parse-options: fix memory leak when calling parse_options

call parse_options twice and occasionally meet unknown option
in the same place would cause memory leak, since the second `xstrdup`
in `parse_options_step` would make the first `xstrdup` unreachable.

One solution is allocate one more magic byte for the unknown option to
indicate that argv[?] stores a heap allocated arg. Assume for all
arg, `*((char *)arg - 1)` is valid, we could put a magic number before
the unknown option. Next time calling "xstrdup" will check the magic
number first, and frees the previous heap allocated memory.

Signed-off-by: Lidong Yan <[email protected]>

Author: brandb97

parse-options.c

@@ -886,6 +886,8 @@ enum parse_opt_result parse_options_step(struct parse_opt_ctx_t *ctx,
 					 const char * const usagestr[])
 {
 	int internal_help = !(ctx->flags & PARSE_OPT_NO_INTERNAL_HELP);
+	char *magic_ptr = NULL;
+	size_t opt_sz = 0;
 
 	/* we must reset ->opt, unknown short option leave it dangling */
 	ctx->opt = NULL;
@@ -981,7 +983,15 @@ enum parse_opt_result parse_options_step(struct parse_opt_ctx_t *ctx,
 					 *
 					 * This is leaky, too bad.
 					 */
-					ctx->argv[0] = xstrdup(ctx->opt - 1);
+					magic_ptr = (char *)ctx->argv[0] - 1;
+					if (*magic_ptr == OPT_MAGIC)
+						free(magic_ptr);
+					opt_sz = strlen(ctx->opt - 1) + 1;
+					magic_ptr = xmalloc(opt_sz + 1);
+					*magic_ptr = OPT_MAGIC;
+					ctx->argv[0] = magic_ptr + 1;
+					memcpy((char *)ctx->argv[0],
+					       ctx->opt - 1, opt_sz);
 					*(char *)ctx->argv[0] = '-';
 					goto unknown;
 				case PARSE_OPT_NON_OPTION:

parse-options.h

@@ -477,6 +477,8 @@ static inline void die_for_incompatible_opt2(int opt1, const char *opt1_name,
 		BUG("option callback expects an argument"); \
 } while(0)
 
+#define OPT_MAGIC ((char)(0xee))
+
 /*----- incremental advanced APIs -----*/
 
 struct parse_opt_cmdmode_list;