From 0ee29e31ddcc81f541de7459b0a5e40dfa552672 Mon Sep 17 00:00:00 2001 From: Quentin Dufour Date: Fri, 19 Nov 2021 19:54:49 +0100 Subject: Working on SFTP --- internal/encoding/ssh/filexfer/packets.go | 323 ++++++++++++++++++++++++++++++ 1 file changed, 323 insertions(+) create mode 100644 internal/encoding/ssh/filexfer/packets.go (limited to 'internal/encoding/ssh/filexfer/packets.go') diff --git a/internal/encoding/ssh/filexfer/packets.go b/internal/encoding/ssh/filexfer/packets.go new file mode 100644 index 0000000..3f24e9c --- /dev/null +++ b/internal/encoding/ssh/filexfer/packets.go @@ -0,0 +1,323 @@ +package filexfer + +import ( + "errors" + "fmt" + "io" +) + +// smallBufferSize is an initial allocation minimal capacity. +const smallBufferSize = 64 + +func newPacketFromType(typ PacketType) (Packet, error) { + switch typ { + case PacketTypeOpen: + return new(OpenPacket), nil + case PacketTypeClose: + return new(ClosePacket), nil + case PacketTypeRead: + return new(ReadPacket), nil + case PacketTypeWrite: + return new(WritePacket), nil + case PacketTypeLStat: + return new(LStatPacket), nil + case PacketTypeFStat: + return new(FStatPacket), nil + case PacketTypeSetstat: + return new(SetstatPacket), nil + case PacketTypeFSetstat: + return new(FSetstatPacket), nil + case PacketTypeOpenDir: + return new(OpenDirPacket), nil + case PacketTypeReadDir: + return new(ReadDirPacket), nil + case PacketTypeRemove: + return new(RemovePacket), nil + case PacketTypeMkdir: + return new(MkdirPacket), nil + case PacketTypeRmdir: + return new(RmdirPacket), nil + case PacketTypeRealPath: + return new(RealPathPacket), nil + case PacketTypeStat: + return new(StatPacket), nil + case PacketTypeRename: + return new(RenamePacket), nil + case PacketTypeReadLink: + return new(ReadLinkPacket), nil + case PacketTypeSymlink: + return new(SymlinkPacket), nil + case PacketTypeExtended: + return new(ExtendedPacket), nil + default: + return nil, fmt.Errorf("unexpected request packet type: %v", typ) + } +} + +// RawPacket implements the general packet format from draft-ietf-secsh-filexfer-02 +// +// RawPacket is intended for use in clients receiving responses, +// where a response will be expected to be of a limited number of types, +// and unmarshaling unknown/unexpected response packets is unnecessary. +// +// For servers expecting to receive arbitrary request packet types, +// use RequestPacket. +// +// Defined in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3 +type RawPacket struct { + PacketType PacketType + RequestID uint32 + + Data Buffer +} + +// Type returns the Type field defining the SSH_FXP_xy type for this packet. +func (p *RawPacket) Type() PacketType { + return p.PacketType +} + +// Reset clears the pointers and reference-semantic variables of RawPacket, +// releasing underlying resources, and making them and the RawPacket suitable to be reused, +// so long as no other references have been kept. +func (p *RawPacket) Reset() { + p.Data = Buffer{} +} + +// MarshalPacket returns p as a two-part binary encoding of p. +// +// The internal p.RequestID is overridden by the reqid argument. +func (p *RawPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) { + buf := NewBuffer(b) + if buf.Cap() < 9 { + buf = NewMarshalBuffer(0) + } + + buf.StartPacket(p.PacketType, reqid) + + return buf.Packet(p.Data.Bytes()) +} + +// MarshalBinary returns p as the binary encoding of p. +// +// This is a convenience implementation primarily intended for tests, +// because it is inefficient with allocations. +func (p *RawPacket) MarshalBinary() ([]byte, error) { + return ComposePacket(p.MarshalPacket(p.RequestID, nil)) +} + +// UnmarshalFrom decodes a RawPacket from the given Buffer into p. +// +// The Data field will alias the passed in Buffer, +// so the buffer passed in should not be reused before RawPacket.Reset(). +func (p *RawPacket) UnmarshalFrom(buf *Buffer) error { + typ, err := buf.ConsumeUint8() + if err != nil { + return err + } + + p.PacketType = PacketType(typ) + + if p.RequestID, err = buf.ConsumeUint32(); err != nil { + return err + } + + p.Data = *buf + return nil +} + +// UnmarshalBinary decodes a full raw packet out of the given data. +// It is assumed that the uint32(length) has already been consumed to receive the data. +// +// This is a convenience implementation primarily intended for tests, +// because this must clone the given data byte slice, +// as Data is not allowed to alias any part of the data byte slice. +func (p *RawPacket) UnmarshalBinary(data []byte) error { + clone := make([]byte, len(data)) + n := copy(clone, data) + return p.UnmarshalFrom(NewBuffer(clone[:n])) +} + +// readPacket reads a uint32 length-prefixed binary data packet from r. +// using the given byte slice as a backing array. +// +// If the packet length read from r is bigger than maxPacketLength, +// or greater than math.MaxInt32 on a 32-bit implementation, +// then a `ErrLongPacket` error will be returned. +// +// If the given byte slice is insufficient to hold the packet, +// then it will be extended to fill the packet size. +func readPacket(r io.Reader, b []byte, maxPacketLength uint32) ([]byte, error) { + if cap(b) < 4 { + // We will need allocate our own buffer just for reading the packet length. + + // However, we don’t really want to allocate an extremely narrow buffer (4-bytes), + // and cause unnecessary allocation churn from both length reads and small packet reads, + // so we use smallBufferSize from the bytes package as a reasonable guess. + + // But if callers really do want to force narrow throw-away allocation of every packet body, + // they can do so with a buffer of capacity 4. + b = make([]byte, smallBufferSize) + } + + if _, err := io.ReadFull(r, b[:4]); err != nil { + return nil, err + } + + length := unmarshalUint32(b) + if int(length) < 5 { + // Must have at least uint8(type) and uint32(request-id) + + if int(length) < 0 { + // Only possible when strconv.IntSize == 32, + // the packet length is longer than math.MaxInt32, + // and thus longer than any possible slice. + return nil, ErrLongPacket + } + + return nil, ErrShortPacket + } + if length > maxPacketLength { + return nil, ErrLongPacket + } + + if int(length) > cap(b) { + // We know int(length) must be positive, because of tests above. + b = make([]byte, length) + } + + n, err := io.ReadFull(r, b[:length]) + return b[:n], err +} + +// ReadFrom provides a simple functional packet reader, +// using the given byte slice as a backing array. +// +// To protect against potential denial of service attacks, +// if the read packet length is longer than maxPacketLength, +// then no packet data will be read, and ErrLongPacket will be returned. +// (On 32-bit int architectures, all packets >= 2^31 in length +// will return ErrLongPacket regardless of maxPacketLength.) +// +// If the read packet length is longer than cap(b), +// then a throw-away slice will allocated to meet the exact packet length. +// This can be used to limit the length of reused buffers, +// while still allowing reception of occasional large packets. +// +// The Data field may alias the passed in byte slice, +// so the byte slice passed in should not be reused before RawPacket.Reset(). +func (p *RawPacket) ReadFrom(r io.Reader, b []byte, maxPacketLength uint32) error { + b, err := readPacket(r, b, maxPacketLength) + if err != nil { + return err + } + + return p.UnmarshalFrom(NewBuffer(b)) +} + +// RequestPacket implements the general packet format from draft-ietf-secsh-filexfer-02 +// but also automatically decode/encodes valid request packets (2 < type < 100 || type == 200). +// +// RequestPacket is intended for use in servers receiving requests, +// where any arbitrary request may be received, and so decoding them automatically +// is useful. +// +// For clients expecting to receive specific response packet types, +// where automatic unmarshaling of the packet body does not make sense, +// use RawPacket. +// +// Defined in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02#section-3 +type RequestPacket struct { + RequestID uint32 + + Request Packet +} + +// Type returns the SSH_FXP_xy value associated with the underlying packet. +func (p *RequestPacket) Type() PacketType { + return p.Request.Type() +} + +// Reset clears the pointers and reference-semantic variables in RequestPacket, +// releasing underlying resources, and making them and the RequestPacket suitable to be reused, +// so long as no other references have been kept. +func (p *RequestPacket) Reset() { + p.Request = nil +} + +// MarshalPacket returns p as a two-part binary encoding of p. +// +// The internal p.RequestID is overridden by the reqid argument. +func (p *RequestPacket) MarshalPacket(reqid uint32, b []byte) (header, payload []byte, err error) { + if p.Request == nil { + return nil, nil, errors.New("empty request packet") + } + + return p.Request.MarshalPacket(reqid, b) +} + +// MarshalBinary returns p as the binary encoding of p. +// +// This is a convenience implementation primarily intended for tests, +// because it is inefficient with allocations. +func (p *RequestPacket) MarshalBinary() ([]byte, error) { + return ComposePacket(p.MarshalPacket(p.RequestID, nil)) +} + +// UnmarshalFrom decodes a RequestPacket from the given Buffer into p. +// +// The Request field may alias the passed in Buffer, (e.g. SSH_FXP_WRITE), +// so the buffer passed in should not be reused before RequestPacket.Reset(). +func (p *RequestPacket) UnmarshalFrom(buf *Buffer) error { + typ, err := buf.ConsumeUint8() + if err != nil { + return err + } + + p.Request, err = newPacketFromType(PacketType(typ)) + if err != nil { + return err + } + + if p.RequestID, err = buf.ConsumeUint32(); err != nil { + return err + } + + return p.Request.UnmarshalPacketBody(buf) +} + +// UnmarshalBinary decodes a full request packet out of the given data. +// It is assumed that the uint32(length) has already been consumed to receive the data. +// +// This is a convenience implementation primarily intended for tests, +// because this must clone the given data byte slice, +// as Request is not allowed to alias any part of the data byte slice. +func (p *RequestPacket) UnmarshalBinary(data []byte) error { + clone := make([]byte, len(data)) + n := copy(clone, data) + return p.UnmarshalFrom(NewBuffer(clone[:n])) +} + +// ReadFrom provides a simple functional packet reader, +// using the given byte slice as a backing array. +// +// To protect against potential denial of service attacks, +// if the read packet length is longer than maxPacketLength, +// then no packet data will be read, and ErrLongPacket will be returned. +// (On 32-bit int architectures, all packets >= 2^31 in length +// will return ErrLongPacket regardless of maxPacketLength.) +// +// If the read packet length is longer than cap(b), +// then a throw-away slice will allocated to meet the exact packet length. +// This can be used to limit the length of reused buffers, +// while still allowing reception of occasional large packets. +// +// The Request field may alias the passed in byte slice, +// so the byte slice passed in should not be reused before RawPacket.Reset(). +func (p *RequestPacket) ReadFrom(r io.Reader, b []byte, maxPacketLength uint32) error { + b, err := readPacket(r, b, maxPacketLength) + if err != nil { + return err + } + + return p.UnmarshalFrom(NewBuffer(b)) +} -- cgit v1.2.3