Hello,

Hi,

basically this patch works. But I have a few issues I would like to point out and use as a bit of an exercise for everyone.

On Sat, 2018-01-20 at 16:25 +0100, Peter Müller wrote:

...

DNSSEC-validating nameservers return an "ad" (Authenticated Data) flag in the DNS response header. This can be used as a negative indicator for DNSSEC validation: In case a nameserver does not return the flag, but failes to look up a domain with an invalid signature, it does not support DNSSEC validation.

This makes it easier to detect nameservers which do not fully comply to the RFCs or try to tamper DNS queries.

See bug #11595 (https://bugzilla.ipfire.org/show_bug.cgi?id=11595) for further details.

Signed-off-by: Peter Müller peter.mueller@link38.eu

src/initscripts/system/unbound | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/initscripts/system/unbound b/src/initscripts/system/unbound index 4e7e63e5f..410631f86 100644 --- a/src/initscripts/system/unbound +++ b/src/initscripts/system/unbound @@ -364,7 +364,12 @@ ns_is_validating() { local ns=${1} shift

• dig @${ns} A ${TEST_DOMAIN_FAIL} $@ | grep -q SERVFAIL

• if ! dig @${ns} A ${TEST_DOMAIN_FAIL} $@ | grep -q SERVFAIL; then

• return 1
  

• else

• # Determine if NS replies with "ad" data flag if DNSSEC
  

enabled

• dig @${ns} +dnssec SOA ${TEST_DOMAIN} $@ | grep "\;\;\
  

flags:" | awk -F: '{ print $2 }' | awk -F; '{ print $1 }' | grep -q "\ ad"

• fi

a) Parsing the human-readable output of a tool is always a bad idea. It might change or change just one character and the entire chain doesn't work any more. Let's hope we will notice that before our users do.

You are right. There seems to be no way how to just get the answer flags out of dig, all we can do is suppressing some data parts unused here:

dig SOA +dnssec +adflag +noanswer +noquestion +nostats ipfire.org

This does not fully solve the problem, but reduces the chance that some clutter in the actual answer data section might cause false-positives.

b) There is no need to use grep here. awk can grep like this:

awk /;; flags:/ -F: '{ print $2 }'

Thank you, I will send in a second patch.

That will save you from calling grep here which increases performance. Using awk and grep is also not really a good idea because every subprocess takes ages to execute.

Agreed.

The network code in IPFire 3 doesn't use awk at all and grep in rare cases.

https://git.ipfire.org/?p=network.git&a=search&h=HEAD&st=grep&am... https://git.ipfire.org/?p=network.git&a=search&h=HEAD&st=grep&am...

Wow! I use them virtually everywhere... :-)

Best regards, Peter Müller

But to not complicate the code too much we can use awk here. But there is no need for grep.

...

}

# Checks if we can retrieve the DNSKEY for this domain.

Best, -Michael