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Fix bug in FOU netlink parser #827

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Fix bug in FOU netlink parser #827

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19 changes: 12 additions & 7 deletions fou_linux.go
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
//go:build linux
// +build linux

package netlink
Expand Down Expand Up @@ -171,36 +172,40 @@ func (h *Handle) FouList(fam int) ([]Fou, error) {
func deserializeFouMsg(msg []byte) (Fou, error) {
// we'll skip to byte 4 to first attribute
msg = msg[3:]
var shift int
fou := Fou{}

for {
// attribute header is at least 16 bits
// attribute header is at least 32 bits (16 bit type + 16 bit length)
if len(msg) < 4 {
return fou, ErrAttrHeaderTruncated
}

lgt := int(binary.BigEndian.Uint16(msg[0:2]))
if len(msg) < lgt+4 {
lgt4 := lgt & (^0x3)

// Padding to 4 bytes according to netlink man7
lgtPad := lgt4 + 4
if lgt4 == lgt {
lgtPad = lgt
}

if len(msg) < lgtPad {
return fou, ErrAttrBodyTruncated
}
attr := binary.BigEndian.Uint16(msg[2:4])

shift = lgt + 3
switch attr {
case FOU_ATTR_AF:
fou.Family = int(msg[5])
case FOU_ATTR_PORT:
fou.Port = int(binary.BigEndian.Uint16(msg[5:7]))
// port is 2 bytes
shift = lgt + 2
case FOU_ATTR_IPPROTO:
fou.Protocol = int(msg[5])
case FOU_ATTR_TYPE:
fou.EncapType = int(msg[5])
}

msg = msg[shift:]
msg = msg[lgtPad:]

if len(msg) < 4 {
break
Expand Down
3 changes: 2 additions & 1 deletion fou_test.go
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
//go:build linux
// +build linux

package netlink
Expand Down Expand Up @@ -42,7 +43,7 @@ func TestFouDeserializeMsg(t *testing.T) {
}

// deserialize truncated attribute header
msg = []byte{3, 1, 0, 0, 5, 0, 2, 0, 2, 0, 0}
msg = []byte{3, 1, 0, 0, 5, 0, 2, 0, 2, 0}
if _, err := deserializeFouMsg(msg); err == nil {
t.Error("expected attribute body truncated error")
} else if err != ErrAttrBodyTruncated {
Expand Down
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