Re: [PATCH v2 6/8] dir: fix checks on common prefix directory

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Elijah,

I have not had time to dive deeply into this, but I know that it _does_
cause a ton of segmentation faults in the `shears/pu` branch (where all of
Git for Windows' patches are rebased on top of `pu`):

On Tue, 10 Dec 2019, Elijah Newren via GitGitGadget wrote:

> diff --git a/dir.c b/dir.c
> index 645b44ea64..9c71a9ac21 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -2102,37 +2102,69 @@ static int treat_leading_path(struct dir_struct *dir,
>  			      const struct pathspec *pathspec)
>  {
>  	struct strbuf sb = STRBUF_INIT;
> -	int baselen, rc = 0;
> +	int prevlen, baselen;
>  	const char *cp;
> +	struct cached_dir cdir;
> +	struct dirent de;
> +	enum path_treatment state = path_none;
> +
> +	/*
> +	 * For each directory component of path, we are going to check whether
> +	 * that path is relevant given the pathspec.  For example, if path is
> +	 *    foo/bar/baz/
> +	 * then we will ask treat_path() whether we should go into foo, then
> +	 * whether we should go into bar, then whether baz is relevant.
> +	 * Checking each is important because e.g. if path is
> +	 *    .git/info/
> +	 * then we need to check .git to know we shouldn't traverse it.
> +	 * If the return from treat_path() is:
> +	 *    * path_none, for any path, we return false.
> +	 *    * path_recurse, for all path components, we return true
> +	 *    * <anything else> for some intermediate component, we make sure
> +	 *        to add that path to the relevant list but return false
> +	 *        signifying that we shouldn't recurse into it.
> +	 */
>
>  	while (len && path[len - 1] == '/')
>  		len--;
>  	if (!len)
>  		return 1;
> +
> +	memset(&cdir, 0, sizeof(cdir));
> +	memset(&de, 0, sizeof(de));
> +	cdir.de = &de;
> +	de.d_type = DT_DIR;

So here, `de` is zeroed out, and therefore `de.d_name` is `NULL`.

>  	baselen = 0;
> +	prevlen = 0;
>  	while (1) {
> -		cp = path + baselen + !!baselen;
> +		prevlen = baselen + !!baselen;
> +		cp = path + prevlen;
>  		cp = memchr(cp, '/', path + len - cp);
>  		if (!cp)
>  			baselen = len;
>  		else
>  			baselen = cp - path;
> -		strbuf_setlen(&sb, 0);
> +		strbuf_reset(&sb);
>  		strbuf_add(&sb, path, baselen);
>  		if (!is_directory(sb.buf))
>  			break;
> -		if (simplify_away(sb.buf, sb.len, pathspec))
> -			break;
> -		if (treat_one_path(dir, NULL, istate, &sb, baselen, pathspec,
> -				   DT_DIR, NULL) == path_none)
> +		strbuf_reset(&sb);
> +		strbuf_add(&sb, path, prevlen);
> +		memcpy(de.d_name, path+prevlen, baselen-prevlen);

But here we try to copy a path into that `de.d_name`, which is still
`NULL`?

That can't be right, can it?

Thanks for your help,
Dscho

> +		de.d_name[baselen-prevlen] = '\0';
> +		state = treat_path(dir, NULL, &cdir, istate, &sb, prevlen,
> +				    pathspec);
> +		if (state != path_recurse)
>  			break; /* do not recurse into it */
> -		if (len <= baselen) {
> -			rc = 1;
> +		if (len <= baselen)
>  			break; /* finished checking */
> -		}
>  	}
> +	add_path_to_appropriate_result_list(dir, NULL, &cdir, istate,
> +					    &sb, baselen, pathspec,
> +					    state);
> +
>  	strbuf_release(&sb);
> -	return rc;
> +	return state == path_recurse;
>  }
>
>  static const char *get_ident_string(void)
> diff --git a/t/t3011-common-prefixes-and-directory-traversal.sh b/t/t3011-common-prefixes-and-directory-traversal.sh
> index d6e161ddd8..098fddc75b 100755
> --- a/t/t3011-common-prefixes-and-directory-traversal.sh
> +++ b/t/t3011-common-prefixes-and-directory-traversal.sh
> @@ -74,7 +74,7 @@ test_expect_success 'git ls-files -o --directory untracked_dir does not recurse'
>  	test_cmp expect actual
>  '
>
> -test_expect_failure 'git ls-files -o --directory untracked_dir/ does not recurse' '
> +test_expect_success 'git ls-files -o --directory untracked_dir/ does not recurse' '
>  	echo untracked_dir/ >expect &&
>  	git ls-files -o --directory untracked_dir/ >actual &&
>  	test_cmp expect actual
> @@ -86,7 +86,7 @@ test_expect_success 'git ls-files -o untracked_repo does not recurse' '
>  	test_cmp expect actual
>  '
>
> -test_expect_failure 'git ls-files -o untracked_repo/ does not recurse' '
> +test_expect_success 'git ls-files -o untracked_repo/ does not recurse' '
>  	echo untracked_repo/ >expect &&
>  	git ls-files -o untracked_repo/ >actual &&
>  	test_cmp expect actual
> @@ -133,7 +133,7 @@ test_expect_success 'git ls-files -o .git shows nothing' '
>  	test_must_be_empty actual
>  '
>
> -test_expect_failure 'git ls-files -o .git/ shows nothing' '
> +test_expect_success 'git ls-files -o .git/ shows nothing' '
>  	git ls-files -o .git/ >actual &&
>  	test_must_be_empty actual
>  '
> --
> gitgitgadget
>
>
>