Re: [PATCH V2]networking: Allow dot at the end of the domain name in dhcp response

[Denys Vlasenko]

Applied, thanks

On Thu, Feb 11, 2016 at 6:24 AM, Rich Felker  wrote:
> On Thu, Feb 11, 2016 at 05:59:39AM +0100, Denys Vlasenko wrote:
>> On Tue, Feb 9, 2016 at 6:23 PM, Balaji Punnuru  
>> wrote:
>> > When a dhcp server responds with a domain name that ends with a ".",
>> > domain name validation is failing which leads to populating domain bad in
>> > resolv.conf
>> >
>> > Domain name ending with . is a valid syntax according RFC-1034.
>> >
>> > The Patch fixes the domain name validation which ends with "."
>>
>> Well, this may be technically allowed, but wouldn't you think that
>> such DHCP response is definitely odd, and it's better to know about it?
>
> Maybe a log message for the oddity, but it should not result in active
> misconfiguration. Ending dns names with a dot is valid and IIRC
> historically this practice was used to indicate that the name is
> anchored to the dns root rather than possibly being interpreted
> relative to some domain. The standard APIs for lookups all accept
> names ending with a dot, and this should suppress search domains.
>
> Rich
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Re: [PATCH V2]networking: Allow dot at the end of the domain name in dhcp response

[Denys Vlasenko]

On Tue, Feb 9, 2016 at 6:23 PM, Balaji Punnuru  wrote:
> When a dhcp server responds with a domain name that ends with a ".",
> domain name validation is failing which leads to populating domain bad in
> resolv.conf
>
> Domain name ending with . is a valid syntax according RFC-1034.
>
> The Patch fixes the domain name validation which ends with "."

Well, this may be technically allowed, but wouldn't you think that
such DHCP response is definitely odd, and it's better to know about it?

What DHCP server gave you such domain name? And why does it do that?
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Re: [PATCH V2]networking: Allow dot at the end of the domain name in dhcp response

[Rich Felker]

On Thu, Feb 11, 2016 at 05:59:39AM +0100, Denys Vlasenko wrote:
> On Tue, Feb 9, 2016 at 6:23 PM, Balaji Punnuru  
> wrote:
> > When a dhcp server responds with a domain name that ends with a ".",
> > domain name validation is failing which leads to populating domain bad in
> > resolv.conf
> >
> > Domain name ending with . is a valid syntax according RFC-1034.
> >
> > The Patch fixes the domain name validation which ends with "."
> 
> Well, this may be technically allowed, but wouldn't you think that
> such DHCP response is definitely odd, and it's better to know about it?

Maybe a log message for the oddity, but it should not result in active
misconfiguration. Ending dns names with a dot is valid and IIRC
historically this practice was used to indicate that the name is
anchored to the dns root rather than possibly being interpreted
relative to some domain. The standard APIs for lookups all accept
names ending with a dot, and this should suppress search domains.

Rich
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[PATCH V2]networking: Allow dot at the end of the domain name in dhcp response

[Balaji Punnuru]

When a dhcp server responds with a domain name that ends with a ".",
domain name validation is failing which leads to populating domain bad in
resolv.conf

Domain name ending with . is a valid syntax according RFC-1034.

The Patch fixes the domain name validation which ends with "."
The test results are as follows:

1. if DNS server returns with domain name "foo.test.com." , resolv.conf
gets populated with "domain foo.test.com."

2. if DNS server returns with domain name "foo.test.com" , resolv.conf gets
populated with "domain foo.test.com"

Without this Patch:
1. if DNS server returns with domain name "foo.test.com." , resolv.conf
gets populated with "domain bad "

2. if DNS server returns with domain name "foo.test.com" , resolv.conf gets
populated with "domain foo.test.com"


Details: In Some instances where DNS Servers sends out domain name
 in answer with a terminating ".", the validation logic for
 domain name is returning as bad domain.

 According to RFC 1034 Section 3.1, a character string
 which represents a complete domain name(often called "absolute").
 For example, "poneria.ISI.EDU."

 The fix done is to add a check for end of string after
 processing node which allows for presence of "." at the end of the
string

Signed-off-by: Balaji Punnuru 
---
 networking/udhcp/dhcpc.c | 12 
 1 file changed, 12 insertions(+)

diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 915f659..3d5b245 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -201,6 +201,18 @@ static int good_hostname(const char *name)
 //Do we want this?
 //return ((name - start) < 1025); /* NS_MAXDNAME */
 name++;
+/*
+   According to RFC 1034, section 3.1, trailing dots is
allowed,
+
+   Quoting from RFC 1034:
+   --
+   The most common interpretation uses the root "." as
either the
+   single origin or as one of the members of the search
list, so
+   a multi-label relative name is often one where the
trailing dot
+   has been omitted to save typing.
+*/
+if (*name == '\0')
+return 1;
 }
 }
 #else
-- 
2.1.4
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