exec: cleanup the CONFIG_MODULES logic

search_binary_handler() uses "for (try=0; try<2; try++)" to avoid "goto"
but the code looks too complicated and horrible imho.  We still need to
check "try == 0" before request_module() and add the additional "break"
for !CONFIG_MODULES case.

Kill this loop and use a simple "bool need_retry" + "goto retry".  The
code looks much simpler and we do not even need ifdef's, gcc can optimize
out the "if (need_retry)" block if !IS_ENABLED().
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NKees Cook <keescook@chromium.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Zach Levis <zml@linux.vnet.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1367,13 +1367,15 @@ int remove_arg_zero(struct linux_binprm *bprm)
 }
 EXPORT_SYMBOL(remove_arg_zero);
 
+#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
 /*
  * cycle the list of binary formats handler, until one recognizes the image
  */
 int search_binary_handler(struct linux_binprm *bprm)
 {
-	int try, retval;
+	bool need_retry = IS_ENABLED(CONFIG_MODULES);
 	struct linux_binfmt *fmt;
+	int retval;
 
 	/* This allows 4 levels of binfmt rewrites before failing hard. */
 	if (bprm->recursion_depth > 5)
@@ -1388,7 +1390,7 @@ int search_binary_handler(struct linux_binprm *bprm)
 		return retval;
 
 	retval = -ENOENT;
-	for (try=0; try<2; try++) {
+ retry:
 	read_lock(&binfmt_lock);
 	list_for_each_entry(fmt, &formats, lh) {
 		if (!try_module_get(fmt->module))
@@ -1411,24 +1413,16 @@ int search_binary_handler(struct linux_binprm *bprm)
 		}
 	}
 	read_unlock(&binfmt_lock);
-#ifdef CONFIG_MODULES
-		if (retval != -ENOEXEC || bprm->mm == NULL) {
-			break;
-		} else {
-#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
-			if (printable(bprm->buf[0]) &&
-			    printable(bprm->buf[1]) &&
-			    printable(bprm->buf[2]) &&
-			    printable(bprm->buf[3]))
-				break; /* -ENOEXEC */
-			if (try)
-				break; /* -ENOEXEC */
-			request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
-		}
-#else
-		break;
-#endif
+
+	if (need_retry && retval == -ENOEXEC && bprm->mm) {
+		if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
+		    printable(bprm->buf[2]) && printable(bprm->buf[3]))
+			return retval;
+		request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2));
+		need_retry = false;
+		goto retry;
 	}
+
 	return retval;
 }
 EXPORT_SYMBOL(search_binary_handler);