Armaan Sandhu
4a25049a9e
manager_recv() sizes its buffer with next_datagram_size_fd(), which peeks at the datagram with MSG_PEEK|MSG_TRUNC. That peek makes the kernel verify the UDP checksum - which is the whole point of using it over FIONREAD - and hence also drop the datagram when the checksum is bad. The datagram that woke the event source can thus be gone by the time we peek at it, and the peek returns EAGAIN. manager_recv() returned that error, while the recvmsg_safe() below, which can fail the same way, already treats it as "no packet". The callers on the mDNS, LLMNR and stub listening sockets pass a negative return on to the event loop, which disables the event source, so a single datagram with a bad checksum - something anyone on the link can send - stops resolved from receiving on that socket for good. on_dns_packet() completes the transaction with -EAGAIN instead of retrying it. So return 0 on a transient error here too, like the other users of the helper on an event source do. Disconnect errors are left as they are: they show up here from ICMP errors on the connected UDP socket, and on_dns_packet() handles them.
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