Re: [PATCH v6 01/10] fsmonitor: fix khash memory leak in do_handle_client

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

"Paul Tarjan via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Paul Tarjan <github@paulisageek.com>
>
> The `shown` kh_str_t was freed with kh_release_str() at a point in
> the code only reachable in the non-trivial response path.  When the
> client receives a trivial response, the code jumps to the `cleanup`
> label, skipping the kh_release_str() call entirely and leaking the
> hash table.
>
> Fix this by initializing `shown` to NULL and moving the cleanup to the
> `cleanup` label using kh_destroy_str(), which is safe to call on NULL.
> This ensures the hash table is freed regardless of which code path is
> taken.

Makes perfect sense, the changes to the code matches the
description, and the difference between kh_release_* and
kh_destroy_* in khash.h is exactly as described in the log message.

Perfect.  I wish all the patches posted here are as easy to review
as this one ;-)

> Signed-off-by: Paul Tarjan <github@paulisageek.com>
> ---
>  builtin/fsmonitor--daemon.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/fsmonitor--daemon.c b/builtin/fsmonitor--daemon.c
> index 242c594646..bc4571938c 100644
> --- a/builtin/fsmonitor--daemon.c
> +++ b/builtin/fsmonitor--daemon.c
> @@ -671,7 +671,7 @@ static int do_handle_client(struct fsmonitor_daemon_state *state,
>  	const struct fsmonitor_batch *batch;
>  	struct fsmonitor_batch *remainder = NULL;
>  	intmax_t count = 0, duplicates = 0;
> -	kh_str_t *shown;
> +	kh_str_t *shown = NULL;
>  	int hash_ret;
>  	int do_trivial = 0;
>  	int do_flush = 0;
> @@ -909,8 +909,6 @@ static int do_handle_client(struct fsmonitor_daemon_state *state,
>  		total_response_len += payload.len;
>  	}
>  
> -	kh_release_str(shown);
> -
>  	pthread_mutex_lock(&state->main_lock);
>  
>  	if (token_data->client_ref_count > 0)
> @@ -954,6 +952,7 @@ static int do_handle_client(struct fsmonitor_daemon_state *state,
>  	trace2_data_intmax("fsmonitor", the_repository, "response/count/duplicates", duplicates);
>  
>  cleanup:
> +	kh_destroy_str(shown);
>  	strbuf_release(&response_token);
>  	strbuf_release(&requested_token_id);
>  	strbuf_release(&payload);