Mailing List Archive: OpenSSH: Bugs

[Bug 1964] QoS/DSCP names false translated to ToS hex value

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bugzilla-daemon at bugzilla

Feb 23, 2012, 4:21 PM

Post #1 of 9 (379 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #1 from Damien Miller <djm [at] mindrot> 2012-02-24 11:21:26 EST ---
Created attachment 2132
--> https://bugzilla.mindrot.org/attachment.cgi?id=2132
ipqos-shift.diff

shift DSCP values 2 bits right to accommodate ECN flags

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bugzilla-daemon at bugzilla

Feb 23, 2012, 4:22 PM

Post #2 of 9 (365 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

Damien Miller <djm [at] mindrot> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |djm [at] mindrot,
| |philipp [at] redfish-solutions
| |om

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bugzilla-daemon at bugzilla

Feb 23, 2012, 8:59 PM

Post #3 of 9 (366 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #2 from Philip Prindeville <philipp [at] redfish-solutions> 2012-02-24 15:59:03 EST ---
(In reply to comment #1)
> Created attachment 2132 [details]
> ipqos-shift.diff
>
> shift DSCP values 2 bits right to accommodate ECN flags

The values *ARE* normalized to the TOS field being octet-aligned.

There is no shifting required.

Quoting RFC-2597:

6. Recommended Codepoints

Recommended codepoints for the four general use AF classes are given
below. These codepoints do not overlap with any other general use
PHB
groups.

The RECOMMENDED values of the AF codepoints are as follows: AF11 = '
001010', AF12 = '001100', AF13 = '001110', AF21 = '010010', AF22 = '
010100', AF23 = '010110', AF31 = '011010', AF32 = '011100', AF33 = '
011110', AF41 = '100010', AF42 = '100100', and AF43 = '100110'. The
table below summarizes the recommended AF codepoint values.

We take AF11 || 00 (i.e. shifted left 2 bits) and we get 0010100.00
which is 0x48.

Grepping through the sources, we get:

defines.h:65:# define IPTOS_DSCP_AF21 0x48

Likewise, quoting RFC-2474, Section 2:

Class Selector Codepoint: any of the eight codepoints in the range '
xxx000' (where 'x' may equal '0' or '1'). Class Selector Codepoints
are discussed in Sec. 4.2.2.

so CS1 would be 001000.00 or 0x20, indeed grepping through the source,
we get:

defines.h:78:# define IPTOS_CLASS_CS1 0x20

Again, THE VALUES DON'T REQUIRE A SHIFT.

There is no bug!

Please close this out as NOTABUG.

In the future, please check glibc's /usr/include/netinet/ip.h:

#define IPTOS_CLASS_MASK 0xe0
#define IPTOS_CLASS(class) ((class) & IPTOS_CLASS_MASK)
#define IPTOS_CLASS_CS0 0x00
#define IPTOS_CLASS_CS1 0x20

the value for the macro "class" is meant to be iph->ip_tos, which
represents all 8 bits of the TOS octet, including the ECN bits.

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bugzilla-daemon at bugzilla

Feb 23, 2012, 9:02 PM

Post #4 of 9 (361 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #3 from Philip Prindeville <philipp [at] redfish-solutions> 2012-02-24 16:02:41 EST ---
Sigh. Typo.

That should have read:

We take AF21 || 00 (i.e. shifted left 2 bits) and we get 010010.00
which is 0x48.

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bugzilla-daemon at bugzilla

Feb 23, 2012, 11:17 PM

Post #5 of 9 (365 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #4 from martin f. krafft <bugzilla.mindrot.org [at] pobox> 2012-02-24 18:17:26 EST ---
So it looks as if your #defines do not actually specify the hex value
of the DSCP classes, but they define the hex value shifted left by two
bits. For instance, cs1 is 0x08 in the RFC, but you store 0x20, which
is <<2.

This is all good and well and an implementation detail, really, but I
think the problem is that when someone specifies IPQoS=0x08, they
expect the same behaviour as if they specfied "cs1". However, 0x08 is
used directly without shifting, and so OpenSSH interprets it as 0x02,
which is undefined.

What is the reason that #defines specify shifted values instead of the
standard values, making the shift happen explicitly later?

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bugzilla-daemon at bugzilla

Feb 24, 2012, 6:55 PM

Post #6 of 9 (368 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #5 from Philip Prindeville <philipp [at] redfish-solutions> 2012-02-25 13:55:06 EST ---
(In reply to comment #4)
> So it looks as if your #defines do not actually specify the hex value
> of the DSCP classes, but they define the hex value shifted left by two
> bits. For instance, cs1 is 0x08 in the RFC, but you store 0x20, which
> is <<2.

They follow the notation that's present in /usr/include/netinet/ip.h
which has been present for 20 years. It's a POSIX standard.

> This is all good and well and an implementation detail, really, but I
> think the problem is that when someone specifies IPQoS=0x08, they
> expect the same behaviour as if they specfied "cs1". However, 0x08 is
> used directly without shifting, and so OpenSSH interprets it as 0x02,
> which is undefined.

Well, hopefully that person is acquainted with the BSD Sockets source
code and it will all look very familiar to him.

> What is the reason that #defines specify shifted values instead of the
> standard values, making the shift happen explicitly later?

Precedent and compatibility with existing source.

If you look at "defines.h", it says:

#include <netinet/ip.h>
...

#ifndef IPTOS_DSCP_AF11

i.e. it can get the definition from netinet/ip.h (and it's recent
enough to contain my patches to glibc 2.12). If those definitions
aren't present, then it #define's then to duplicate names and values.

The openssh sources don't do anything that isn't exactly the same as
what's done in FreeBSD, Linux, QNX, HP-UX, Solaris, etc.

I'm really not sure what the issue is here, other than we're trying too
hard to be compatible.

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bugzilla-daemon at bugzilla

Feb 24, 2012, 11:04 PM

Post #7 of 9 (373 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #6 from martin f. krafft <bugzilla.mindrot.org [at] pobox> 2012-02-25 18:04:55 EST ---
Your argument is comprehensible.

I don't know anything about the implementation details and would not
want to questions its correctness.

I am just a user, and I noticed that a call like

ssh -4o IPQoS=0x10 -S none lotus

yields (according to `tshark`:

0001 00.. = Differentiated Services Codepoint: Unknown (0x04)

which is wrong. <<2 would make this right.

Maybe this is related to #1963 or #1965.

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bugzilla-daemon at bugzilla

Feb 27, 2012, 11:30 PM

Post #8 of 9 (348 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #7 from Philip Prindeville <philipp [at] redfish-solutions> 2012-02-28 18:30:12 EST ---
Have you been able to reproduce this code that's been patched with the
fix in bug 1963?

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bugzilla-daemon at bugzilla

Feb 27, 2012, 11:39 PM

Post #9 of 9 (348 views)
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[Bug 1964] QoS/DSCP names false translated to ToS hex value [In reply to]

https://bugzilla.mindrot.org/show_bug.cgi?id=1964

--- Comment #8 from Philip Prindeville <philipp [at] redfish-solutions> 2012-02-28 18:39:38 EST ---
(In reply to comment #6)
> Your argument is comprehensible.
>
> I don't know anything about the implementation details and would not
> want to questions its correctness.
>
> I am just a user, and I noticed that a call like
>
> ssh -4o IPQoS=0x10 -S none lotus
>
> yields (according to `tshark`:
>
> 0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
>
> which is wrong. <<2 would make this right.
>
> Maybe this is related to #1963 or #1965.

For that matter, what happens when you run:

ssh -4o IPQoS=0x08 -S none lotus

Do you also see 0x04?

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