Messages in this thread | | | Date | Mon, 26 Jan 2004 11:49:52 +0100 | From | goblin@ajt ... | Subject | Bug in virtual console scrollback buffer? |
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1. I think I found a bug in linux' 2.6.1 vt scrollback buffer
2. I've noticed some changes in linux 2.6.1 scrollback buffer. I'm not sure, but I once noticed that Shift-PgUp worked even after switching a console (Alt-F?). Few days later I wanted to check this out and test it again. Well, it didn't work. But I noticed a wierd thing:
After switching the console you are normally unable to see the scrollback buffer. But when program "screen" is run, you may view it's internal console scrollback buffer using ^A,^[ (and pg-ups). It's nothing unusual in this, but when you leave the copy mode (eg. with Esc) and use kernel's internal Shift-PgUp, you are able to see the scrollback buffers of previously used virtual consoles. I think this may even be a security violation as you can see what root typed on his console and sometimes even recent dmesg messages. More to this, sometimes text in scrolled back buffers is shifted to the right about 16 chars (when you toy with Shift-PgUp/PgDn you notice it's sometimes normal, sometimes shifted).
I'm not sure whether or not this behavior is intended, but it seems a bug for me. Well, I wasn't able to get any oops, thrash on screen, segfault or any error like that, the kernel remained stable all the time.
3. (keywords:) screen, vt, scrollback
4. kernel version: Linux version 2.6.1 (goblin@goblin) (gcc version 3.2.3) #2 Wed Jan 21 08:42:57 CET 2004
5. No oops message or any kernel destabilization
6. To trigger the problem, use the program screen and it's scrollback buffer with Ctrl-A, Ctrl-[.
7. Environment: 7.1 software Screen version 3.09.15 (FAU) 13-Mar-03
sh ver_linux: Linux goblin 2.6.1 #2 Wed Jan 21 08:42:57 CET 2004 i686 unknown unknown GNU/Linux
Gnu C 3.2.3 Gnu make 3.80 util-linux 2.12 mount 2.12 module-init-tools 0.9.14 e2fsprogs 1.34 jfsutils 1.1.3 xfsprogs 2.5.6 pcmcia-cs 3.2.5 PPP 2.4.1 nfs-utils 1.0.6 Linux C Library 2.3.2 Dynamic linker (ldd) 2.3.2 Linux C++ Library 5.0.3 Procps 2.0.16 Net-tools 1.60 Kbd 1.08 Sh-utils 5.0 (No loaded modules) Kernel is compiled with framebuffer console as a module, but this module isn't in use (and wasn't since boot). I use only text-mode console for this, I haven't tested this bug with framebuffer device yet.
7.2 processor: goblin@goblin:/usr/src/linux/scripts$ cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 5 model name : Pentium II (Deschutes) // it's actually a Celeron stepping : 1 cpu MHz : 300.821 cache size : 32 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 2 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr bogomips : 591.87
7.3 no modules loaded
7.4 and the rest: Well, I have a 2mb-s3 virge(pci) and temporarily 32mb-s3 savage (agp), but this shouldn't be relevant as the bug occurs in text mode.
By the way, why in 2.6 I've 8 Bogomips less than in 2.4? ;-)
If possible, I'd like to hear from you about this bug Thank you and may the penguins be with you :-)
-- Goblin Robert Goliasz goblin@ajt.k5.pl or rgoliasz@poczta.onet.pl - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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