container: Validate binary eACL input in setEACL method

Previously `setEACL` method could throw `invalid offset` fault exception
about invalid eACL argument. This message is too generic, may occur in
different places of execution code and doesn't help caller to realize
the reason. To improve user experience, it's worth to check method
arguments before slice instructions.

Pre-check `eACL` slice length in `SetEACL` method implementation and
throw responsive panic message.

Ref nspcc-dev#329.

Signed-off-by: Leonard Lyubich <[email protected]>

container/container_contract.go

@@ -477,8 +477,15 @@ func SetEACL(eACL []byte, signature interop.Signature, publicKey interop.PublicK
 
 	// V2 format
 	// get container ID
+	lnEACL := len(eACL)
+	if lnEACL < 2 {
+		panic("missing version field in eACL BLOB")
+	}
 	offset := int(eACL[1])
 	offset = 2 + offset + 4
+	if lnEACL < offset+containerIDSize {
+		panic("missing container ID field in eACL BLOB")
+	}
 	containerID := eACL[offset : offset+containerIDSize]
 
 	ownerID := getOwnerByID(ctx, containerID)

tests/container_test.go

@@ -336,6 +336,33 @@ func TestContainerSetEACL(t *testing.T) {
 		stackitem.NewByteArray(e.token),
 	})
 	c.Invoke(t, expected, "eACL", cnt.id[:])
+
+	replaceEACLArg := func(eACL []byte) []interface{} {
+		res := make([]interface{}, len(setArgs))
+		copy(res, setArgs)
+		res[0] = eACL
+		return res
+	}
+
+	checkInvalidEACL := func(eACL []byte, exception string) {
+		c.InvokeFail(t, exception, "setEACL", replaceEACLArg(eACL)...)
+	}
+
+	const missingVersionException = "missing version field in eACL BLOB"
+	const missingContainerException = "missing container ID field in eACL BLOB"
+
+	checkInvalidEACL([]byte{}, missingVersionException)
+	checkInvalidEACL([]byte{0}, missingVersionException)
+	checkInvalidEACL([]byte{0, 0, 0}, missingContainerException)
+
+	const offset = byte(20) // any
+
+	// first byte can be any since protobuf is not completely decoded
+	prefix := append([]byte{0, offset}, make([]byte, offset+4)...)
+
+	checkInvalidEACL(prefix, missingContainerException)
+	checkInvalidEACL(append(prefix, make([]byte, len(cnt.id)-1)...), missingContainerException)
+	c.Invoke(t, stackitem.Null{}, "setEACL", replaceEACLArg(append(prefix, cnt.id[:]...))...)
 }
 
 func TestContainerSizeEstimation(t *testing.T) {