diff options
Diffstat (limited to 'pkg/tcpip/header/ndp_options.go')
| -rw-r--r-- | pkg/tcpip/header/ndp_options.go | 441 |
1 files changed, 429 insertions, 12 deletions
diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go index b28bde15b..06e0bace2 100644 --- a/pkg/tcpip/header/ndp_options.go +++ b/pkg/tcpip/header/ndp_options.go @@ -15,6 +15,11 @@ package header import ( + "encoding/binary" + "errors" + "math" + "time" + "gvisor.dev/gvisor/pkg/tcpip" ) @@ -27,15 +32,226 @@ const ( // Link Layer Option for an Ethernet address. ndpTargetEthernetLinkLayerAddressSize = 8 + // NDPPrefixInformationType is the type of the Prefix Information + // option, as per RFC 4861 section 4.6.2. + NDPPrefixInformationType = 3 + + // ndpPrefixInformationLength is the expected length, in bytes, of the + // body of an NDP Prefix Information option, as per RFC 4861 section + // 4.6.2 which specifies that the Length field is 4. Given this, the + // expected length, in bytes, is 30 becuase 4 * lengthByteUnits (8) - 2 + // (Type & Length) = 30. + ndpPrefixInformationLength = 30 + + // ndpPrefixInformationPrefixLengthOffset is the offset of the Prefix + // Length field within an NDPPrefixInformation. + ndpPrefixInformationPrefixLengthOffset = 0 + + // ndpPrefixInformationFlagsOffset is the offset of the flags byte + // within an NDPPrefixInformation. + ndpPrefixInformationFlagsOffset = 1 + + // ndpPrefixInformationOnLinkFlagMask is the mask of the On-Link Flag + // field in the flags byte within an NDPPrefixInformation. + ndpPrefixInformationOnLinkFlagMask = (1 << 7) + + // ndpPrefixInformationAutoAddrConfFlagMask is the mask of the + // Autonomous Address-Configuration flag field in the flags byte within + // an NDPPrefixInformation. + ndpPrefixInformationAutoAddrConfFlagMask = (1 << 6) + + // ndpPrefixInformationReserved1FlagsMask is the mask of the Reserved1 + // field in the flags byte within an NDPPrefixInformation. + ndpPrefixInformationReserved1FlagsMask = 63 + + // ndpPrefixInformationValidLifetimeOffset is the start of the 4-byte + // Valid Lifetime field within an NDPPrefixInformation. + ndpPrefixInformationValidLifetimeOffset = 2 + + // ndpPrefixInformationPreferredLifetimeOffset is the start of the + // 4-byte Preferred Lifetime field within an NDPPrefixInformation. + ndpPrefixInformationPreferredLifetimeOffset = 6 + + // ndpPrefixInformationReserved2Offset is the start of the 4-byte + // Reserved2 field within an NDPPrefixInformation. + ndpPrefixInformationReserved2Offset = 10 + + // ndpPrefixInformationReserved2Length is the length of the Reserved2 + // field. + // + // It is 4 bytes. + ndpPrefixInformationReserved2Length = 4 + + // ndpPrefixInformationPrefixOffset is the start of the Prefix field + // within an NDPPrefixInformation. + ndpPrefixInformationPrefixOffset = 14 + + // NDPRecursiveDNSServerOptionType is the type of the Recursive DNS + // Server option, as per RFC 8106 section 5.1. + NDPRecursiveDNSServerOptionType = 25 + + // ndpRecursiveDNSServerLifetimeOffset is the start of the 4-byte + // Lifetime field within an NDPRecursiveDNSServer. + ndpRecursiveDNSServerLifetimeOffset = 2 + + // ndpRecursiveDNSServerAddressesOffset is the start of the addresses + // for IPv6 Recursive DNS Servers within an NDPRecursiveDNSServer. + ndpRecursiveDNSServerAddressesOffset = 6 + + // minNDPRecursiveDNSServerLength is the minimum NDP Recursive DNS + // Server option's length field value when it contains at least one + // IPv6 address. + minNDPRecursiveDNSServerLength = 3 + // lengthByteUnits is the multiplier factor for the Length field of an // NDP option. That is, the length field for NDP options is in units of // 8 octets, as per RFC 4861 section 4.6. lengthByteUnits = 8 ) +var ( + // NDPInfiniteLifetime is a value that represents infinity for the + // 4-byte lifetime fields found in various NDP options. Its value is + // (2^32 - 1)s = 4294967295s. + // + // This is a variable instead of a constant so that tests can change + // this value to a smaller value. It should only be modified by tests. + NDPInfiniteLifetime = time.Second * math.MaxUint32 +) + +// NDPOptionIterator is an iterator of NDPOption. +// +// Note, between when an NDPOptionIterator is obtained and last used, no changes +// to the NDPOptions may happen. Doing so may cause undefined and unexpected +// behaviour. It is fine to obtain an NDPOptionIterator, iterate over the first +// few NDPOption then modify the backing NDPOptions so long as the +// NDPOptionIterator obtained before modification is no longer used. +type NDPOptionIterator struct { + // The NDPOptions this NDPOptionIterator is iterating over. + opts NDPOptions +} + +// Potential errors when iterating over an NDPOptions. +var ( + ErrNDPOptBufExhausted = errors.New("Buffer unexpectedly exhausted") + ErrNDPOptZeroLength = errors.New("NDP option has zero-valued Length field") + ErrNDPOptMalformedBody = errors.New("NDP option has a malformed body") + ErrNDPInvalidLength = errors.New("NDP option's Length value is invalid as per relevant RFC") +) + +// Next returns the next element in the backing NDPOptions, or true if we are +// done, or false if an error occured. +// +// The return can be read as option, done, error. Note, option should only be +// used if done is false and error is nil. +func (i *NDPOptionIterator) Next() (NDPOption, bool, error) { + for { + // Do we still have elements to look at? + if len(i.opts) == 0 { + return nil, true, nil + } + + // Do we have enough bytes for an NDP option that has a Length + // field of at least 1? Note, 0 in the Length field is invalid. + if len(i.opts) < lengthByteUnits { + return nil, true, ErrNDPOptBufExhausted + } + + // Get the Type field. + t := i.opts[0] + + // Get the Length field. + l := i.opts[1] + + // This would indicate an erroneous NDP option as the Length + // field should never be 0. + if l == 0 { + return nil, true, ErrNDPOptZeroLength + } + + // How many bytes are in the option body? + numBytes := int(l) * lengthByteUnits + numBodyBytes := numBytes - 2 + + potentialBody := i.opts[2:] + + // This would indicate an erroenous NDPOptions buffer as we ran + // out of the buffer in the middle of an NDP option. + if left := len(potentialBody); left < numBodyBytes { + return nil, true, ErrNDPOptBufExhausted + } + + // Get only the options body, leaving the rest of the options + // buffer alone. + body := potentialBody[:numBodyBytes] + + // Update opts with the remaining options body. + i.opts = i.opts[numBytes:] + + switch t { + case NDPTargetLinkLayerAddressOptionType: + return NDPTargetLinkLayerAddressOption(body), false, nil + + case NDPPrefixInformationType: + // Make sure the length of a Prefix Information option + // body is ndpPrefixInformationLength, as per RFC 4861 + // section 4.6.2. + if numBodyBytes != ndpPrefixInformationLength { + return nil, true, ErrNDPOptMalformedBody + } + + return NDPPrefixInformation(body), false, nil + + case NDPRecursiveDNSServerOptionType: + // RFC 8106 section 5.3.1 outlines that the RDNSS option + // must have a minimum length of 3 so it contains at + // least one IPv6 address. + if l < minNDPRecursiveDNSServerLength { + return nil, true, ErrNDPInvalidLength + } + + opt := NDPRecursiveDNSServer(body) + if len(opt.Addresses()) == 0 { + return nil, true, ErrNDPOptMalformedBody + } + + return opt, false, nil + + default: + // We do not yet recognize the option, just skip for + // now. This is okay because RFC 4861 allows us to + // skip/ignore any unrecognized options. However, + // we MUST recognized all the options in RFC 4861. + // + // TODO(b/141487990): Handle all NDP options as defined + // by RFC 4861. + } + } +} + // NDPOptions is a buffer of NDP options as defined by RFC 4861 section 4.6. type NDPOptions []byte +// Iter returns an iterator of NDPOption. +// +// If check is true, Iter will do an integrity check on the options by iterating +// over it and returning an error if detected. +// +// See NDPOptionIterator for more information. +func (b NDPOptions) Iter(check bool) (NDPOptionIterator, error) { + it := NDPOptionIterator{opts: b} + + if check { + for it2 := it; true; { + if _, done, err := it2.Next(); err != nil || done { + return it, err + } + } + } + + return it, nil +} + // Serialize serializes the provided list of NDP options into o. // // Note, b must be of sufficient size to hold all the options in s. See @@ -75,15 +291,15 @@ func (b NDPOptions) Serialize(s NDPOptionsSerializer) int { return done } -// ndpOption is the set of functions to be implemented by all NDP option types. -type ndpOption interface { - // Type returns the type of this ndpOption. +// NDPOption is the set of functions to be implemented by all NDP option types. +type NDPOption interface { + // Type returns the type of the receiver. Type() uint8 - // Length returns the length of the body of this ndpOption, in bytes. + // Length returns the length of the body of the receiver, in bytes. Length() int - // serializeInto serializes this ndpOption into the provided byte + // serializeInto serializes the receiver into the provided byte // buffer. // // Note, the caller MUST provide a byte buffer with size of at least @@ -92,15 +308,15 @@ type ndpOption interface { // buffer is not of sufficient size. // // serializeInto will return the number of bytes that was used to - // serialize this ndpOption. Implementers must only use the number of - // bytes required to serialize this ndpOption. Callers MAY provide a + // serialize the receiver. Implementers must only use the number of + // bytes required to serialize the receiver. Callers MAY provide a // larger buffer than required to serialize into. serializeInto([]byte) int } // paddedLength returns the length of o, in bytes, with any padding bytes, if // required. -func paddedLength(o ndpOption) int { +func paddedLength(o NDPOption) int { l := o.Length() if l == 0 { @@ -139,7 +355,7 @@ func paddedLength(o ndpOption) int { } // NDPOptionsSerializer is a serializer for NDP options. -type NDPOptionsSerializer []ndpOption +type NDPOptionsSerializer []NDPOption // Length returns the total number of bytes required to serialize. func (b NDPOptionsSerializer) Length() int { @@ -154,19 +370,220 @@ func (b NDPOptionsSerializer) Length() int { // NDPTargetLinkLayerAddressOption is the NDP Target Link Layer Option // as defined by RFC 4861 section 4.6.1. +// +// It is the first X bytes following the NDP option's Type and Length field +// where X is the value in Length multiplied by lengthByteUnits - 2 bytes. type NDPTargetLinkLayerAddressOption tcpip.LinkAddress -// Type implements ndpOption.Type. +// Type implements NDPOption.Type. func (o NDPTargetLinkLayerAddressOption) Type() uint8 { return NDPTargetLinkLayerAddressOptionType } -// Length implements ndpOption.Length. +// Length implements NDPOption.Length. func (o NDPTargetLinkLayerAddressOption) Length() int { return len(o) } -// serializeInto implements ndpOption.serializeInto. +// serializeInto implements NDPOption.serializeInto. func (o NDPTargetLinkLayerAddressOption) serializeInto(b []byte) int { return copy(b, o) } + +// EthernetAddress will return an ethernet (MAC) address if the +// NDPTargetLinkLayerAddressOption's body has at minimum EthernetAddressSize +// bytes. If the body has more than EthernetAddressSize bytes, only the first +// EthernetAddressSize bytes are returned as that is all that is needed for an +// Ethernet address. +func (o NDPTargetLinkLayerAddressOption) EthernetAddress() tcpip.LinkAddress { + if len(o) >= EthernetAddressSize { + return tcpip.LinkAddress(o[:EthernetAddressSize]) + } + + return tcpip.LinkAddress([]byte(nil)) +} + +// NDPPrefixInformation is the NDP Prefix Information option as defined by +// RFC 4861 section 4.6.2. +// +// The length, in bytes, of a valid NDP Prefix Information option body MUST be +// ndpPrefixInformationLength bytes. +type NDPPrefixInformation []byte + +// Type implements NDPOption.Type. +func (o NDPPrefixInformation) Type() uint8 { + return NDPPrefixInformationType +} + +// Length implements NDPOption.Length. +func (o NDPPrefixInformation) Length() int { + return ndpPrefixInformationLength +} + +// serializeInto implements NDPOption.serializeInto. +func (o NDPPrefixInformation) serializeInto(b []byte) int { + used := copy(b, o) + + // Zero out the Reserved1 field. + b[ndpPrefixInformationFlagsOffset] &^= ndpPrefixInformationReserved1FlagsMask + + // Zero out the Reserved2 field. + reserved2 := b[ndpPrefixInformationReserved2Offset:][:ndpPrefixInformationReserved2Length] + for i := range reserved2 { + reserved2[i] = 0 + } + + return used +} + +// PrefixLength returns the value in the number of leading bits in the Prefix +// that are valid. +// +// Valid values are in the range [0, 128], but o may not always contain valid +// values. It is up to the caller to valdiate the Prefix Information option. +func (o NDPPrefixInformation) PrefixLength() uint8 { + return o[ndpPrefixInformationPrefixLengthOffset] +} + +// OnLinkFlag returns true of the prefix is considered on-link. On-link means +// that a forwarding node is not needed to send packets to other nodes on the +// same prefix. +// +// Note, when this function returns false, no statement is made about the +// on-link property of a prefix. That is, if OnLinkFlag returns false, the +// caller MUST NOT conclude that the prefix is off-link and MUST NOT update any +// previously stored state for this prefix about its on-link status. +func (o NDPPrefixInformation) OnLinkFlag() bool { + return o[ndpPrefixInformationFlagsOffset]&ndpPrefixInformationOnLinkFlagMask != 0 +} + +// AutonomousAddressConfigurationFlag returns true if the prefix can be used for +// Stateless Address Auto-Configuration (as specified in RFC 4862). +func (o NDPPrefixInformation) AutonomousAddressConfigurationFlag() bool { + return o[ndpPrefixInformationFlagsOffset]&ndpPrefixInformationAutoAddrConfFlagMask != 0 +} + +// ValidLifetime returns the length of time that the prefix is valid for the +// purpose of on-link determination. This value is relative to the send time of +// the packet that the Prefix Information option was present in. +// +// Note, a value of 0 implies the prefix should not be considered as on-link, +// and a value of infinity/forever is represented by +// NDPInfiniteLifetime. +func (o NDPPrefixInformation) ValidLifetime() time.Duration { + // The field is the time in seconds, as per RFC 4861 section 4.6.2. + return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpPrefixInformationValidLifetimeOffset:])) +} + +// PreferredLifetime returns the length of time that an address generated from +// the prefix via Stateless Address Auto-Configuration remains preferred. This +// value is relative to the send time of the packet that the Prefix Information +// option was present in. +// +// Note, a value of 0 implies that addresses generated from the prefix should +// no longer remain preferred, and a value of infinity is represented by +// NDPInfiniteLifetime. +// +// Also note that the value of this field MUST NOT exceed the Valid Lifetime +// field to avoid preferring addresses that are no longer valid, for the +// purpose of Stateless Address Auto-Configuration. +func (o NDPPrefixInformation) PreferredLifetime() time.Duration { + // The field is the time in seconds, as per RFC 4861 section 4.6.2. + return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpPrefixInformationPreferredLifetimeOffset:])) +} + +// Prefix returns an IPv6 address or a prefix of an IPv6 address. The Prefix +// Length field (see NDPPrefixInformation.PrefixLength) contains the number +// of valid leading bits in the prefix. +// +// Hosts SHOULD ignore an NDP Prefix Information option where the Prefix field +// holds the link-local prefix (fe80::). +func (o NDPPrefixInformation) Prefix() tcpip.Address { + return tcpip.Address(o[ndpPrefixInformationPrefixOffset:][:IPv6AddressSize]) +} + +// Subnet returns the Prefix field and Prefix Length field represented in a +// tcpip.Subnet. +func (o NDPPrefixInformation) Subnet() tcpip.Subnet { + addrWithPrefix := tcpip.AddressWithPrefix{ + Address: o.Prefix(), + PrefixLen: int(o.PrefixLength()), + } + return addrWithPrefix.Subnet() +} + +// NDPRecursiveDNSServer is the NDP Recursive DNS Server option, as defined by +// RFC 8106 section 5.1. +// +// To make sure that the option meets its minimum length and does not end in the +// middle of a DNS server's IPv6 address, the length of a valid +// NDPRecursiveDNSServer must meet the following constraint: +// (Length - ndpRecursiveDNSServerAddressesOffset) % IPv6AddressSize == 0 +type NDPRecursiveDNSServer []byte + +// Type returns the type of an NDP Recursive DNS Server option. +// +// Type implements NDPOption.Type. +func (NDPRecursiveDNSServer) Type() uint8 { + return NDPRecursiveDNSServerOptionType +} + +// Length implements NDPOption.Length. +func (o NDPRecursiveDNSServer) Length() int { + return len(o) +} + +// serializeInto implements NDPOption.serializeInto. +func (o NDPRecursiveDNSServer) serializeInto(b []byte) int { + used := copy(b, o) + + // Zero out the reserved bytes that are before the Lifetime field. + for i := 0; i < ndpRecursiveDNSServerLifetimeOffset; i++ { + b[i] = 0 + } + + return used +} + +// Lifetime returns the length of time that the DNS server addresses +// in this option may be used for name resolution. +// +// Note, a value of 0 implies the addresses should no longer be used, +// and a value of infinity/forever is represented by NDPInfiniteLifetime. +// +// Lifetime may panic if o does not have enough bytes to hold the Lifetime +// field. +func (o NDPRecursiveDNSServer) Lifetime() time.Duration { + // The field is the time in seconds, as per RFC 8106 section 5.1. + return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpRecursiveDNSServerLifetimeOffset:])) +} + +// Addresses returns the recursive DNS server IPv6 addresses that may be +// used for name resolution. +// +// Note, some of the addresses returned MAY be link-local addresses. +// +// Addresses may panic if o does not hold valid IPv6 addresses. +func (o NDPRecursiveDNSServer) Addresses() []tcpip.Address { + l := len(o) + if l < ndpRecursiveDNSServerAddressesOffset { + return nil + } + + l -= ndpRecursiveDNSServerAddressesOffset + if l%IPv6AddressSize != 0 { + return nil + } + + buf := o[ndpRecursiveDNSServerAddressesOffset:] + var addrs []tcpip.Address + for len(buf) > 0 { + addr := tcpip.Address(buf[:IPv6AddressSize]) + if !IsV6UnicastAddress(addr) { + return nil + } + addrs = append(addrs, addr) + buf = buf[IPv6AddressSize:] + } + return addrs +} |