Protect against stray EOFs #44
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
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@@ -20,27 +20,29 @@ const maxHeaderSize = 9 | |
| // the most common readers we encounter in this library for a significant | ||
| // performance boost. | ||
| func discard(br io.Reader, n int) error { | ||
| var err error | ||
| switch r := br.(type) { | ||
| case *bytes.Buffer: | ||
| buf := r.Next(n) | ||
| if len(buf) < n { | ||
| err = io.ErrUnexpectedEOF | ||
| } | ||
| case *bytes.Reader: | ||
| if r.Len() < n { | ||
| _, _ = r.Seek(0, io.SeekEnd) | ||
| err = io.ErrUnexpectedEOF | ||
| } else { | ||
| _, err = r.Seek(int64(n), io.SeekCurrent) | ||
| } | ||
| case *bufio.Reader: | ||
| _, err = r.Discard(n) | ||
| default: | ||
| _, err = io.CopyN(ioutil.Discard, br, int64(n)) | ||
| } | ||
| if err == io.EOF { | ||
| err = io.ErrUnexpectedEOF | ||
| } | ||
| return err | ||
| } | ||
|
|
||
| func ScanForLinks(br io.Reader, cb func(cid.Cid)) error { | ||
|
|
@@ -73,7 +75,7 @@ func ScanForLinks(br io.Reader, cb func(cid.Cid)) error { | |
| return fmt.Errorf("string in cbor input too long") | ||
| } | ||
|
|
||
| if err := ReadExact(br, scratch[:extra]); err != nil { | ||
| return err | ||
| } | ||
|
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||
|
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@@ -172,7 +174,7 @@ func (d *Deferred) UnmarshalCBOR(br io.Reader) error { | |
| // Copy the bytes | ||
| limitedReader.N = int64(extra) | ||
| buf.Grow(int(extra)) | ||
| if n, err := buf.ReadFrom(&limitedReader); err != nil && err != io.EOF { | ||
|
There was a problem hiding this comment. buf.ReadFrom doesn't return io.EOF: https://pkg.go.dev/bytes@go1.17.6#Buffer.ReadFrom |
||
| return err | ||
| } else if n < int64(extra) { | ||
| return io.ErrUnexpectedEOF | ||
|
|
@@ -213,7 +215,7 @@ func readByte(r io.Reader) (byte, error) { | |
| return r.ReadByte() | ||
| } | ||
| var buf [1]byte | ||
| err := ReadExact(r, buf[:1]) | ||
| return buf[0], err | ||
| } | ||
|
|
||
|
|
@@ -240,27 +242,27 @@ func CborReadHeader(br io.Reader) (byte, uint64, error) { | |
| return maj, uint64(next), nil | ||
| case low == 25: | ||
| scratch := make([]byte, 2) | ||
| if err := ReadExact(br, scratch); err != nil { | ||
| return 0, 0, err | ||
| } | ||
| val := uint64(binary.BigEndian.Uint16(scratch)) | ||
| if val <= math.MaxUint8 { | ||
| return 0, 0, fmt.Errorf("cbor input was not canonical (lval 25 with value <= MaxUint8)") | ||
| } | ||
| return maj, val, nil | ||
| case low == 26: | ||
| scratch := make([]byte, 4) | ||
| if err := ReadExact(br, scratch); err != nil { | ||
| return 0, 0, err | ||
| } | ||
| val := uint64(binary.BigEndian.Uint32(scratch)) | ||
| if val <= math.MaxUint16 { | ||
| return 0, 0, fmt.Errorf("cbor input was not canonical (lval 26 with value <= MaxUint16)") | ||
| } | ||
| return maj, val, nil | ||
| case low == 27: | ||
| scratch := make([]byte, 8) | ||
| if err := ReadExact(br, scratch); err != nil { | ||
| return 0, 0, err | ||
| } | ||
| val := binary.BigEndian.Uint64(scratch) | ||
|
|
@@ -276,6 +278,7 @@ func CborReadHeader(br io.Reader) (byte, uint64, error) { | |
| func readByteBuf(r io.Reader, scratch []byte) (byte, error) { | ||
| // Reading a single byte from these buffers is much faster than copying | ||
| // into a slice. | ||
| // None of these will return EOF if they also read a byte. | ||
| switch r := r.(type) { | ||
| case *bytes.Buffer: | ||
| return r.ReadByte() | ||
|
|
@@ -285,13 +288,23 @@ func readByteBuf(r io.Reader, scratch []byte) (byte, error) { | |
| return r.ReadByte() | ||
| } | ||
| n, err := r.Read(scratch[:1]) | ||
| if err == io.EOF { | ||
| // Read can return EOF, even if it reads data. Furthermore, we | ||
| // never want to return EOF on actual error cases (so we return | ||
| // "unexpected eof"). | ||
| if n == 1 { | ||
| err = nil | ||
| } else { | ||
| err = io.ErrUnexpectedEOF | ||
| } | ||
| } | ||
| if err != nil { | ||
| return 0, err | ||
| } | ||
| if n != 1 { | ||
| return 0, fmt.Errorf("failed to read a byte") | ||
| } | ||
| return scratch[0], nil | ||
| } | ||
|
|
||
| // same as the above, just tries to allocate less by using a passed in scratch buffer | ||
|
|
@@ -317,7 +330,7 @@ func CborReadHeaderBuf(br io.Reader, scratch []byte) (byte, uint64, error) { | |
| } | ||
| return maj, uint64(next), nil | ||
| case low == 25: | ||
| if err := ReadExact(br, scratch[:2]); err != nil { | ||
| return 0, 0, err | ||
| } | ||
| val := uint64(binary.BigEndian.Uint16(scratch[:2])) | ||
|
|
@@ -326,7 +339,7 @@ func CborReadHeaderBuf(br io.Reader, scratch []byte) (byte, uint64, error) { | |
| } | ||
| return maj, val, nil | ||
| case low == 26: | ||
| if err := ReadExact(br, scratch[:4]); err != nil { | ||
| return 0, 0, err | ||
| } | ||
| val := uint64(binary.BigEndian.Uint32(scratch[:4])) | ||
|
|
@@ -335,7 +348,7 @@ func CborReadHeaderBuf(br io.Reader, scratch []byte) (byte, uint64, error) { | |
| } | ||
| return maj, val, nil | ||
| case low == 27: | ||
| if err := ReadExact(br, scratch[:8]); err != nil { | ||
| return 0, 0, err | ||
| } | ||
| val := binary.BigEndian.Uint64(scratch[:8]) | ||
|
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@@ -474,7 +487,7 @@ func ReadByteArray(br io.Reader, maxlen uint64) ([]byte, error) { | |
| } | ||
|
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||
| buf := make([]byte, extra) | ||
| if err := ReadExact(br, buf); err != nil { | ||
| return nil, err | ||
| } | ||
|
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||
|
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@@ -514,8 +527,7 @@ func ReadString(r io.Reader) (string, error) { | |
| } | ||
|
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| buf := make([]byte, l) | ||
| if err := ReadExact(r, buf); err != nil { | ||
| return "", err | ||
| } | ||
|
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@@ -537,8 +549,7 @@ func ReadStringBuf(r io.Reader, scratch []byte) (string, error) { | |
| } | ||
|
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| buf := make([]byte, l) | ||
| if err := ReadExact(r, buf); err != nil { | ||
| return "", err | ||
| } | ||
|
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@@ -623,6 +634,16 @@ func WriteCidBuf(buf []byte, w io.Writer, c cid.Cid) error { | |
| return nil | ||
| } | ||
|
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| // ReadExact is equivalent to ReadFull except that it returns ErrUnexpectedEOF when it reads | ||
| // nothing, instead of just EOF. | ||
| func ReadExact(r io.Reader, buf []byte) error { | ||
| _, err := io.ReadFull(r, buf) | ||
| if err == io.EOF { | ||
| err = io.ErrUnexpectedEOF | ||
| } | ||
| return err | ||
| } | ||
|
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| type CborBool bool | ||
|
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| func (cb *CborBool) MarshalCBOR(w io.Writer) error { | ||
|
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Without knowing this code it is hard to know which functions are safe from returning io.EOFs, for example
CborReadHeaderBufabove does not check for EOFs but from the names and arguments it seems like it could return them. I don't know if this is actually what we should do but here and indiscardit would help me be more sure EOF handling is correct if we did error escalation in a defer statement.