zircon/system/ulib/fidl/validating.cpp

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/fidl/coding.h>

#include <stdalign.h>
#include <stdint.h>
#include <stdlib.h>

#include <lib/fidl/envelope_frames.h>
#include <lib/fidl/internal.h>
#include <lib/fidl/visitor.h>
#include <lib/fidl/walker.h>
#include <zircon/assert.h>
#include <zircon/compiler.h>

// TODO(kulakowski) Design zx_status_t error values.

namespace {

struct Position;

struct StartingPoint {
    const uint8_t* const addr;
    Position ToPosition() const;
};

struct Position {
    uint32_t offset;
    Position operator+(uint32_t size) const {
        return Position{offset + size};
    }
    Position& operator+=(uint32_t size) {
        offset += size;
        return *this;
    }
    template <typename T>
    constexpr const T* Get(StartingPoint start) const {
        return reinterpret_cast<const T*>(start.addr + offset);
    }
};

Position StartingPoint::ToPosition() const {
    return Position{0};
}

constexpr uintptr_t kAllocPresenceMarker = FIDL_ALLOC_PRESENT;
constexpr uintptr_t kAllocAbsenceMarker = FIDL_ALLOC_ABSENT;

using EnvelopeState = ::fidl::EnvelopeFrames::EnvelopeState;

class FidlValidator final : public fidl::Visitor<
                                fidl::NonMutatingVisitorTrait, StartingPoint, Position> {
public:
    FidlValidator(uint32_t num_bytes, uint32_t num_handles, uint32_t next_out_of_line,
                  const char** out_error_msg)
        : num_bytes_(num_bytes), num_handles_(num_handles), next_out_of_line_(next_out_of_line),
          out_error_msg_(out_error_msg) {}

    using StartingPoint = StartingPoint;

    using Position = Position;

    static constexpr bool kContinueAfterConstraintViolation = true;

    Status VisitPointer(Position ptr_position,
                        ObjectPointerPointer object_ptr_ptr,
                        uint32_t inline_size,
                        Position* out_position) {
        if (reinterpret_cast<uintptr_t>(*object_ptr_ptr) != kAllocPresenceMarker) {
            SetError("validator encountered invalid pointer");
            return Status::kConstraintViolationError;
        }
        uint32_t new_offset;
        if (!fidl::AddOutOfLine(next_out_of_line_, inline_size, &new_offset)) {
            SetError("overflow updating out-of-line offset");
            return Status::kMemoryError;
        }
        if (new_offset > num_bytes_) {
            SetError("message tried to access more than provided number of bytes");
            return Status::kMemoryError;
        }
        // TODO(FIDL-237): Check the padding gaps are zero.
        *out_position = Position{next_out_of_line_};
        next_out_of_line_ = new_offset;
        return Status::kSuccess;
    }

    Status VisitHandle(Position handle_position, HandlePointer handle) {
        if (*handle != FIDL_HANDLE_PRESENT) {
            SetError("message contains a garbage handle");
            return Status::kConstraintViolationError;
        }
        if (handle_idx_ == num_handles_) {
            SetError("message has too many handles");
            return Status::kConstraintViolationError;
        }
        handle_idx_++;
        return Status::kSuccess;
    }

    Status VisitInternalPadding(Position padding_position, uint32_t padding_length) {
        // TODO(FIDL-237): Turn this on after prebuilts have picked up new encoder.
        // auto padding_ptr = padding_position.template Get<const uint8_t>(StartingPoint{bytes_});
        // for (uint32_t i = 0; i < padding_length; i++) {
        //     if (padding_ptr[i] != 0) {
        //         SetError("non-zero padding bytes detected");
        //         return Status::kConstraintViolationError;
        //     }
        // }
        return Status::kSuccess;
    }

    Status EnterEnvelope(Position envelope_position,
                         EnvelopePointer envelope,
                         const fidl_type_t* payload_type) {
        if (envelope->presence == kAllocAbsenceMarker &&
            (envelope->num_bytes != 0 || envelope->num_handles != 0)) {
            SetError("Envelope has absent data pointer, yet has data and/or handles");
            return Status::kConstraintViolationError;
        }
        if (envelope->presence != kAllocAbsenceMarker && envelope->num_bytes == 0) {
            SetError("Envelope has present data pointer, but zero byte count");
            return Status::kConstraintViolationError;
        }
        uint32_t expected_handle_count;
        if (add_overflow(handle_idx_, envelope->num_handles, &expected_handle_count) ||
            expected_handle_count > num_handles_) {
            SetError("Envelope has more handles than expected");
            return Status::kConstraintViolationError;
        }
        // Remember the current watermark of bytes and handles, so that after processing
        // the envelope, we can validate that the claimed num_bytes/num_handles matches the reality.
        if (!envelope_frames_.Push(EnvelopeState(next_out_of_line_, handle_idx_))) {
            SetError("Overly deep nested envelopes");
            return Status::kConstraintViolationError;
        }
        // If we do not have the coding table for this payload,
        // treat it as unknown and add its contained handles
        if (envelope->presence != kAllocAbsenceMarker && payload_type == nullptr) {
            handle_idx_ += envelope->num_handles;
        }
        return Status::kSuccess;
    }

    Status LeaveEnvelope(Position envelope_position, EnvelopePointer envelope) {
        // Now that the envelope has been consumed, check the correctness of the envelope header.
        auto& starting_state = envelope_frames_.Pop();
        uint32_t num_bytes = next_out_of_line_ - starting_state.bytes_so_far;
        uint32_t num_handles = handle_idx_ - starting_state.handles_so_far;
        if (envelope->num_bytes != num_bytes) {
            SetError("Envelope num_bytes was mis-sized");
            return Status::kConstraintViolationError;
        }
        if (envelope->num_handles != num_handles) {
            SetError("Envelope num_handles was mis-sized");
            return Status::kConstraintViolationError;
        }
        return Status::kSuccess;
    }

    void OnError(const char* error) {
        SetError(error);
    }

    zx_status_t status() const { return status_; }

    bool DidConsumeAllBytes() const { return next_out_of_line_ == num_bytes_; }

    bool DidConsumeAllHandles() const { return handle_idx_ == num_handles_; }

private:
    void SetError(const char* error) {
        if (status_ == ZX_OK) {
            status_ = ZX_ERR_INVALID_ARGS;
            if (out_error_msg_ != nullptr) {
                *out_error_msg_ = error;
            }
        }
    }

    // Message state passed in to the constructor.
    const uint32_t num_bytes_;
    const uint32_t num_handles_;
    uint32_t next_out_of_line_;
    const char** const out_error_msg_;

    // Validator state
    zx_status_t status_ = ZX_OK;
    uint32_t handle_idx_ = 0;
    fidl::EnvelopeFrames envelope_frames_;
};

} // namespace

zx_status_t fidl_validate(const fidl_type_t* type, const void* bytes, uint32_t num_bytes,
                          uint32_t num_handles, const char** out_error_msg) {
    auto set_error = [&out_error_msg](const char* msg) {
        if (out_error_msg)
            *out_error_msg = msg;
    };
    if (bytes == nullptr) {
        set_error("Cannot validate null bytes");
        return ZX_ERR_INVALID_ARGS;
    }

    uint32_t next_out_of_line;
    zx_status_t status;
    if ((status = fidl::StartingOutOfLineOffset(type,
                                                num_bytes,
                                                &next_out_of_line,
                                                out_error_msg)) != ZX_OK) {
        return status;
    }

    FidlValidator validator(num_bytes, num_handles, next_out_of_line, out_error_msg);
    fidl::Walk(validator,
               type,
               StartingPoint{reinterpret_cast<const uint8_t*>(bytes)});

    if (validator.status() == ZX_OK) {
        if (!validator.DidConsumeAllBytes()) {
            set_error("message did not consume all provided bytes");
            return ZX_ERR_INVALID_ARGS;
        }
        if (!validator.DidConsumeAllHandles()) {
            set_error("message did not reference all provided handles");
            return ZX_ERR_INVALID_ARGS;
        }
    }

    return validator.status();
}

zx_status_t fidl_validate_msg(const fidl_type_t* type, const fidl_msg_t* msg,
                              const char** out_error_msg) {
    return fidl_validate(type, msg->bytes, msg->num_bytes, msg->num_handles,
                         out_error_msg);
}