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

[Jeff King <peff@xxxxxxxx>]

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;