Hello dear GRUB developers,
I recently came across a strange behavior of GRUB2:
Calling grub_printf with an 80 character string (grub_printf(str) == 80)
80 times in a row leads to grub being unresponsive and de facto being
trapped in endless loop (of printing newlines?).
This behavior does not occur before switching to normal mode, when
grub_printf still calls grub_xputs_dumb. It only occurs after switching
to normal mode, when grub_printf calls grub_xputs_normal.
The bug is not triggered, if 80*80 (or more) characters are being
printed at once by grub_printf:
A string of at least 80 characters has to be grub_printf'd at least 80
times in a row.
I attached a small patch to demonstrate the bug:
- printf_test prints an 80-char long string 80 times successively
- this test succeeds with grub_printf using grub_xputs_dumb (before
normal mode)
- this test fails with grub_printf using grub_xputs_normal (after
switching to normal mode)
I could reproduce this behavior within qemu and on several different
physical systems. For testing, I used the current master-branch and
grub-2.02-rc2 (8014b7b), but prior versions are affected too probably.
Best regards,
Stephan
From 8a21e144819113ca222090a08dc4e04a8faad58b Mon Sep 17 00:00:00 2001
From: root <root@localhost>
Date: Fri, 19 Jul 2019 09:30:39 +0000
Subject: [PATCH 1/1] Bug in grub_xputs_normal
---
grub-core/normal/main.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/grub-core/normal/main.c b/grub-core/normal/main.c
index 1b03dfd57..0442c9cd7 100644
--- a/grub-core/normal/main.c
+++ b/grub-core/normal/main.c
@@ -33,6 +33,34 @@
#include <grub/charset.h>
#include <grub/script_sh.h>
#include <grub/bufio.h>
+#include <grub/time.h>
+
+/* FIXME
+ *
+ * printf_test succeeds with grub_printf using grub_xputs_dumb (before normal
+ * mode), but fails with grub_printf using grub_xputs_normal (after switching
+ * to normal mode).
+ *
+ * the buggy behavior occurs when
+ * - grub_strlen(buffer) >= 80, AND
+ * - buffer printed 80 times successively
+ */
+
+static void
+printf_test(const char print_char)
+{
+ char buffer[80+1];
+ unsigned int idx;
+ unsigned int print_counter;
+
+ /* fill buffer with print_char */
+ for (idx = 0; idx < sizeof(buffer) - 1; idx++)
+ buffer[idx] = print_char;
+ buffer[idx] = '\0';
+
+ for (print_counter = 80; print_counter > 0; print_counter--)
+ grub_printf("%s", buffer);
+}
GRUB_MOD_LICENSE ("GPLv3+");
@@ -506,8 +534,10 @@ GRUB_MOD_INIT(normal)
grub_script_init ();
grub_menu_init ();
+ printf_test('0');
grub_xputs_saved = grub_xputs;
grub_xputs = grub_xputs_normal;
+ printf_test('1');
/* Normal mode shouldn't be unloaded. */
if (mod)
--
2.11.0
_______________________________________________
Bug-grub mailing list
Bug-grub@gnu.org
https://lists.gnu.org/mailman/listinfo/bug-grub
