From: Junio C Hamano <gitster@pobox•com>
To: Dennis Kaarsemaker <dennis@kaarsemaker•net>
Cc: git@vger•kernel.org, pclouds@gmail•com
Subject: Re: [PATCH] reflog-walk: don't segfault on non-commit sha1's in the reflog
Date: Wed, 30 Dec 2015 13:41:54 -0800 [thread overview]
Message-ID: <xmqq1ta3ehr1.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <1451511208.9251.21.camel@kaarsemaker.net> (Dennis Kaarsemaker's message of "Wed, 30 Dec 2015 22:33:28 +0100")
Dennis Kaarsemaker <dennis@kaarsemaker•net> writes:
> On wo, 2015-12-30 at 13:20 -0800, Junio C Hamano wrote:
>> Dennis Kaarsemaker <dennis@kaarsemaker•net> writes:
>>
>> > diff --git a/reflog-walk.c b/reflog-walk.c
>> > index 85b8a54..b85c8e8 100644
>> > --- a/reflog-walk.c
>> > +++ b/reflog-walk.c
>> > @@ -236,8 +236,8 @@ void fake_reflog_parent(struct reflog_walk_info
>> > *info, struct commit *commit)
>> > reflog = &commit_reflog->reflogs->items[commit_reflog
>> > ->recno];
>> > info->last_commit_reflog = commit_reflog;
>> > commit_reflog->recno--;
>> > - commit_info->commit = (struct commit *)parse_object(reflog
>> > ->osha1);
>> > - if (!commit_info->commit) {
>> > + commit_info->commit = lookup_commit(reflog->osha1);
>> > + if (!commit_info->commit || parse_commit(commit_info
>> > ->commit)) {
>> > commit->parents = NULL;
>> > return;
>>
>> This looks somewhat roundabout and illogical. The original was bad
>> because it blindly assumed reflgo->osha1 refers to a commit without
>> making sure that assumption holds. Calling lookup_commit() blindly
>> is not much better, even though you are helped that the function
>> happens not to barf if the given object is not a commit.
>>
>> Also this changes semantics, no? Trace the original flow and think
>> what happens, when we see a commit object that cannot be parsed in
>> parse_commit_buffer(). parse_object() calls parse_object_buffer()
>> which in turn calls parse_commit_buffer() and the entire callchain
>> returns NULL. commit_info->commit will become NULL in such a case.
>>
>> With your code, lookup_commit() will store a non NULL in
>> commit_info->commit, and parse_commit() calls parse_commit_buffer()
>> and that would fail, so you clear commit->parents to NULL but fail
>> to set commit_info->commit to NULL.
>>
>> Why not keep the parse_object() as-is and make sure we error out
>> unless the result is a commit with a more explicit check, perhaps
>> like this, instead?
>
> lookup_commit actually returns NULL (via object_as_type) for objects
> that are not commits, so I don't think the above is true.
I think you did not read what you are responding to. I was talking
about the error case where the object _is_ a commit (hence lookup
returns it), but parse_commit_buffer() does not like its contents.
> The code below also loses the diagnostic message about the object
> not being a commit.
Giving such a diagnostic message is a BUG.
A ref can legitimately point at any type of object (only refs under
refs/heads/, aka "branches", must point at commits), so you MUST NOT
complain about seeing a non-commit in a reflog in general.
next prev parent reply other threads:[~2015-12-30 21:42 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-30 9:24 Segfault in git reflog Dennis Kaarsemaker
2015-12-30 10:31 ` Duy Nguyen
2015-12-30 11:17 ` Dennis Kaarsemaker
2015-12-30 11:26 ` Duy Nguyen
2015-12-30 11:28 ` Duy Nguyen
2015-12-30 12:28 ` Dennis Kaarsemaker
2015-12-30 13:19 ` Duy Nguyen
2015-12-30 15:22 ` [PATCH] reflog-walk: don't segfault on non-commit sha1's in the reflog Dennis Kaarsemaker
2015-12-30 21:20 ` Junio C Hamano
2015-12-30 21:33 ` Dennis Kaarsemaker
2015-12-30 21:41 ` Junio C Hamano [this message]
2015-12-30 21:49 ` Dennis Kaarsemaker
2015-12-30 22:17 ` [PATCH v2] " Dennis Kaarsemaker
2015-12-30 22:42 ` Junio C Hamano
2015-12-30 23:33 ` [PATCH v3] " Dennis Kaarsemaker
2015-12-31 0:02 ` Junio C Hamano
2015-12-31 8:57 ` Dennis Kaarsemaker
2015-12-31 15:43 ` Dennis Kaarsemaker
2016-01-05 21:12 ` [PATCH v4] " Dennis Kaarsemaker
2016-01-06 1:05 ` Eric Sunshine
2016-01-06 1:20 ` Dennis Kaarsemaker
2016-01-06 1:28 ` Eric Sunshine
2016-01-06 1:52 ` Eric Sunshine
2016-01-06 9:13 ` Dennis Kaarsemaker
2016-01-06 9:30 ` Duy Nguyen
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