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authorStefano Brivio <sbrivio@redhat.com>2022-11-08 08:31:59 +0100
committerStefano Brivio <sbrivio@redhat.com>2022-11-10 11:17:50 +0100
commit510dace86ccf0bd63be3b1dbd35ae9c0b0538e5b (patch)
treed4f8a673d811a82cc71dc11f0c2c2521cf566065 /udp.c
parente308018bbe2a42a9ad9af5302fe855eee508acc2 (diff)
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tap: Keep stream consistent if qemu length descriptor spans two recv() calls
I got all paranoid after triggering a divide-by-zero general protection fault in passt with a qemu version without the virtio_net TX hang fix, while flooding UDP. I start thinking this was actually coming from some random changes I was playing with, but before reaching this conclusion I reviewed once more the relatively short path in tap_handler_passt() before we start using packet_*() functions, and found this. Never observed in practice, but artificially reproduced with changes in qemu's socket interface: if we don't receive from qemu a complete length descriptor in one recv() call, or if we receive a partial one at the end of one call, we currently disregard the rest, which would make the stream inconsistent. Nothing really bad happens, except that from that point on we would disregard all the packets we get until, if ever, we get the stream back in sync by chance. Force reading a complete packet length descriptor with a blocking recv(), if needed -- not just a complete packet later. Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
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