resolver

package
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 Go to latest Published: Apr 15, 2020 License: AGPL-3.0 Imports: 24 Imported by: 0

Documentation

Overview

Package resolver is responsible for querying DNS.

DNS Servers

Internal lists of resolvers to use are built on start and rebuilt on every config or network change. Configured DNS servers are prioritized over servers assigned by dhcp. Domain and search options (here referred to as "search scopes") are being considered.

Security

Usage of DNS Servers can be regulated using the configuration: 

DoNotUseAssignedDNS        // Do not use DNS servers assigned by DHCP
DoNotUseMDNS               // Do not use mDNS
DoNotForwardSpecialDomains // Do not forward special domains to local resolvers, except if they have a search scope for it

Note: The DHCP options "domain" and "search" are ignored for servers assigned by DHCP that do not reside within local address space.

Resolving DNS

Various different queries require the resolver to behave in different manner:

Queries for "localhost." are immediately responded with 127.0.0.1 and ::1, for A and AAAA queries and NXDomain for others. Reverse lookups on local address ranges (10/8, 172.16/12, 192.168/16, fe80::/7) will be tried against every local resolver and finally mDNS until a successful, non-NXDomain answer is received. Special domains ("example.", "example.com.", "example.net.", "example.org.", "invalid.", "test.", "onion.") are resolved using search scopes and local resolvers. All other domains are resolved using search scopes and all available resolvers.

Index

Constants

View Source 
const (
	ServerTypeDNS = "dns"
	ServerTypeTCP = "tcp"
	ServerTypeDoT = "dot"
	ServerTypeDoH = "doh"

	ServerSourceConfigured = "config"
	ServerSourceAssigned   = "dhcp"
	ServerSourceMDNS       = "mdns"
)

DNS Resolver Attributes

View Source 
const (
	DNSClassMulticast = dns.ClassINET | 1<<15
)

DNS Classes

Variables

View Source 
var (
	CfgOptionNameServersKey = "dns/nameservers"

	CfgOptionNameserverRetryRateKey = "dns/nameserverRetryRate"

	CfgOptionNoMulticastDNSKey = "dns/noMulticastDNS"

	CfgOptionNoAssignedNameserversKey = "dns/noAssignedNameservers"

	CfgOptionNoInsecureProtocolsKey = "dns/noInsecureProtocols"

	CfgOptionDontResolveSpecialDomainsKey = "dns/dontResolveSpecialDomains"

	CfgOptionDontResolveTestDomainsKey = "dns/dontResolveTestDomains"
)

Configuration Keys

View Source 
var (

	// ErrNotFound is a basic error that will match all "not found" errors
	ErrNotFound = errors.New("record does not exist")
	// ErrBlocked is basic error that will match all "blocked" errors
	ErrBlocked = errors.New("query was blocked")
	// ErrLocalhost is returned to *.localhost queries
	ErrLocalhost = errors.New("query for localhost")

	// ErrTestDomainsDisabled wraps ErrBlocked
	ErrTestDomainsDisabled = fmt.Errorf("%w: test domains disabled", ErrBlocked)
	// ErrSpecialDomainsDisabled wraps ErrBlocked
	ErrSpecialDomainsDisabled = fmt.Errorf("%w: special domains disabled", ErrBlocked)
	// ErrInvalid wraps ErrNotFound
	ErrInvalid = fmt.Errorf("%w: invalid request", ErrNotFound)
	// ErrNoCompliance wraps ErrBlocked and is returned when no resolvers were able to comply with the current settings
	ErrNoCompliance = fmt.Errorf("%w: no compliant resolvers for this query", ErrBlocked)
)

Functions

func ResolveIPAndValidate 

func ResolveIPAndValidate(ctx context.Context, ip string, securityLevel uint8) (domain string, err error)

ResolveIPAndValidate finds (reverse DNS), validates (forward DNS) and returns the domain name assigned to the given IP.

func SetLocalAddrFactory 

func SetLocalAddrFactory(laf func(network string) net.Addr)

SetLocalAddrFactory supplies the intel package with a function to get permitted local addresses for connections.

Types

type BasicResolverConn 

type BasicResolverConn struct {
	sync.Mutex // for lastFail
	// contains filtered or unexported fields
}

BasicResolverConn implements ResolverConn for standard dns clients.

func (*BasicResolverConn) LastFail 

func (brc *BasicResolverConn) LastFail() time.Time

LastFail returns the internal lastfail value while locking the Resolver.

func (*BasicResolverConn) MarkFailed 

func (brc *BasicResolverConn) MarkFailed()

MarkFailed marks the resolver as failed.

func (*BasicResolverConn) Query 

func (brc *BasicResolverConn) Query(ctx context.Context, q *Query) (*RRCache, error)

Query executes the given query against the resolver.

type IPInfo 

type IPInfo struct {
	record.Base
	sync.Mutex

	IP      string
	Domains []string
}

IPInfo represents various information about an IP.

func GetIPInfo 

func GetIPInfo(ip string) (*IPInfo, error)

GetIPInfo gets an IPInfo record from the database.

func (*IPInfo) AddDomain 

func (ipi *IPInfo) AddDomain(domain string) (added bool)

AddDomain adds a domain to the list and reports back if it was added, or was already present.

func (*IPInfo) FmtDomains 

func (ipi *IPInfo) FmtDomains() string

FmtDomains returns a string consisting of the domains that have seen to use this IP, joined by " or "

func (*IPInfo) Save 

func (ipi *IPInfo) Save() error

Save saves the IPInfo record to the database.

func (*IPInfo) String 

func (ipi *IPInfo) String() string

FmtDomains returns a string consisting of the domains that have seen to use this IP, joined by " or "

type NameRecord 

type NameRecord struct {
	record.Base
	sync.Mutex

	Domain   string
	Question string
	Answer   []string
	Ns       []string
	Extra    []string
	TTL      int64

	Server      string
	ServerScope int8
}

NameRecord is helper struct to RRCache to better save data to the database.

func GetNameRecord 

func GetNameRecord(domain string, question string) (*NameRecord, error)

GetNameRecord gets a NameRecord from the database.

func (*NameRecord) Save 

func (rec *NameRecord) Save() error

Save saves the NameRecord to the database.

type Query 

type Query struct {
	FQDN               string
	QType              dns.Type
	SecurityLevel      uint8
	NoCaching          bool
	IgnoreFailing      bool
	LocalResolversOnly bool
	// contains filtered or unexported fields
}

Query describes a dns query.

type RRCache 

type RRCache struct {
	sync.Mutex

	Domain   string   // constant
	Question dns.Type // constant

	Answer []dns.RR // might be mixed
	Ns     []dns.RR // constant
	Extra  []dns.RR // constant
	TTL    int64    // constant

	Server      string // constant
	ServerScope int8   // constant

	Filtered        bool     // mutable
	FilteredEntries []string // mutable
	// contains filtered or unexported fields
}

RRCache is used to cache DNS data

func GetRRCache 

func GetRRCache(domain string, question dns.Type) (*RRCache, error)

GetRRCache tries to load the corresponding NameRecord from the database and convert it.

func Resolve 

func Resolve(ctx context.Context, q *Query) (rrCache *RRCache, err error)

Resolve resolves the given query for a domain and type and returns a RRCache object or nil, if the query failed.

func (*RRCache) Clean 

func (rrCache *RRCache) Clean(minExpires uint32)

Clean sets all TTLs to 17 and sets cache expiry with specified minimum.

func (*RRCache) Expired 

func (rrCache *RRCache) Expired() bool

Expired returns whether the record has expired.

func (*RRCache) ExportAllARecords 

func (rrCache *RRCache) ExportAllARecords() (ips []net.IP)

ExportAllARecords return of a list of all A and AAAA IP addresses.

func (*RRCache) Flags 

func (rrCache *RRCache) Flags() string

Flags formats ServedFromCache and RequestingNew to a condensed, flag-like format.

func (*RRCache) IsNXDomain 

func (rrCache *RRCache) IsNXDomain() bool

IsNXDomain returnes whether the result is nxdomain.

func (*RRCache) MixAnswers 

func (rrCache *RRCache) MixAnswers()

MixAnswers randomizes the answer records to allow dumb clients (who only look at the first record) to reliably connect.

func (*RRCache) RequestingNew 

func (rrCache *RRCache) RequestingNew() bool

RequestingNew informs that it has expired and new RRs are being fetched.

func (*RRCache) Save 

func (rrCache *RRCache) Save() error

Save saves the RRCache to the database as a NameRecord.

func (*RRCache) ServedFromCache 

func (rrCache *RRCache) ServedFromCache() bool

ServedFromCache marks the RRCache as served from cache.

func (*RRCache) ShallowCopy 

func (rrCache *RRCache) ShallowCopy() *RRCache

ShallowCopy returns a shallow copy of the cache. slices are not copied, but referenced.

func (*RRCache) ToNameRecord 

func (rrCache *RRCache) ToNameRecord() *NameRecord

ToNameRecord converts the RRCache to a NameRecord for cleaner persistence.

type Resolver 

type Resolver struct {
	// Server config url (and ID)
	Server string

	// Parsed config
	ServerType    string
	ServerAddress string
	ServerIP      net.IP
	ServerIPScope int8
	ServerPort    uint16

	// Special Options
	VerifyDomain string
	Search       []string
	SkipFQDN     string

	Source string

	// logic interface
	Conn ResolverConn
}

Resolver holds information about an active resolver.

func GetResolversInScope 

func GetResolversInScope(ctx context.Context, q *Query) (selected []*Resolver)

GetResolversInScope returns all resolvers that are in scope the resolve the given query and options.

func (*Resolver) String 

func (resolver *Resolver) String() string

String returns the URL representation of the resolver.

type ResolverConn 

type ResolverConn interface {
	Query(ctx context.Context, q *Query) (*RRCache, error)
	MarkFailed()
	LastFail() time.Time
}

ResolverConn is an interface to implement different types of query backends.

type Scope 

type Scope struct {
	Domain    string
	Resolvers []*Resolver
}

Scope defines a domain scope and which resolvers can resolve it.

Source Files

View all Source files

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