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tio.Offload.WriteGSO: reject 0-len packets, check seg lengths

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This commit is contained in:
JackDoan
2026-07-29 11:51:12 -05:00
parent 5c0f6e2b5f
commit b39bae57ec
4 changed files with 64 additions and 80 deletions
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overlay/tio/tio.go
+1 -1
View File
@@ -115,7 +115,7 @@ const (
// (mutable: the L4 checksum field must hold the pseudo-header partial, single-fold not inverted, per virtio NEEDS_CSUM semantics).
// pays are non-overlapping payload fragments whose concatenation is the full superpacket payload.
// They are read-only from the writer's perspective and must remain valid until the call returns.
// Every segment in pays except possibly the last is exactly the same size.
// Every segment in pays except possibly the last must be exactly the same size.
// proto picks the L4 protocol so the writer knows which gsoType / CsumOffset to set.
//
// Callers should also consult CapsProvider (via SupportsGSO) for the per-protocol negotiated capability:
overlay/tio/tio_gso_linux.go
+25 -32
View File
@@ -327,52 +327,45 @@ func (r *Offload) WriteGSO(hdr []byte, transportHdr []byte, pays [][]byte, proto
r.gsoIovs[2].Base = &transportHdr[0]
r.gsoIovs[2].SetLen(len(transportHdr))
// Fill out the payload iovecs and find the GSO geometry:
segSize := 0
segSize := len(pays[0])
total := len(hdr) + len(transportHdr)
n := 3
for _, p := range pays {
total += len(p)
for i, p := range pays {
if len(p) == 0 {
continue //disregard empty payloads, the kernel will reject them.
//callers already funnel zero-length frames via the not-GSO path, so this should never happen.
// The coalescers route zero-payload packets down the non-GSO path,
// so an empty fragment means the caller's accounting is broken.
return fmt.Errorf("tio: WriteGSO empty payload fragment %d of %d", i, len(pays))
} else if len(p) > segSize || (len(p) < segSize && i != len(pays)-1) {
// all segments must be the same size, except for the last one
return fmt.Errorf("tio: WriteGSO fragment %d is %dB, want %dB segments (only the last may be shorter)", i, len(p), segSize)
}
if n == 3 {
segSize = len(p)
}
r.gsoIovs[n].Base = &p[0]
r.gsoIovs[n].SetLen(len(p))
n++
total += len(p)
r.gsoIovs[3+i].Base = &p[0]
r.gsoIovs[3+i].SetLen(len(p))
}
r.gsoIovs = r.gsoIovs[:n]
segCount := n - 3
// This check keeps `total` in the uint16 range. Anything larger would wrap around and cause trouble.
if total > maxSuperpacketLen {
return fmt.Errorf("tio: WriteGSO superpacket %dB exceeds %d", total, maxSuperpacketLen)
}
// gsoType and GSOSize stay zero (GSO_NONE, 0) for single-segment, or an unknown IP version.
// A single segment ships as a plain checksummed packet (GSO_NONE, size 0).
// Multiple segments carry the real GSO type and segSize, which the loop
// above verified is the size of every fragment except possibly the last.
gsoType := uint8(unix.VIRTIO_NET_HDR_GSO_NONE)
if len(pays) > 1 {
gsoType = gsoTypeFromProto(proto, hdr[0]>>4)
}
var gsoSize uint16
if gsoType != unix.VIRTIO_NET_HDR_GSO_NONE {
gsoSize = uint16(segSize)
}
vhdr := virtio.NewHeader(
unix.VIRTIO_NET_HDR_F_NEEDS_CSUM, /*flags*/
unix.VIRTIO_NET_HDR_GSO_NONE, /*gsoType*/
gsoType, /*gsoType*/
uint16(len(hdr)+len(transportHdr)), /*hdrLen*/
0, /*gsoSize*/
gsoSize, /*gsoSize*/
uint16(len(hdr)), /*csumStart*/
csumOff, /*csumOffset*/
)
if segCount > 1 {
ipVer := hdr[0] >> 4
switch {
case proto == GSOProtoUDP && (ipVer == 4 || ipVer == 6):
vhdr.SetGSOType(unix.VIRTIO_NET_HDR_GSO_UDP_L4)
case ipVer == 6:
vhdr.SetGSOType(unix.VIRTIO_NET_HDR_GSO_TCPV6)
case ipVer == 4:
vhdr.SetGSOType(unix.VIRTIO_NET_HDR_GSO_TCPV4)
}
if vhdr.GSOType() != unix.VIRTIO_NET_HDR_GSO_NONE {
vhdr.GSOSize = uint16(segSize)
}
}
vhdr.Encode(r.gsoHdrBuf[:])
_, err := r.rawWrite(r.gsoIovs)
overlay/tio/tun_linux_offload.go
+14
View File
@@ -25,6 +25,20 @@ func protoFromGSOType(t uint8) (GSOProto, error) {
}
}
// gsoTypeFromProto is the reverse of protoFromGSOType
func gsoTypeFromProto(proto GSOProto, ipVer uint8) uint8 {
switch {
case proto == GSOProtoUDP && (ipVer == 4 || ipVer == 6):
return unix.VIRTIO_NET_HDR_GSO_UDP_L4
case ipVer == 6:
return unix.VIRTIO_NET_HDR_GSO_TCPV6
case ipVer == 4:
return unix.VIRTIO_NET_HDR_GSO_TCPV4
default:
return unix.VIRTIO_NET_HDR_GSO_NONE
}
}
// SegmentSuperpacket invokes fn once per segment of pkt.
// For non-GSO pkts fn is called once with pkt.Bytes.
// For GSO/USO superpackets, fn is called once per segment with a slice of pkt.Bytes holding that segment's plaintext
overlay/tio/tun_linux_offload_test.go
+24 -47
View File
@@ -744,38 +744,6 @@ func TestSegmentSuperpacketNoAlloc(t *testing.T) {
}
}
// TestWriteGSOSkipsEmptyPayloads is the defense-in-depth guard for the
// zero-length UDP DoS: a payload fragment of length zero would make &p[0]
// panic (index-out-of-range) when building the iovec array. WriteGSO must
// skip empties instead. We write to /dev/null so the writev always succeeds
// synchronously; the point is simply that neither call panics.
func TestWriteGSOSkipsEmptyPayloads(t *testing.T) {
fd, err := unix.Open("/dev/null", os.O_WRONLY, 0)
if err != nil {
t.Fatalf("open /dev/null: %v", err)
}
t.Cleanup(func() { _ = unix.Close(fd) })
o := &Offload{fd: fd, gsoIovs: make([]unix.Iovec, 2, gsoMaxIovs)}
o.gsoIovs[0].Base = &o.gsoHdrBuf[0]
o.gsoIovs[0].SetLen(virtio.Size)
ipHdr := make([]byte, 20)
ipHdr[0] = 0x45 // IPv4, IHL 5
udpHdr := make([]byte, 8)
// Sole payload empty: exercises the all-empty skip (n stays at 3).
if err := o.WriteGSO(ipHdr, udpHdr, [][]byte{{}}, GSOProtoUDP); err != nil {
t.Fatalf("WriteGSO with a single empty payload: %v", err)
}
// Empty mixed with a real fragment: exercises the index-drift skip so a
// later non-empty payload still lands in the right iovec slot.
real := make([]byte, 1200)
if err := o.WriteGSO(ipHdr, udpHdr, [][]byte{real, {}}, GSOProtoUDP); err != nil {
t.Fatalf("WriteGSO with a trailing empty payload: %v", err)
}
}
// buildTSOv6 builds a synthetic IPv6/TCP TSO superpacket with payLen bytes
// of payload, segmented at gso. Returns the packet bytes only; the
// virtio_net_hdr is the caller's responsibility.
@@ -943,12 +911,12 @@ func TestOffloadWriteZeroLength(t *testing.T) {
}
}
// TestWriteGSOLeadingEmptyFragmentGeometry: gso_size must be derived from
// the first non-empty fragment. Deriving it from pays[0] stamped a
// superpacket header with gso_size == 0 when the leading fragment was
// empty -- the kernel rejects that with EINVAL and the burst is lost.
// Write through a pipe and decode the vnet header the kernel would see.
func TestWriteGSOLeadingEmptyFragmentGeometry(t *testing.T) {
// TestWriteGSOSuperpacketGeometry decodes the vnet header the kernel would see for a multi-segment write:
// the GSO type must match the proto and IP version
// gso_size must be the per-segment size (the kernel rejects a superpacket with gso_size == 0),
// and the csum fields must point at the transport header's checksum slot.
// Write through a pipe so the bytes can be read back and decoded.
func TestWriteGSOSuperpacketGeometry(t *testing.T) {
var pfds [2]int
if err := unix.Pipe(pfds[:]); err != nil {
t.Fatalf("pipe: %v", err)
@@ -964,8 +932,8 @@ func TestWriteGSOLeadingEmptyFragmentGeometry(t *testing.T) {
udpHdr := make([]byte, 8)
seg := make([]byte, 1200)
if err := o.WriteGSO(ipHdr, udpHdr, [][]byte{{}, seg, seg}, GSOProtoUDP); err != nil {
t.Fatalf("WriteGSO with leading empty fragment: %v", err)
if err := o.WriteGSO(ipHdr, udpHdr, [][]byte{seg, seg}, GSOProtoUDP); err != nil {
t.Fatalf("WriteGSO: %v", err)
}
buf := make([]byte, virtio.Size+len(ipHdr)+len(udpHdr)+2*len(seg)+64)
@@ -979,18 +947,20 @@ func TestWriteGSOLeadingEmptyFragmentGeometry(t *testing.T) {
t.Errorf("gsoType=%d want UDP_L4", vhdr.GSOType())
}
if vhdr.GSOSize != 1200 {
t.Errorf("GSOSize=%d want 1200 (first non-empty fragment)", vhdr.GSOSize)
t.Errorf("GSOSize=%d want 1200 (per-segment size from pays[0])", vhdr.GSOSize)
}
if vhdr.HdrLen != uint16(len(ipHdr)+len(udpHdr)) {
t.Errorf("HdrLen=%d want %d", vhdr.HdrLen, len(ipHdr)+len(udpHdr))
}
if vhdr.CsumStart != uint16(len(ipHdr)) || vhdr.CsumOffset != 6 {
t.Errorf("csum start/offset = %d/%d want %d/6", vhdr.CsumStart, vhdr.CsumOffset, len(ipHdr))
}
if want := virtio.Size + len(ipHdr) + len(udpHdr) + 2*len(seg); n != want {
t.Errorf("wrote %d bytes want %d (empty fragment must not add an iovec)", n, want)
t.Errorf("wrote %d bytes want %d", n, want)
}
}
// TestWriteGSORejectsBadGeometry pins the length-check contract: malformed
// geometry must fail loudly instead of silently succeeding (the old empty-
// header early-out returned nil and dropped the payload), and nothing may
// reach the u16 virtio fields or the kernel's csum_start+csum_offset write
// without covering them.
// TestWriteGSORejectsBadGeometry pins the length-check contracts
func TestWriteGSORejectsBadGeometry(t *testing.T) {
fd, err := unix.Open("/dev/null", os.O_WRONLY, 0)
if err != nil {
@@ -1019,6 +989,13 @@ func TestWriteGSORejectsBadGeometry(t *testing.T) {
{"udp-transport-too-short-for-csum", ipHdr, udpHdr[:6], [][]byte{seg}, GSOProtoUDP, true},
{"tcp-transport-too-short-for-csum", ipHdr, tcpHdr[:16], [][]byte{seg}, GSOProtoTCP, true},
{"superpacket-over-65535", ipHdr, tcpHdr, [][]byte{make([]byte, 40000), make([]byte, 40000)}, GSOProtoTCP, true},
{"sole-payload-empty", ipHdr, udpHdr, [][]byte{{}}, GSOProtoUDP, true},
{"leading-empty-fragment", ipHdr, udpHdr, [][]byte{{}, seg, seg}, GSOProtoUDP, true},
{"trailing-empty-fragment", ipHdr, tcpHdr, [][]byte{seg, {}}, GSOProtoTCP, true},
{"oversize-middle-fragment", ipHdr, udpHdr, [][]byte{seg, make([]byte, 1201), seg}, GSOProtoUDP, true},
{"undersize-middle-fragment", ipHdr, udpHdr, [][]byte{seg, make([]byte, 100), seg}, GSOProtoUDP, true},
{"oversize-last-fragment", ipHdr, tcpHdr, [][]byte{seg, make([]byte, 1201)}, GSOProtoTCP, true},
{"short-last-fragment-ok", ipHdr, udpHdr, [][]byte{seg, seg, make([]byte, 100)}, GSOProtoUDP, false},
{"no-pays-noop", ipHdr, udpHdr, nil, GSOProtoUDP, false},
{"valid-udp", ipHdr, udpHdr, [][]byte{seg, seg}, GSOProtoUDP, false},
{"valid-tcp", ipHdr, tcpHdr, [][]byte{seg, seg}, GSOProtoTCP, false},