parse-options: don't leak alias help messages

preprocess_options() allocates new strings for help messages for
OPTION_ALIAS. Therefore we also need to clean those help messages up
when freeing the returned options.

First introduced in:
  7c28058 (parse-options: teach "git cmd -h" to show alias as alias, 2020-03-16)

The preprocessed options themselves no longer contain any indication
that a given option is/was an alias: the easiest and fastest way to
figure it out is to look back at the original options. Alternatively we
could iterate over the alias_groups list - but that would require nested
looping and is likely to be a (little) less efficient.

As far as I can tell, parse_options() is only ever used once per
command, and the help messages are small - hence this leak has very
little impact.

This leak was found while running t0001. LSAN output can be found below:

Direct leak of 65 byte(s) in 1 object(s) allocated from:
    #0 0x49a859 in realloc /home/abuild/rpmbuild/BUILD/llvm-11.0.0.src/build/../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:164:3
    #1 0x9aae36 in xrealloc /home/ahunt/oss-fuzz/git/wrapper.c:126:8
    #2 0x939d8d in strbuf_grow /home/ahunt/oss-fuzz/git/strbuf.c:98:2
    #3 0x93b936 in strbuf_vaddf /home/ahunt/oss-fuzz/git/strbuf.c:392:3
    #4 0x93b7ff in strbuf_addf /home/ahunt/oss-fuzz/git/strbuf.c:333:2
    #5 0x86747e in preprocess_options /home/ahunt/oss-fuzz/git/parse-options.c:666:3
    #6 0x866ed2 in parse_options /home/ahunt/oss-fuzz/git/parse-options.c:847:17
    #7 0x51c4a7 in cmd_clone /home/ahunt/oss-fuzz/git/builtin/clone.c:989:9
    #8 0x4cd60d in run_builtin /home/ahunt/oss-fuzz/git/git.c:453:11
    #9 0x4cb2da in handle_builtin /home/ahunt/oss-fuzz/git/git.c:704:3
    #10 0x4ccc37 in run_argv /home/ahunt/oss-fuzz/git/git.c:771:4
    #11 0x4cac29 in cmd_main /home/ahunt/oss-fuzz/git/git.c:902:19
    #12 0x69c9fe in main /home/ahunt/oss-fuzz/git/common-main.c:52:11
    #13 0x7fdac42d4349 in __libc_start_main (/lib64/libc.so.6+0x24349)

Signed-off-by: Andrzej Hunt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ahunt

parse-options.c

@@ -625,6 +625,8 @@ static int show_gitcomp(const struct option *opts, int show_all)
  *
  * Right now this is only used to preprocess and substitute
  * OPTION_ALIAS.
+ *
+ * The returned options should be freed using free_preprocessed_options.
  */
 static struct option *preprocess_options(struct parse_opt_ctx_t *ctx,
 					 const struct option *options)
@@ -693,6 +695,21 @@ static struct option *preprocess_options(struct parse_opt_ctx_t *ctx,
 	return newopt;
 }
 
+static void free_preprocessed_options(const struct option ** preprocessed_options, const struct option *original_options)
+{
+	int i;
+
+	if (!*preprocessed_options) {
+		return;
+	}
+	for (i = 0; original_options[i].type != OPTION_END; i++) {
+		if (original_options[i].type == OPTION_ALIAS) {
+			free((void *)(*preprocessed_options)[i].help);
+		}
+	}
+	free((void *)*preprocessed_options);
+}
+
 static int usage_with_options_internal(struct parse_opt_ctx_t *,
 				       const char * const *,
 				       const struct option *, int, int);
@@ -838,15 +855,17 @@ int parse_options(int argc, const char **argv, const char *prefix,
 		  int flags)
 {
 	struct parse_opt_ctx_t ctx;
-	struct option *real_options;
+	const struct option *preprocessed_options, *original_options = NULL;
 
 	disallow_abbreviated_options =
 		git_env_bool("GIT_TEST_DISALLOW_ABBREVIATED_OPTIONS", 0);
 
 	memset(&ctx, 0, sizeof(ctx));
-	real_options = preprocess_options(&ctx, options);
-	if (real_options)
-		options = real_options;
+	preprocessed_options = preprocess_options(&ctx, options);
+	if (preprocessed_options) {
+		original_options = options;
+		options = preprocessed_options;
+	}
 	parse_options_start_1(&ctx, argc, argv, prefix, options, flags);
 	switch (parse_options_step(&ctx, options, usagestr)) {
 	case PARSE_OPT_HELP:
@@ -870,7 +889,7 @@ int parse_options(int argc, const char **argv, const char *prefix,
 	}
 
 	precompose_argv_prefix(argc, argv, NULL);
-	free(real_options);
+	free_preprocessed_options(&preprocessed_options, original_options);
 	free(ctx.alias_groups);
 	return parse_options_end(&ctx);
 }