LibIPC+LibC: Add and use a helper to encode/decoder container sizes

While refactoring the IPC encoders and decoders for fallibility, the
inconsistency in which we transfer container sizes was a frequent thing
to trip over. We currently transfer sizes as any of i32, u32, and u64.
This adds a helper to transfer sizes in one consistent way.

Two special cases here are DeprecatedString and Vector, whose encoding
is depended upon by netdb, so that is also updated here.

Userland/Libraries/LibC/netdb.cpp

@@ -122,20 +122,19 @@ hostent* gethostbyname(char const* name)
         close(fd);
     });
 
-    size_t unsigned_name_length = strlen(name);
+    auto name_length = strlen(name);
-    VERIFY(unsigned_name_length <= NumericLimits<i32>::max());
+    VERIFY(name_length <= NumericLimits<i32>::max());
-    i32 name_length = static_cast<i32>(unsigned_name_length);
 
     struct [[gnu::packed]] {
         u32 message_size;
         u32 endpoint_magic;
         i32 message_id;
-        i32 name_length;
+        u32 name_length;
     } request_header = {
         (u32)(sizeof(request_header) - sizeof(request_header.message_size) + name_length),
         lookup_server_endpoint_magic,
         1,
-        name_length,
+        static_cast<u32>(name_length),
     };
     if (auto nsent = write(fd, &request_header, sizeof(request_header)); nsent < 0) {
         h_errno = TRY_AGAIN;
@@ -148,7 +147,7 @@ hostent* gethostbyname(char const* name)
     if (auto nsent = write(fd, name, name_length); nsent < 0) {
         h_errno = TRY_AGAIN;
         return nullptr;
-    } else if (nsent != name_length) {
+    } else if (static_cast<size_t>(nsent) != name_length) {
         h_errno = NO_RECOVERY;
         return nullptr;
     }
@@ -158,7 +157,7 @@ hostent* gethostbyname(char const* name)
         u32 endpoint_magic;
         i32 message_id;
         i32 code;
-        u64 addresses_count;
+        u32 addresses_count;
     } response_header;
 
     if (auto nreceived = read(fd, &response_header, sizeof(response_header)); nreceived < 0) {
@@ -270,7 +269,7 @@ hostent* gethostbyaddr(void const* addr, socklen_t addr_size, int type)
         u32 endpoint_magic;
         i32 message_id;
         i32 code;
-        i32 name_length;
+        u32 name_length;
     } response_header;
 
     if (auto nreceived = read(fd, &response_header, sizeof(response_header)); nreceived < 0) {
@@ -293,7 +292,7 @@ hostent* gethostbyaddr(void const* addr, socklen_t addr_size, int type)
     if (auto nreceived = read(fd, buffer, response_header.name_length); nreceived < 0) {
         h_errno = TRY_AGAIN;
         return nullptr;
-    } else if (nreceived != response_header.name_length) {
+    } else if (static_cast<u32>(nreceived) != response_header.name_length) {
         h_errno = NO_RECOVERY;
         return nullptr;
     }

Userland/Libraries/LibIPC/Decoder.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <AK/JsonValue.h>
+#include <AK/NumericLimits.h>
 #include <AK/URL.h>
 #include <LibCore/AnonymousBuffer.h>
 #include <LibCore/DateTime.h>
@@ -16,19 +17,24 @@
 
 namespace IPC {
 
+ErrorOr<size_t> Decoder::decode_size()
+{
+    return static_cast<size_t>(TRY(decode<u32>()));
+}
+
 template<>
 ErrorOr<DeprecatedString> decode(Decoder& decoder)
 {
-    auto length = TRY(decoder.decode<i32>());
+    auto length = TRY(decoder.decode_size());
-    if (length < 0)
+    if (length == NumericLimits<u32>::max())
         return DeprecatedString {};
     if (length == 0)
         return DeprecatedString::empty();
 
     char* text_buffer = nullptr;
-    auto text_impl = StringImpl::create_uninitialized(static_cast<size_t>(length), text_buffer);
+    auto text_impl = StringImpl::create_uninitialized(length, text_buffer);
 
-    Bytes bytes { text_buffer, static_cast<size_t>(length) };
+    Bytes bytes { text_buffer, length };
     TRY(decoder.decode_into(bytes));
 
     return DeprecatedString { *text_impl };
@@ -37,8 +43,8 @@ ErrorOr<DeprecatedString> decode(Decoder& decoder)
 template<>
 ErrorOr<ByteBuffer> decode(Decoder& decoder)
 {
-    auto length = TRY(decoder.decode<i32>());
+    auto length = TRY(decoder.decode_size());
-    if (length <= 0)
+    if (length == 0)
         return ByteBuffer {};
 
     auto buffer = TRY(ByteBuffer::create_uninitialized(length));
@@ -65,10 +71,7 @@ ErrorOr<URL> decode(Decoder& decoder)
 template<>
 ErrorOr<Dictionary> decode(Decoder& decoder)
 {
-    auto size = TRY(decoder.decode<u64>());
+    auto size = TRY(decoder.decode_size());
-    if (size >= NumericLimits<i32>::max())
-        VERIFY_NOT_REACHED();
-
     Dictionary dictionary {};
 
     for (size_t i = 0; i < size; ++i) {
@@ -99,7 +102,7 @@ ErrorOr<Core::AnonymousBuffer> decode(Decoder& decoder)
     if (auto valid = TRY(decoder.decode<bool>()); !valid)
         return Core::AnonymousBuffer {};
 
-    auto size = TRY(decoder.decode<u32>());
+    auto size = TRY(decoder.decode_size());
     auto anon_file = TRY(decoder.decode<IPC::File>());
 
     return Core::AnonymousBuffer::create_from_anon_fd(anon_file.take_fd(), size);

Userland/Libraries/LibIPC/Decoder.h

@@ -50,6 +50,8 @@ public:
         return {};
     }
 
+    ErrorOr<size_t> decode_size();
+
     Core::Stream::LocalSocket& socket() { return m_socket; }
 
 private:
@@ -96,11 +98,9 @@ ErrorOr<Empty> decode(Decoder&);
 template<Concepts::Vector T>
 ErrorOr<T> decode(Decoder& decoder)
 {
-    auto size = TRY(decoder.decode<u64>());
-    if (size > NumericLimits<i32>::max())
-        return Error::from_string_literal("IPC: Invalid Vector size");
-
     T vector;
+
+    auto size = TRY(decoder.decode_size());
     TRY(vector.try_ensure_capacity(size));
 
     for (size_t i = 0; i < size; ++i) {
@@ -114,12 +114,11 @@ ErrorOr<T> decode(Decoder& decoder)
 template<Concepts::HashMap T>
 ErrorOr<T> decode(Decoder& decoder)
 {
-    auto size = TRY(decoder.decode<u32>());
-    if (size > NumericLimits<i32>::max())
-        return Error::from_string_literal("IPC: Invalid HashMap size");
-
     T hashmap;
 
+    auto size = TRY(decoder.decode_size());
+    TRY(hashmap.try_ensure_capacity(size));
+
     for (size_t i = 0; i < size; ++i) {
         auto key = TRY(decoder.decode<typename T::KeyType>());
         auto value = TRY(decoder.decode<typename T::ValueType>());

Userland/Libraries/LibIPC/Encoder.cpp

@@ -10,6 +10,7 @@
 #include <AK/DeprecatedString.h>
 #include <AK/JsonObject.h>
 #include <AK/JsonValue.h>
+#include <AK/NumericLimits.h>
 #include <AK/URL.h>
 #include <LibCore/AnonymousBuffer.h>
 #include <LibCore/DateTime.h>
@@ -21,6 +22,13 @@
 
 namespace IPC {
 
+ErrorOr<void> Encoder::encode_size(size_t size)
+{
+    if (static_cast<u64>(size) > static_cast<u64>(NumericLimits<u32>::max()))
+        return Error::from_string_literal("Container exceeds the maximum allowed size");
+    return encode(static_cast<u32>(size));
+}
+
 template<>
 ErrorOr<void> encode(Encoder& encoder, float const& value)
 {
@@ -43,10 +51,11 @@ ErrorOr<void> encode(Encoder& encoder, StringView const& value)
 template<>
 ErrorOr<void> encode(Encoder& encoder, DeprecatedString const& value)
 {
+    // NOTE: Do not change this encoding without also updating LibC/netdb.cpp.
     if (value.is_null())
-        return encoder.encode(-1);
+        return encoder.encode(NumericLimits<u32>::max());
 
-    TRY(encoder.encode(static_cast<i32>(value.length())));
+    TRY(encoder.encode_size(value.length()));
     TRY(encoder.encode(value.view()));
     return {};
 }
@@ -54,7 +63,7 @@ ErrorOr<void> encode(Encoder& encoder, DeprecatedString const& value)
 template<>
 ErrorOr<void> encode(Encoder& encoder, ByteBuffer const& value)
 {
-    TRY(encoder.encode(static_cast<i32>(value.size())));
+    TRY(encoder.encode_size(value.size()));
     TRY(encoder.append(value.data(), value.size()));
     return {};
 }
@@ -74,7 +83,7 @@ ErrorOr<void> encode(Encoder& encoder, URL const& value)
 template<>
 ErrorOr<void> encode(Encoder& encoder, Dictionary const& dictionary)
 {
-    TRY(encoder.encode(static_cast<u64>(dictionary.size())));
+    TRY(encoder.encode_size(dictionary.size()));
 
     TRY(dictionary.try_for_each_entry([&](auto const& key, auto const& value) -> ErrorOr<void> {
         TRY(encoder.encode(key));
@@ -109,7 +118,7 @@ ErrorOr<void> encode(Encoder& encoder, Core::AnonymousBuffer const& buffer)
     TRY(encoder.encode(buffer.is_valid()));
 
     if (buffer.is_valid()) {
-        TRY(encoder.encode(static_cast<u32>(buffer.size())));
+        TRY(encoder.encode_size(buffer.size()));
         TRY(encoder.encode(IPC::File { buffer.fd() }));
     }
 

Userland/Libraries/LibIPC/Encoder.h

@@ -57,6 +57,8 @@ public:
         return m_buffer.fds.try_append(move(auto_fd));
     }
 
+    ErrorOr<void> encode_size(size_t size);
+
 private:
     void encode_u32(u32);
     void encode_u64(u64);
@@ -134,7 +136,8 @@ ErrorOr<void> encode(Encoder&, Empty const&);
 template<Concepts::Vector T>
 ErrorOr<void> encode(Encoder& encoder, T const& vector)
 {
-    TRY(encoder.encode(static_cast<u64>(vector.size())));
+    // NOTE: Do not change this encoding without also updating LibC/netdb.cpp.
+    TRY(encoder.encode_size(vector.size()));
 
     for (auto const& value : vector)
         TRY(encoder.encode(value));
@@ -145,7 +148,7 @@ ErrorOr<void> encode(Encoder& encoder, T const& vector)
 template<Concepts::HashMap T>
 ErrorOr<void> encode(Encoder& encoder, T const& hashmap)
 {
-    TRY(encoder.encode(static_cast<u32>(hashmap.size())));
+    TRY(encoder.encode_size(hashmap.size()));
 
     for (auto it : hashmap) {
         TRY(encoder.encode(it.key));