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Add reply-push synchronization

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This is used to avoid the server reading incorrect/corrupted reply
contents for pushed replies. This was happening because clients were
sending the push-reply call with the pointer to the message contents,
but they were immediately returning after sending it. This led to a race
condition in which the server would sometimes read the data after the
client had already overwritten/discarded said data.
This commit is contained in:
Ariel Abreu 2022-06-24 01:39:04 -04:00
parent 700d89812c
commit 4f001e2a34
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GPG Key ID: D67AE16CCEA85B70
1 changed files with 14 additions and 1 deletions
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15
src/call.cpp
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@ -133,6 +133,14 @@ std::shared_ptr<DarlingServer::Call> DarlingServer::Call::callFromMessage(Messag
auto pushReplyCall = reinterpret_cast<const dserver_rpc_call_push_reply_t*>(requestMessage.data().data());
Message replyToSave(pushReplyCall->reply_size, 0);
// extract the reply-push synchronization pipe
auto pipeDesc = requestMessage.extractDescriptorAtIndex(requestMessage.descriptors().size() - 1);
char tmp = 1;
if (pipeDesc < 0) {
throw std::runtime_error("Failed to extract reply-push synchronization pipe");
}
if (!process->readMemory(pushReplyCall->reply, replyToSave.data().data(), pushReplyCall->reply_size)) {
throw std::runtime_error("Failed to read client-pushed reply body");
}
@ -160,7 +168,12 @@ std::shared_ptr<DarlingServer::Call> DarlingServer::Call::callFromMessage(Messag
}
}
callLog.debug() << *thread << ": Saved client-pushed reply" << callLog.endLog;
callLog.debug() << *thread << ": Saved client-pushed reply (" << ((thread->_pendingSavedReply) ? "pending" : "normal") << ")" << callLog.endLog;
// write a byte to the pipe so the caller can continue
write(pipeDesc, &tmp, sizeof(tmp));
// and close it
close(pipeDesc);
return nullptr;
}