Re: [PATCH 1/5] ref-cache: use 'size_t' instead of int for length

[Junio C Hamano <gitster@pobox.com>]

Karthik Nayak <karthik.188@gmail.com> writes:

> The commit 090eb5336c (refs: selectively set prefix in the seek
> functions, 2025-07-15) modified the ref-cache iterator to support
> seeking to a specified marker without setting the prefix.
>
> The commit adds and uses an integer 'len' to capture the length of the
> seek marker to compare with the entries of a given directory. Since the
> type of the variable is 'int', this is met with a typecast of converting
> a `strlen` to 'int' so it can be assigned to the 'len' variable.
>
> This is whole operation is a bit wrong:
> 1. Since the 'len' variable is eventually used in a 'strncmp', it should
> have been of type 'size_t'.
> 2. This also truncates the value provided from 'strlen' to an int, which
> could cause a large refname to produce a negative number.
>
> Let's do the correct thing here and simply use 'size_t' for `len`.
>
> Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
> ---
>  refs/ref-cache.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/refs/ref-cache.c b/refs/ref-cache.c
> index 1d95b56d40..8df7ae43e5 100644
> --- a/refs/ref-cache.c
> +++ b/refs/ref-cache.c
> @@ -498,13 +498,14 @@ static int cache_ref_iterator_seek(struct ref_iterator *ref_iterator,
>  		 * indexing to each level as needed.
>  		 */
>  		do {
> -			int len, idx;
> +			int idx;
> +			size_t len;
>  			int cmp = 0;
>  
>  			sort_ref_dir(dir);
>  
>  			slash = strchr(slash, '/');
> -			len = slash ? slash - refname : (int)strlen(refname);
> +			len = slash ? (size_t)(slash - refname) : strlen(refname);

The "strlen()" side is good, but was there recently a discussion on
how to safely convert (slash - refname) that is ptrdiff_t to size_t?

My archive search found a rather old ptrdiff_to_size() proposal
https://lore.kernel.org/git/20241227213729.GA796141@coredump.intra.peff.net/
but I thought there were another discussion thread about casting to size_t
recently.

I _think_ a vanilla cast is safe here, as slash sits always right to
refname (if not NULL, that is), and the difference should fit within
size_t (because the difference is smaller than the size of the
memory block pointed at by slash).

So in short, this looks good.  Will queue.