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Kernel: Don't cast to NetworkOrdered<u16>* from random data

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NetworkOrdered is a non trivial type, and it's undefined behavior to
cast a random pointer to it and then pretend it's that type.

Instead just call AK::convert_between_host_and_network_endian on the
individual u16*. This suppresses static analysis warnings.

I don't think there was a "bug" in the previous code, it worked, but
it was very brittle.
This commit is contained in:
Brian Gianforcaro 2021-09-01 00:27:42 -07:00 committed by Andreas Kling
parent 668c429900
commit afa0fb55b0
Notes: sideshowbarker 2024-07-18 04:56:20 +09:00 
Author: https://github.com/bgianfo
Commit: https://github.com/SerenityOS/serenity/commit/afa0fb55b01
Pull-request: https://github.com/SerenityOS/serenity/pull/9720
1 changed files with 6 additions and 6 deletions
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12
Kernel/Net/TCPSocket.cpp
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@ -338,22 +338,22 @@ NetworkOrdered<u16> TCPSocket::compute_tcp_checksum(const IPv4Address& source, c
PseudoHeader pseudo_header { source, destination, 0, (u8)IPv4Protocol::TCP, packet.header_size() + payload_size };
u32 checksum = 0;
auto* w = (const NetworkOrdered<u16>*)&pseudo_header;
auto raw_pseudo_header = bit_cast<u16*>(&pseudo_header);
for (size_t i = 0; i < sizeof(pseudo_header) / sizeof(u16); ++i) {
checksum += w[i];
checksum += AK::convert_between_host_and_network_endian(raw_pseudo_header[i]);
if (checksum > 0xffff)
checksum = (checksum >> 16) + (checksum & 0xffff);
}
w = (const NetworkOrdered<u16>*)&packet;
auto raw_packet = bit_cast<u16*>(&packet);
for (size_t i = 0; i < packet.header_size() / sizeof(u16); ++i) {
checksum += w[i];
checksum += AK::convert_between_host_and_network_endian(raw_packet[i]);
if (checksum > 0xffff)
checksum = (checksum >> 16) + (checksum & 0xffff);
}
VERIFY(packet.data_offset() * 4 == packet.header_size());
w = (const NetworkOrdered<u16>*)packet.payload();
auto raw_payload = bit_cast<u16*>(packet.payload());
for (size_t i = 0; i < payload_size / sizeof(u16); ++i) {
checksum += w[i];
checksum += AK::convert_between_host_and_network_endian(raw_payload[i]);
if (checksum > 0xffff)
checksum = (checksum >> 16) + (checksum & 0xffff);
}