GnuPG supports creating signatures consisting of multiple signature
> packets.  If such a signature is verified, it outputs all the status
> messages for each signature separately.  However, git currently does not
> account for such scenario and gets terribly confused over getting
> multiple *SIG statuses.
>
> For example, if a malicious party alters a signed commit and appends
> a new untrusted signature, git is going to ignore the original bad
> signature and report untrusted commit instead.  However, %GK and %GS
> format strings may still expand to the data corresponding
> to the original signature, potentially tricking the scripts into
> trusting the malicious commit.
>
> Given that the use of multiple signatures is quite rare, git does not
> support creating them without jumping through a few hoops, and finally
> supporting them properly would require extensive API improvement, it
> seems reasonable to just reject them at the moment.
>
> Signed-off-by: Michał Górny <mgorny@gentoo.org>
> ---
>  gpg-interface.c          | 90 +++++++++++++++++++++++++++-------------
>  t/t7510-signed-commit.sh | 26 ++++++++++++
>  2 files changed, 87 insertions(+), 29 deletions(-)
>
> Changes in v4:
> * switched to using skip_prefix(),
> * renamed the variable to seen_exclusive_status,
> * made the loop terminate early on first duplicate status seen.

Thanks for sticking to the topic and polishing it further.  Looks
very good.  

Will replace.

> +	int seen_exclusive_status = 0;
> +
> +	/* Iterate over all lines */
> +	for (line = buf; *line; line = strchrnul(line+1, '\n')) {
> +		while (*line == '\n')
> +			line++;
> +		/* Skip lines that don't start with GNUPG status */
> +		if (!skip_prefix(line, "[GNUPG:] ", &line))
> +			continue;
> +
> +		/* Iterate over all search strings */
> +		for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
> +			if (skip_prefix(line, sigcheck_gpg_status[i].check, &line)) {
> +				if (sigcheck_gpg_status[i].flags & GPG_STATUS_EXCLUSIVE) {
> +					if (++seen_exclusive_status > 1)
> +						goto found_duplicate_status;

Very minor point but by not using pre-increment, i.e.

		if (seen_exclusive_status++)
			goto found_duplicate_status;

you can use the expression as a "have we already seen?" boolean,
whic may probably be more idiomatic.

The patch is good in the way written as-is, and this is so minor
that it is not worth rerolling to only update this part.

Thanks.


  reply	other threads:[~2018-10-20 23:57 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-20 19:30 [PATCH v4] gpg-interface.c: detect and reject multiple signatures on commits Michał Górny
2018-10-20 23:57 ` Junio C Hamano [this message]
2018-10-21  7:10   ` Michał Górny
2018-10-22  0:58     ` Junio C Hamano
2018-10-22  8:04   ` Michał Górny
2018-10-22 15:25     ` Michał Górny
2018-11-03 15:17 ` Duy Nguyen
2018-11-03 15:32   ` Michał Górny
2018-11-03 15:36     ` Duy Nguyen
2018-11-03 15:58       ` Michał Górny
2018-11-03 15:42     ` Duy Nguyen

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