Re: [PATCH 10/11] config: fix a leak in git_config_copy_or_rename_section_in_file

[Rubén Justo <rjusto@xxxxxxxxx>]

On 12-jun-2023 00:05:18, Jeff King wrote:
> On Sun, Jun 11, 2023 at 08:50:45PM +0200, Rubén Justo wrote:
> 
> > diff --git a/config.c b/config.c
> > index 39a7d7422c..207e4394a3 100644
> > --- a/config.c
> > +++ b/config.c
> > @@ -3833,6 +3833,7 @@ static int git_config_copy_or_rename_section_in_file(const char *config_filename
> >  						output[0] = '\t';
> >  					}
> >  				} else {
> > +					strbuf_release(&copystr);
> >  					copystr = store_create_section(new_name, &store);
> >  				}
> >  			}
> 
> Wow, I did a double-take on this code. It is uncommon in our codebase to
> assign a struct by value in a function return like this, and doubly
> weird to assign a strbuf (since the whole point of strbuf is to use the
> opaque functions to make sure we aren't overwriting existing allocations
> or aliasing pointers).
> 
> I think your fix here is the correct thing if we aren't going to clean
> up the code further.
> 
> The more usual thing for our codebase would be refactoring like:
> 
> diff --git a/config.c b/config.c
> index b79baf83e3..f5a7cced7c 100644
> --- a/config.c
> +++ b/config.c
> @@ -3140,37 +3140,36 @@ static int write_error(const char *filename)
>  	return 4;
>  }
>  
> -static struct strbuf store_create_section(const char *key,
> -					  const struct config_store_data *store)
> +static void store_create_section(const char *key,
> +				 const struct config_store_data *store,
> +				 struct strbuf *sb)
>  {
>  	const char *dot;
>  	size_t i;
> -	struct strbuf sb = STRBUF_INIT;
>  
>  	dot = memchr(key, '.', store->baselen);
>  	if (dot) {
> -		strbuf_addf(&sb, "[%.*s \"", (int)(dot - key), key);
> +		strbuf_addf(sb, "[%.*s \"", (int)(dot - key), key);
>  		for (i = dot - key + 1; i < store->baselen; i++) {
>  			if (key[i] == '"' || key[i] == '\\')
> -				strbuf_addch(&sb, '\\');
> -			strbuf_addch(&sb, key[i]);
> +				strbuf_addch(sb, '\\');
> +			strbuf_addch(sb, key[i]);
>  		}
> -		strbuf_addstr(&sb, "\"]\n");
> +		strbuf_addstr(sb, "\"]\n");
>  	} else {
> -		strbuf_addch(&sb, '[');
> -		strbuf_add(&sb, key, store->baselen);
> -		strbuf_addstr(&sb, "]\n");
> +		strbuf_addch(sb, '[');
> +		strbuf_add(sb, key, store->baselen);
> +		strbuf_addstr(sb, "]\n");
>  	}
> -
> -	return sb;
>  }
>  
>  static ssize_t write_section(int fd, const char *key,
>  			     const struct config_store_data *store)
>  {
> -	struct strbuf sb = store_create_section(key, store);
> +	struct strbuf sb = STRBUF_INIT;
>  	ssize_t ret;
>  
> +	store_create_section(key, store, &sb);
>  	ret = write_in_full(fd, sb.buf, sb.len);
>  	strbuf_release(&sb);
>  
> @@ -3833,7 +3832,9 @@ static int git_config_copy_or_rename_section_in_file(const char *config_filename
>  						output[0] = '\t';
>  					}
>  				} else {
> -					copystr = store_create_section(new_name, &store);
> +					strbuf_reset(&copystr);
> +					store_create_section(new_name, &store,
> +							     &copystr);
>  				}
>  			}
>  			remove = 0;

I have a draft with the exact same change.  I chose the simple fix,
though.  I wasn't expecting your review :)

I'll definitely re-roll with this.

Thanks!