Date: Wed, 28 Apr 2021 15:41:20 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: freebsd-stable <freebsd-stable@freebsd.org> Cc: Peter Eriksson <pen@lysator.liu.se>, Ryan Moeller <freqlabs@FreeBSD.org>, Garrett Wollman <wollman@hergotha.csail.mit.edu> Subject: wanna solve the Linux NFSv4 client puzzle? Message-ID: <YQXPR0101MB09682E0EEF2995E3FBC20BB8DD409@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM>
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Hi,=0A= =0A= I posted recently that enabling delegations should be avoided at this time,= =0A= especially if your FreeBSD NFS server has Linux client mounts...=0A= =0A= I thought some of you might be curious why, and I thought it would be=0A= more fun if you look for yourselves.=0A= To play the game, you need to download a packet capture:=0A= fetch https://people.freebsd.org/~rmacklem/twoclientdeleg.pcap=0A= and then load it into wireshark.=0A= =0A= 192.168.1.5 - FreeBSD server with all recent patches=0A= 192.168.1.6 - FedoraCore 30 (Linux 5.2 kernel) client=0A= 192.168.1.13 - FreeBSD client=0A= =0A= A few hints buried in RFC5661:=0A= - A fore channel is used for normal client->server RPCs and a back channel= =0A= is used for server->client callback RPCs.=0A= - After a new TCP is created, neither the fore nor back channels=0A= are bound to the connection.=0A= - Bindings channel(s) to a connection is done by BindConnectionToSession.= =0A= but an implicit binding for the fore channel is created when the first RP= C=0A= request with a Sequence operation in it is sent on the new TCP connection= .=0A= - A server->client callback cannot be done until the back channel is bound= =0A= via BindConnectionToServer.=0A= =0A= Ok, so we are ready...=0A= - Look at packet #s 3518->3605.=0A= - What is going on here?=0A= - How long does this take?=0A= --> One more hint. Starting with #3605, things are working again.=0A= There are actually 3 other examples of this in the pack capture.=0A= =0A= Btw, one of the weirdnesses is said to be fixed in Linux 5.3 and the other= =0A= in Linux 5.7, although I have not yet upgraded my kernel and tested this.= =0A= =0A= Have fun with it, rick=0A=
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