probe_utf8_pathname_composition: use internal strbuf

When we are initializing a .git directory, we may call
probe_utf8_pathname_composition to detect utf8 mangling. We
pass in a path buffer for it to use, and it blindly
strcpy()s into it, not knowing whether the buffer is large
enough to hold the result or not.

In practice this isn't a big deal, because the buffer we
pass in already contains "$GIT_DIR/config", and we append
only a few extra bytes to it. But we can easily do the right
thing just by calling git_path_buf ourselves. Technically
this results in a different pathname (before we appended our
utf8 characters to the "config" path, and now they get their
own files in $GIT_DIR), but that should not matter for our
purposes.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/init-db.c

@@ -312,7 +312,7 @@ static int create_default_files(const char *template_path)
 		strcpy(path + len, "CoNfIg");
 		if (!access(path, F_OK))
 			git_config_set("core.ignorecase", "true");
-		probe_utf8_pathname_composition(path, len);
+		probe_utf8_pathname_composition();
 	}
 
 	return reinit;

compat/precompose_utf8.c

@@ -36,24 +36,26 @@ static size_t has_non_ascii(const char *s, size_t maxlen, size_t *strlen_c)
 }
 
 
-void probe_utf8_pathname_composition(char *path, int len)
+void probe_utf8_pathname_composition(void)
 {
+	struct strbuf path = STRBUF_INIT;
 	static const char *auml_nfc = "\xc3\xa4";
 	static const char *auml_nfd = "\x61\xcc\x88";
 	int output_fd;
 	if (precomposed_unicode != -1)
 		return; /* We found it defined in the global config, respect it */
-	strcpy(path + len, auml_nfc);
-	output_fd = open(path, O_CREAT|O_EXCL|O_RDWR, 0600);
+	git_path_buf(&path, "%s", auml_nfc);
+	output_fd = open(path.buf, O_CREAT|O_EXCL|O_RDWR, 0600);
 	if (output_fd >= 0) {
 		close(output_fd);
-		strcpy(path + len, auml_nfd);
-		precomposed_unicode = access(path, R_OK) ? 0 : 1;
+		git_path_buf(&path, "%s", auml_nfd);
+		precomposed_unicode = access(path.buf, R_OK) ? 0 : 1;
 		git_config_set("core.precomposeunicode", precomposed_unicode ? "true" : "false");
-		strcpy(path + len, auml_nfc);
-		if (unlink(path))
-			die_errno(_("failed to unlink '%s'"), path);
+		git_path_buf(&path, "%s", auml_nfc);
+		if (unlink(path.buf))
+			die_errno(_("failed to unlink '%s'"), path.buf);
 	}
+	strbuf_release(&path);
 }
 
 

compat/precompose_utf8.h

@@ -27,7 +27,7 @@ typedef struct {
 } PREC_DIR;
 
 void precompose_argv(int argc, const char **argv);
-void probe_utf8_pathname_composition(char *, int);
+void probe_utf8_pathname_composition(void);
 
 PREC_DIR *precompose_utf8_opendir(const char *dirname);
 struct dirent_prec_psx *precompose_utf8_readdir(PREC_DIR *dirp);

git-compat-util.h

@@ -229,7 +229,7 @@ typedef unsigned long uintptr_t;
 #else
 #define precompose_str(in,i_nfd2nfc)
 #define precompose_argv(c,v)
-#define probe_utf8_pathname_composition(a,b)
+#define probe_utf8_pathname_composition()
 #endif
 
 #ifdef MKDIR_WO_TRAILING_SLASH