two 2.5 modules bugs

two 2.5 modules bugs

[Mikael Pettersson]

1. With kernel 2.5.53 and module-init-tools-0.9.6, "modprobe tulip"
   fails and goes into an infinite CPU-consuming loop. The problem
   appears to be related to the dependency from tulip to crc32. If I
   manually modprobe crc32 before modprobe tulip, it works. If crc32
   isn't loaded, modprobe tulip first loads crc32 and then loops.

   module-init-tools-0.9.5 did not have this problem.

2. The implementation of old-style MODULE_PARMs with type "1-16s"
   is broken. Instead of splicing the parameter at the commas and
   storing pointers to the substrings in consecutive array elements,
   the whole string is stored in the array instead.

   Consider parport_pc.c, which contains (simplified):

   static const char *irq[16];
   MODULE_PARM(irq, "1-16s");

   "modprobe parport_pc irq=007" should store a pointer to "007" in
   irq[0], but instead (unsigned int)irq[0] == 0x00373030, the ASCII
   representation of "007" in little-endian. (Kernel 2.5.53 on x86,
   with module-init-tools-0.9.[56].)

/Mikael

Re: two 2.5 modules bugs

[Petr Vandrovec]

On Fri, Dec 27, 2002 at 05:16:35PM +0100, Mikael Pettersson wrote:
> 1. With kernel 2.5.53 and module-init-tools-0.9.6, "modprobe tulip"
>    fails and goes into an infinite CPU-consuming loop. The problem
>    appears to be related to the dependency from tulip to crc32. If I
>    manually modprobe crc32 before modprobe tulip, it works. If crc32
>    isn't loaded, modprobe tulip first loads crc32 and then loops.
> 
>    module-init-tools-0.9.5 did not have this problem.

Load modprobe with MALLOC_CHECK_=1. It will reveal that it tries to
free() some non-mallocated area. 

Try patch below, insmod() can realloc/free its second argument, so
we can doublefree it, and glibc's malloc goes wild. It fixes problems
I had with modprobe ipx (which depends on psnap/p8022 which depends
on llc).
 
--- 0.9.6-1/modprobe.c.dist	2002-12-26 10:32:22.000000000 +0100
+++ 0.9.6-1/modprobe.c	2002-12-28 00:12:16.000000000 +0100
@@ -582,7 +582,7 @@
 		char *baseopts = NOFAIL(strdup(""));
 		insmod(list, baseopts, NULL, 0, dry_run, verbose, options,
 		       commands, 0);
-		free(baseopts);
+//		free(baseopts);
 	}
 
 	/* Did config file override command or add options? */

							Petr Vandrovec
							vandrove@vc.cvut.cz

Re: two 2.5 modules bugs

[Rusty Russell]

In message <200212271616.RAA03356@harpo.it.uu.se> you write:
> 1. With kernel 2.5.53 and module-init-tools-0.9.6, "modprobe tulip"
>    fails and goes into an infinite CPU-consuming loop. The problem
>    appears to be related to the dependency from tulip to crc32. If I
>    manually modprobe crc32 before modprobe tulip, it works. If crc32
>    isn't loaded, modprobe tulip first loads crc32 and then loops.
> 
>    module-init-tools-0.9.5 did not have this problem.

This should be fixed in 0.9.6: a double free caused all kinds of wierd
behavior.  Please tell me if this fixes it.

> 2. The implementation of old-style MODULE_PARMs with type "1-16s"
>    is broken. Instead of splicing the parameter at the commas and
>    storing pointers to the substrings in consecutive array elements,
>    the whole string is stored in the array instead.
> 
>    Consider parport_pc.c, which contains (simplified):
> 
>    static const char *irq[16];
>    MODULE_PARM(irq, "1-16s");
> 
>    "modprobe parport_pc irq=007" should store a pointer to "007" in
>    irq[0], but instead (unsigned int)irq[0] == 0x00373030, the ASCII
>    representation of "007" in little-endian. (Kernel 2.5.53 on x86,
>    with module-init-tools-0.9.[56].)

Ew.  I horribly misinterpreted "1-16s" to mean "a string 1-16 chars
long".  The obvious fix (untested) is:

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.53/kernel/module.c working-2.5.53-sparam/kernel/module.c
--- linux-2.5.53/kernel/module.c	2002-12-26 15:41:06.000000000 +1100
+++ working-2.5.53-sparam/kernel/module.c	2002-12-28 21:32:34.000000000 +1100
@@ -604,7 +604,8 @@ extern int set_obsolete(const char *val,
 		return param_array(kp->name, val, min, max, obsparm->addr,
 				   sizeof(long), param_set_long);
 	case 's':
-		return param_string(kp->name, val, min, max, obsparm->addr);
+		return param_array(kp->name, val, min, max, obsparm->addr,
+				   sizeof(char *), param_set_charp);
 	}
 	printk(KERN_ERR "Unknown obsolete parameter type %s\n", obsparm->type);
 	return -EINVAL;

I'll test this tomorrow...

Thanks for the bug report!
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Want a random entropy source?

[Stephen Satchell]

Not too long ago I had made a submission on SlashDot on something-or-other 
(oh, right, "Rube-Goldberg Type Random Number Generators?" 
http://ask.slashdot.org/article.pl?sid=02/07/26/1751228&tid=137) and I 
stumbled across my submission to that article.  After thinking about it, I 
though it might be a reasonable thing to submit to this list as a possible 
enhancement to the /dev/random driver if someone wants to try it.  My 
submission was thus:

"I've been vexed that the sound card plus CD-ROM drive combination always 
shows signal at around -50 dBVU in CoolEdit. So, just for grins, I decided 
to capture a few seconds of the noise and analyze the properties. I was 
astonished to see that the resulting signal is a white-noise pattern with a 
slight emphasis at the high end (when sampled at 44 kilosamples per 
second). In short, it looks like diode noise with a 4 kilohertz square wave 
thrown in.

"That suggests to me that this would make a fair source of random samples, 
especially after you slot out the interfering signal.

"How many computers don't have cheap sound cards and CD-ROM drives?"

For what it's worth...

Satch

Re: Want a random entropy source?

[John Bradford]

> I was astonished to see that the resulting signal is a white-noise
> pattern with a slight emphasis at the high end (when sampled at 44
> kilosamples per second). In short, it looks like diode noise with a
> 4 kilohertz square wave thrown in.

> "That suggests to me that this would make a fair source of random samples, 
> especially after you slot out the interfering signal.

How can you guarantee that you are sampling noise, though, what if a
sound card was picking up 50 Hz mains hum, for example,  that would
de-randomise the data quite a bit.

> "How many computers don't have cheap sound cards and CD-ROM drives?"

I have never understood how a 16-bit DAC or ADC can have noise above
96 dB.  Surely _by definition_ a 16-bit DAC or ADC is one that does
not have noise above that level.

John.

Re: Want a random entropy source?

[Dr. David Alan Gilbert]

* John Bradford (john@grabjohn.com) wrote:
> 
> I have never understood how a 16-bit DAC or ADC can have noise above
> 96 dB.  Surely _by definition_ a 16-bit DAC or ADC is one that does
> not have noise above that level.

Simple; the ADC might (ha - if you are lucky) have a nice low noise
figure; but its on a cheap sound card in a PC with god knows how much
other mush, with a cheap PSU with a piece of string connecting it to the 
CDROM and loads of other crap.

Dave
 ---------------- Have a happy GNU millennium! ----------------------   
/ Dr. David Alan Gilbert    | Running GNU/Linux on Alpha,68K| Happy  \ 
\ gro.gilbert @ treblig.org | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/

Re: Want a random entropy source?

[Russell King]

On Sat, Dec 28, 2002 at 04:00:25PM +0000, John Bradford wrote:
> I have never understood how a 16-bit DAC or ADC can have noise above
> 96 dB.  Surely _by definition_ a 16-bit DAC or ADC is one that does
> not have noise above that level.

You're assuming that the ADC input is coupled to a noiseless source.
Most ADCs have a chunk of analogue circuitry just before them which
is a nice source of noise.

Not only will noise be picked up via disconnected inputs, but it will
also be picked up via the power supply and ground connections to that
analogue circuit.  How much of that noise gets into the ADC input is
dependent on the quality, design and physical layout of the analogue
circuit.

(As a side note, it's interesting that (what used to be) Crystal
Semiconductor published a large chunk of information on the layout of
boards including the routing of power supplies for combined digital
and analogue circuits (and ADCs fall into that category.))

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

Re: Want a random entropy source?

[John Bradford]

> > I have never understood how a 16-bit DAC or ADC can have noise above
> > 96 dB.  Surely _by definition_ a 16-bit DAC or ADC is one that does
> > not have noise above that level.
> 
> You're assuming that the ADC input is coupled to a noiseless source.
> Most ADCs have a chunk of analogue circuitry just before them which
> is a nice source of noise.
> 
> Not only will noise be picked up via disconnected inputs, but it will
> also be picked up via the power supply and ground connections to that
> analogue circuit.  How much of that noise gets into the ADC input is
> dependent on the quality, design and physical layout of the analogue
> circuit.

Right...  So basically it can be claimed to be a 16-bit ADC as long as
it is noiseless above 96 dB, when all of the inputs to the ADC are
correctly terminated directly at the ADC inputs.

I just think it's funny that loads of "16-bit" soundcards are
effectively only 12-bit soundcards :-).  Especially as that's about
the noise-floor of good quality vinyl :-).

> (As a side note, it's interesting that (what used to be) Crystal
> Semiconductor published a large chunk of information on the layout of
> boards including the routing of power supplies for combined digital
> and analogue circuits (and ADCs fall into that category.))

Good idea - I'd be grateful if more manufacturers would supply a
datasheet at all :-).

John.

RE: Want a random entropy source?

[Folkert van Heusden]

> I was astonished to see that the resulting signal is a white-noise
> pattern with a slight emphasis at the high end (when sampled at 44
> kilosamples per second). In short, it looks like diode noise with a
> 4 kilohertz square wave thrown in.
> "That suggests to me that this would make a fair source of random samples,
> especially after you slot out the interfering signal.
JB> How can you guarantee that you are sampling noise, though, what if a
JB> sound card was picking up 50 Hz mains hum, for example,  that would
JB> de-randomise the data quite a bit.

Well, the 50hz from the mains isn't a perfect 50hz; it has random (yes)
fluctuations.

Re: Want a random entropy source?

[John Bradford]

> > I was astonished to see that the resulting signal is a white-noise
> > pattern with a slight emphasis at the high end (when sampled at 44
> > kilosamples per second). In short, it looks like diode noise with a
> > 4 kilohertz square wave thrown in.
> > "That suggests to me that this would make a fair source of random samples,
> > especially after you slot out the interfering signal.
> JB> How can you guarantee that you are sampling noise, though, what if a
> JB> sound card was picking up 50 Hz mains hum, for example,  that would
> JB> de-randomise the data quite a bit.
> 
> Well, the 50hz from the mains isn't a perfect 50hz; it has random (yes)
> fluctuations.

Yes, that's true.

More generally, though, is there any point in this going in to the
mainline kernel, if:

* Most users don't need faster entropy generation than we've got

and

* The entropy gathered from the soundcard is statistically inferior to
that gathered from the current sources of entropy.

I don't see how it's possible to guarantee that the data below a
certain dB level from the soundcard is noise.

John.

RE: Want a random entropy source?

[Folkert van Heusden]

> Well, the 50hz from the mains isn't a perfect 50hz; it has random (yes)
> fluctuations.
JB> Yes, that's true.
JB> More generally, though, is there any point in this going in to the
JB> mainline kernel, if:
JB> * Most users don't need faster entropy generation than we've got
JB> and
JB> * The entropy gathered from the soundcard is statistically inferior to
JB> that gathered from the current sources of entropy.

Well, there isn't any :o) That's why there's a user-level implementation
for such a beast for those who do need it.
( http://www.vanheusden.com/mirrors/audio-entropyd-0.0.5.tgz )

JB> I don't see how it's possible to guarantee that the data below a
JB> certain dB level from the soundcard is noise.

Some guy contacted me about audio-entropyd and told me he'd done a lot
of analysis on all how this and gave me a few hints how to improve the
quality of what is produced with this tool. A quick fourier-
transformation doesn't really show any peaks.

RE: Want a random entropy source?

[Stephen Satchell]

At 09:28 PM 12/28/02 +0100, Folkert van Heusden wrote:
>JB> How can you guarantee that you are sampling noise, though, what if a
>JB> sound card was picking up 50 Hz mains hum, for example,  that would
>JB> de-randomise the data quite a bit.
>
>Well, the 50hz from the mains isn't a perfect 50hz; it has random (yes)
>fluctuations.

As a start, I would slot out 50 Hz, 60 Hz (for people in the US and 
US-engineered power systems in other countries), 4 kHz and 
harmonics.  Actually, if you are sampling at roughly random intervals you 
would get about four to six bits per sample of somewhat random values, and 
that would give you entropy as good as you get from mouse movement.

If someone were playing a CD at the time you were sampling the sound card, 
you would get considerably more bits of entropy, but using the six bottom 
bits would still be useful.

Hey, people, it's just a thought.  Turning lemons into lemonade, if you will.

Satch

Re: Want a random entropy source?

[John Bradford]

> Hey, people, it's just a thought.  Turning lemons into lemonade, if you will.

Oh, I wasn't suggesting that it wasn't a useful idea, I was just
curious as to how random the entropy would be compared to other
sources such as disk and mouse activity.

John.

RE: Want a random entropy source?

[Folkert van Heusden]

Try this one: http://www.vanheusden.com/mirrors/audio-entropyd-0.0.5.tgz

(and if you have an unused video4linux-device, look here:
http://www.vanheusden.com/ved/ )

-----Oorspronkelijk bericht-----
Van: linux-kernel-owner@vger.kernel.org
[mailto:linux-kernel-owner@vger.kernel.org]Namens Stephen Satchell
Verzonden: zaterdag 28 december 2002 16:40
Aan: linux-kernel@vger.kernel.org
Onderwerp: Want a random entropy source?


Not too long ago I had made a submission on SlashDot on something-or-other
(oh, right, "Rube-Goldberg Type Random Number Generators?"
http://ask.slashdot.org/article.pl?sid=02/07/26/1751228&tid=137) and I
stumbled across my submission to that article.  After thinking about it, I
though it might be a reasonable thing to submit to this list as a possible
enhancement to the /dev/random driver if someone wants to try it.  My
submission was thus:

"I've been vexed that the sound card plus CD-ROM drive combination always
shows signal at around -50 dBVU in CoolEdit. So, just for grins, I decided
to capture a few seconds of the noise and analyze the properties. I was
astonished to see that the resulting signal is a white-noise pattern with a
slight emphasis at the high end (when sampled at 44 kilosamples per
second). In short, it looks like diode noise with a 4 kilohertz square wave
thrown in.

"That suggests to me that this would make a fair source of random samples,
especially after you slot out the interfering signal.

"How many computers don't have cheap sound cards and CD-ROM drives?"

For what it's worth...

Satch

-
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/