Hash results in non-distinct value when address and rdata are the same value

[rwstauner]

For a call to getresources(domain, "AAAA") i noticed all the items were resulting in the same .hash.

I'm not very familiar with this library, but i noticed that in that response the objects look like this:

 #<Dnsruby::RR::IN::AAAA:0x0000000103f1c490
  @address=#<Dnsruby::IPv6 ...>,
  @klass=IN,
  @name=#<Dnsruby::Name: ...>,
  @rdata=#<Dnsruby::IPv6 ...>,
  @ttl=223,
  @type=AAAA>

compared to just instantiating an object:

*irb /main:073:0:> Dnsruby::RR::IN::AAAA.new("::2")
 => #<Dnsruby::RR::IN::AAAA:0x0000000103e9ae18 @address=#<Dnsruby::IPv6 ::2>, @rdata="::2">

In the latter the rdata is a string and the address is an object. In the former, the rdata is also an object. Since it has the same value as the address object, the exclusive-or in the hash method results in zero:

*irb /main:077:0:> ["::1", "::2"].map { |addr| Dnsruby::IPv6.create(addr) }.map { |ip| Dnsruby::RR::IN::AAAA.new(ip) }.map { |x| {object: x, hash: x.hash} }
 =>
[{:object=>
   #<Dnsruby::RR::IN::AAAA:0x0000000103b385e0
    @address=#<Dnsruby::IPv6 ::1>,
    @rdata=#<Dnsruby::IPv6 ::1>>,
  :hash=>0},
 {:object=>
   #<Dnsruby::RR::IN::AAAA:0x0000000103b38590
    @address=#<Dnsruby::IPv6 ::2>,
    @rdata=#<Dnsruby::IPv6 ::2>>,
  :hash=>0}]

I'm not sure if rdata should be a string, or if the hash method should account for seen values, or one of those instance variables should be dropped from the calculation. Also not sure what other resource types may be affected.

[alexdalitz]

Maybe try :

RR::IN::AAAA.new.from_string("::1”);

?

On 13 Mar 2023, at 17:00, Randy Stauner @.***> wrote:

For a call to getresources(domain, "AAAA") i noticed all the items were resulting in the same .hash.

I'm not very familiar with this library, but i noticed that in that response the objects look like this:

<Dnsruby::RR::IN::AAAA:0x0000000103f1c490

@address=#<Dnsruby::IPv6 ...>, @klass=IN, @name=#<Dnsruby::Name: ...>, @rdata=#<Dnsruby::IPv6 ...>, @ttl=223, @type=AAAA> compared to just instantiating an object:

*irb /main:073:0:> Dnsruby::RR::IN::AAAA.new("::2") => #<Dnsruby::RR::IN::AAAA:0x0000000103e9ae18 @address=#, @rdata="::2"> In the latter the rdata is a string and the address is an object. In the former, the rdata is also an object. Since it has the same value as the address object, the exclusive-or in the hash method results in zero:

*irb /main:077:0:> ["::1", "::2"].map { |addr| Dnsruby::IPv6.create(addr) }.map { |ip| Dnsruby::RR::IN::AAAA.new(ip) }.map { |x| {object: x, hash: x.hash} } => [{:object=>

<Dnsruby::RR::IN::AAAA:0x0000000103b385e0

@address=#<Dnsruby::IPv6 ::1>,
@rdata=#<Dnsruby::IPv6 ::1>>,

:hash=>0}, {:object=>

<Dnsruby::RR::IN::AAAA:0x0000000103b38590

@address=#<Dnsruby::IPv6 ::2>,
@rdata=#<Dnsruby::IPv6 ::2>>,

:hash=>0}] I'm not sure if rdata should be a string, or if the hash method should account for seen values, or one of those instance variables should be dropped from the calculation. Also not sure what other resource types may be affected.

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[keithrbennett]

This worked for me:

Dnsruby::RR::IN::AAAA.new.from_string("::1");

Alex, your last double quote was some other fancy double quote character:

[10] pry(main)> "::1”".chars.last.bytes => [226, 128, 157]

• Keith

On Tue, Mar 14, 2023 at 1:41 AM Alex Dalitz @.***> wrote:

Maybe try :

RR::IN::AAAA.new.from_string("::1”);

?

On 13 Mar 2023, at 17:00, Randy Stauner @.***> wrote:

For a call to getresources(domain, "AAAA") i noticed all the items were resulting in the same .hash.

I'm not very familiar with this library, but i noticed that in that response the objects look like this:

<Dnsruby::RR::IN::AAAA:0x0000000103f1c490

@address=#<Dnsruby::IPv6 ...>, @klass=IN, @name=#<Dnsruby::Name: ...>, @rdata=#<Dnsruby::IPv6 ...>, @ttl=223, @type=AAAA> compared to just instantiating an object:

*irb /main:073:0:> Dnsruby::RR::IN::AAAA.new("::2") => #<Dnsruby::RR::IN::AAAA:0x0000000103e9ae18 @address=#<Dnsruby::IPv6 ::2>, @rdata="::2"> In the latter the rdata is a string and the address is an object. In the former, the rdata is also an object. Since it has the same value as the address object, the exclusive-or in the hash method results in zero:

*irb /main:077:0:> ["::1", "::2"].map { |addr| Dnsruby::IPv6.create(addr) }.map { |ip| Dnsruby::RR::IN::AAAA.new(ip) }.map { |x| {object: x, hash: x.hash} } => [{:object=>

<Dnsruby::RR::IN::AAAA:0x0000000103b385e0

@address=#, @rdata=#>, :hash=>0}, {:object=>

<Dnsruby::RR::IN::AAAA:0x0000000103b38590

@address=#, @rdata=#>, :hash=>0}] I'm not sure if rdata should be a string, or if the hash method should account for seen values, or one of those instance variables should be dropped from the calculation. Also not sure what other resource types may be affected.

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[rwstauner]

I'm sorry, I wasn't clear. I was attempting to help demonstrate how the bug with .hash seems to be occurring.

I'm not trying to manually construct these classes, I'm just using Dnsruby::DNS#getresources:

irb(main):006:0> Dnsruby::DNS.new.getresources("aaaa.test.r4s6.net", "AAAA").map { |
x| {object: x, hash: x.hash } }
=>
[{:object=>
   #<Dnsruby::RR::IN::AAAA:0x00007fd451ad05c0
    @address=#<Dnsruby::IPv6 ::1>,
    @klass=IN,
    @name=#<Dnsruby::Name: aaaa.test.r4s6.net.>,
    @rdata=#<Dnsruby::IPv6 ::1>,
    @ttl=20,
    @type=AAAA>,
  :hash=>1645861387863113502},
 {:object=>
   #<Dnsruby::RR::IN::AAAA:0x00007fd451ad0520
    @address=#<Dnsruby::IPv6 ::2>,
    @klass=IN,
    @name=#<Dnsruby::Name: aaaa.test.r4s6.net.>,
    @rdata=#<Dnsruby::IPv6 ::2>,
    @ttl=20,
    @type=AAAA>,
  :hash=>1645861387863113502}]

This call to getresources returns 2 different addresses that each produce the same .hash.

[alexdalitz]

I see - thanks!

It turns out that the way the RR hash is being calculated includes the @rdata, as well as the @address. However, in the AAAA record, they are the same thing, so this code :

def hash # :nodoc: vars = (self.instance_variables - @.***).sort vars.inject(0) do |hash_value, var_name| hash_value ^ self.instance_variable_get(var_name).hash end end ...actually negates the @rdata with the @address, leading to both these records having the same hash.

I will push a change which takes the @rdata out of the hash value, which gives you different hashes for these two records.

If you need this in a new gem, please let me know.

Thanks,

Alex.

On 14 Mar 2023, at 14:28, Randy Stauner @.***> wrote:

I'm sorry, I wasn't clear. I was attempting to help demonstrate how the bug with .hash seems to be occurring.

I'm not trying to manually construct these classes, I'm just using Dnsruby::DNS#getresources:

irb(main):006:0> Dnsruby::DNS.new.getresources("aaaa.test.r4s6.net", "AAAA").map { | x| {object: x, hash: x.hash } } => [{:object=>

<Dnsruby::RR::IN::AAAA:0x00007fd451ad05c0

@address=#<Dnsruby::IPv6 ::1>,
@klass=IN,
@name=#<Dnsruby::Name: aaaa.test.r4s6.net.>,
@rdata=#<Dnsruby::IPv6 ::1>,
@ttl=20,
@type=AAAA>,

:hash=>1645861387863113502}, {:object=>

<Dnsruby::RR::IN::AAAA:0x00007fd451ad0520

@address=#<Dnsruby::IPv6 ::2>,
@klass=IN,
@name=#<Dnsruby::Name: aaaa.test.r4s6.net.>,
@rdata=#<Dnsruby::IPv6 ::2>,
@ttl=20,
@type=AAAA>,

:hash=>1645861387863113502}] This call to getresources returns 2 different addresses that each produce the same .hash.

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[rwstauner]

i don't need it, just noticed the odd behavior. thanks!

[alexdalitz]

This is now fixed in the newly released v1.70.0 - thanks