From: Junio C Hamano <gitster@pobox.com>
To: Jonathan Tan <jonathantanmy@google.com>
Cc: Marc Strapetz <marc.strapetz@syntevo.com>, git@vger.kernel.org
Subject: Re: [PATCH] packfile: avoid overflowing shift during decode
Date: Wed, 12 Jan 2022 12:12:34 -0800 [thread overview]
Message-ID: <xmqq4k68u30t.fsf@gitster.g> (raw)
In-Reply-To: <xmqq8rvku3bq.fsf@gitster.g> (Junio C. Hamano's message of "Wed, 12 Jan 2022 12:06:01 -0800")
Junio C Hamano <gitster@pobox.com> writes:
> Marc Strapetz <marc.strapetz@syntevo.com> writes:
>
>> On 11/11/2021 02:58, Junio C Hamano wrote:
>>> Jonathan Tan <jonathantanmy@google.com> writes:
>>>
>>>> diff --git a/packfile.c b/packfile.c
>>>> index 89402cfc69..972c327e29 100644
>>>> --- a/packfile.c
>>>> +++ b/packfile.c
>>>> @@ -1068,7 +1068,7 @@ unsigned long unpack_object_header_buffer(const unsigned char *buf,
>>>> size = c & 15;
>>>> shift = 4;
>>>> while (c & 0x80) {
>>>> - if (len <= used || bitsizeof(long) <= shift) {
>>>> + if (len <= used || (bitsizeof(long) - 7) <= shift) {
>>
>> This seems to cause troubles now for 32-bit systems (in my case Git
>> for Windows 32-Bit): `shift` will go through 4, 11, 18 and for 25 it
>> finally errors out. This means that objects >= 32MB can't be processed
>> anymore. The condition should probably be changed to:
>>
>> + if (len <= used || (bitsizeof(long) - 7) < shift) {
>>
>> This still ensures that the shift can never overflow and on 32-bit
>> systems restores the maximum size of 4G with a final shift of 127<<25
>> (the old condition `bitsizeof(long) <= shift` was perfectly valid for
>> 32-bit systems).
>
> Jonathan?
----- >8 --------- >8 --------- >8 --------- >8 --------- >8 -----
Date: Wed, 12 Jan 2022 12:11:42 -0800
Subject: [PATCH] packfile: fix off-by-one error in decoding logic
shift count being exactly at 7-bit smaller than the long is OK; on
32-bit architecture, shift count starts at 4 and goes through 11, 18
and 25, at which point the guard triggers one iteration too early.
Reported-by: Marc Strapetz <marc.strapetz@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
packfile.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/packfile.c b/packfile.c
index d3820c780b..667e21ce97 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1067,7 +1067,7 @@ unsigned long unpack_object_header_buffer(const unsigned char *buf,
size = c & 15;
shift = 4;
while (c & 0x80) {
- if (len <= used || (bitsizeof(long) - 7) <= shift) {
+ if (len <= used || (bitsizeof(long) - 7) < shift) {
error("bad object header");
size = used = 0;
break;
--
2.35.0-rc0-170-g6a31d082e5
next prev parent reply other threads:[~2022-01-12 20:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-10 23:40 [PATCH] packfile: avoid overflowing shift during decode Jonathan Tan
2021-11-11 1:58 ` Junio C Hamano
2022-01-10 23:22 ` Marc Strapetz
2022-01-12 20:06 ` Junio C Hamano
2022-01-12 20:12 ` Junio C Hamano [this message]
2022-01-12 20:27 ` Jonathan Tan
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=xmqq4k68u30t.fsf@gitster.g \
--to=gitster@pobox.com \
--cc=git@vger.kernel.org \
--cc=jonathantanmy@google.com \
--cc=marc.strapetz@syntevo.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).