[bug #56654] Bug in grub_xputs_normal

[Stephan]

URL:
  <https://savannah.gnu.org/bugs/?56654>

                 Summary: Bug in grub_xputs_normal
                 Project: GNU GRUB
            Submitted by: sgabert
            Submitted on: Mon 22 Jul 2019 06:26:14 AM UTC
                Category: None
                Severity: Major
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 
                 Release: Git master
         Reproducibility: Every Time
         Planned Release: None

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Details:

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.


(originally sent to bug-grub:
https://lists.gnu.org/archive/html/bug-grub/2019-07/msg00015.html)



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File Attachments:


-------------------------------------------------------
Date: Mon 22 Jul 2019 06:26:14 AM UTC  Name: bug-xputs.patch  Size: 2KiB   By:
sgabert
A small patch that triggers the bug.
<http://savannah.gnu.org/bugs/download.php?file_id=47245>

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