Re: [PATCH v5] diff: make diff_free_filespec_data accept NULL

> Hi Jinoh,
>
> On Wed, 11 Nov 2020, Jinoh Kang wrote:
>
>> diff_free_filespec_data crashes when passed a NULL fillspec pointer.
>> Commit 3aef54e8b8 ("diff: munmap() file contents before running external
>> diff", 2019-07-11) introduced calls to diff_free_filespec_data in
>> run_external_diff without also checking if the argument is NULL.
>>
>> Git uses NULL filespecs to indicate unmerged files when merge conflict
>> resolution is in progress.  Fortunately, other code paths bail out early
>> even before NULL can reach diff_free_filespec_data(); however, difftool
>> is expected to do a full-blown diff anyway regardless of conflict
>> status.
>>
>> Fix this and prevent any similar bugs in the future by making
>> `diff_free_filespec_data(NULL)` a no-op.
>>
>> Add a test case that confirms that running difftool --cached with
>> unmerged files does not result in a SIGSEGV.
>>
>> Signed-off-by: Jinoh Kang <luke1337@theori.io>
>
> ACK!
>
> The patch looks good to go to me.
>
> Thank you!
> Dscho

>
>> ---
>>  diff.c              |  3 +++
>>  t/t7800-difftool.sh | 13 +++++++++++++
>>  2 files changed, 16 insertions(+)
>>
>> diff --git a/diff.c b/diff.c
>> index d24f47df99..ace4a1d387 100644
>> --- a/diff.c
>> +++ b/diff.c
>> @@ -4115,6 +4115,9 @@ void diff_free_filespec_blob(struct diff_filespec *s)
>>
>>  void diff_free_filespec_data(struct diff_filespec *s)
>>  {
>> +	if (!s)
>> +		return;
>> +
>>  	diff_free_filespec_blob(s);
>>  	FREE_AND_NULL(s->cnt_data);
>>  }
>> diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
>> index 524f30f7dc..a578b35761 100755
>> --- a/t/t7800-difftool.sh
>> +++ b/t/t7800-difftool.sh
>> @@ -728,6 +728,19 @@ test_expect_success 'add -N and difftool -d' '
>>  	git difftool --dir-diff --extcmd ls
>>  '
>>
>> +test_expect_success 'difftool --cached with unmerged files' '
>> +	test_when_finished git reset --hard &&
>> +
>> +	test_commit conflicting &&
>> +	test_commit conflict-a conflict.t a &&
>> +	git reset --hard conflicting &&
>> +	test_commit conflict-b conflict.t b &&
>> +	test_must_fail git merge conflict-a &&
>> +
>> +	git difftool --cached --no-prompt >output &&
>> +	test_must_be_empty output
>> +'
>> +
>>  test_expect_success 'outside worktree' '
>>  	echo 1 >1 &&
>>  	echo 2 >2 &&
>> --
>> 2.26.2
>>
>>