Subject: Re: [PATCH v2 4/4] apply: do not touch a file beyond a symbolic link

From: Junio C Hamano <[email-masked]>
Date: Tue, 03 Feb 2015 13:01:06 -0800

Jeff King <[email-masked]> writes:

> Here's the test addition I came up with, because it didn't look like we
> were covering this case. 

Thanks.

> diff --git a/t/t4122-apply-symlink-inside.sh b/t/t4122-apply-symlink-inside.sh
> index 942c5cb..fbba8dd 100755
> --- a/t/t4122-apply-symlink-inside.sh
> +++ b/t/t4122-apply-symlink-inside.sh
> @@ -89,6 +89,7 @@ test_expect_success SYMLINKS 'do not follow symbolic link (setup)' '
>  	rm -fr arch/x86_64/dir &&
>  
>  	cat add_symlink.patch add_file.patch >patch &&
> +	cat add_symlink.patch del_file.patch >tricky_del &&

This new patch

 (1) creates a symlink arch/x86_64/dir pointing at ../i386/dir
 (2) deletes arch/x86_64/dir/file

It can be a valid patch to be applied to a tree where arch/x86_64/dir/file
is in the index (either as a regular file, a symlink, or even a submodule)
and nothing else is in arch/x86_64/dir directory.

> @@ -112,6 +113,20 @@ test_expect_success SYMLINKS 'do not follow symbolic link (same input)' '
>  	test_i18ngrep "beyond a symbolic link" error-ct &&
>  	test_must_fail git ls-files --error-unmatch arch/x86_64/dir &&
>  	test_must_fail git ls-files --error-unmatch arch/i386/dir
> +
> +	>arch/i386/dir/file &&
> +	git add arch/i386/dir/file &&

At this point, the target of the patch application has:

	arch/i386/boot/Makefile
	arch/i386/dir/file
	arch/x86_64/boot/Makefile

all of which are regular files.  The index and the working tree
match.

> +	test_must_fail git apply tricky_del &&

The reason why this does not apply has nothing to do with the topic
of this series, I think.  It wants to delete arch/x86_64/dir/file,
which does not exist in the target, and the patch is rejected.

It is a good test to make sure that we do not "incrementally" apply
and get fooled by arch/x86_64/dir that will become a symbolic link,
making arch/x86_64/dir/file to appear as arch/i386/dir/file that
does exist in the preimage.

> +	test_path_is_file arch/i386/dir/file &&

When we reject the entire patch, we do so without touching the
outside world, of course ;-), which is good.

> +	test_must_fail git apply --index tricky_del &&
> +	test_path_is_file arch/i386/dir/file &&
> +	test_must_fail git ls-files --error-unmatch arch/x86_64/dir &&
> +	git ls-files --error-unmatch arch/i386/dir &&
> +
> +	test_must_fail git apply --cached tricky_del &&
> +	test_must_fail git ls-files --error-unmatch arch/x86_64/dir &&
> +	git ls-files --error-unmatch arch/i386/dir
>  '

In both of the above, "git apply" rejects its input for the same
reason.  The file it wants to remove does not exist in the target.

>  test_expect_success SYMLINKS 'do not follow symbolic link (existing)' '
> @@ -125,6 +140,7 @@ test_expect_success SYMLINKS 'do not follow symbolic link (existing)' '
>  	test_i18ngrep "beyond a symbolic link" error-wt-add &&
>  	test_path_is_missing arch/i386/dir/file &&
>  
> +	mkdir arch/i386/dir &&

Thanks for spotting this one ;-)

>  	>arch/i386/dir/file &&
>  	test_must_fail git apply del_file.patch 2>error-wt-del &&

del_file.patch wants to remove arch/x86_64/dir/file, and arch/x86_64/dir
is a symbolic link to ../i386/dir in the target at this point, so it
is trying to delete beyond the symbolic link, which gets rejected by
this series.  Good.

>  	test_i18ngrep "beyond a symbolic link" error-wt-del &&