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nfsd: cut the Linux NFSv4.1/4.2 some slack w.r.t. RFC5661

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Recent testing of network partitioning a FreeBSD NFSv4.1
server from a Linux NFSv4.1 client identified problems
with both the FreeBSD server and Linux client.

Sometimes, after some Linux NFSv4.1/4.2 clients establish
a new TCP connection, they will advance the sequence number
for a session slot by 2 instead of 1.
RFC5661 specifies that a server should reply
NFS4ERR_SEQ_MISORDERED for this case.
This might result in a system call error in the client and
seems to disable future use of the slot by the client.
Since advancing the sequence number by 2 seems harmless,
allow this case if vfs.nfs.linuxseqsesshack is non-zero.

Note that, if the order of RPCs is actually reversed,
a subsequent RPC with a smaller sequence number value
for the slot will be received.  This will result in
a NFS4ERR_SEQ_MISORDERED reply.
This has not been observed during testing.
Setting vfs.nfs.linuxseqsesshack to 0 will provide
RFC5661 compliant behaviour.

This fix affects the fairly rare case where a NFSv4
Linux client does a TCP reconnect and then apparently
erroneously increments the sequence number for the
session slot twice during the reconnect cycle.

PR:	254816
MFC after:	2 weeks
This commit is contained in:
Rick Macklem 2021-04-11 16:51:25 -07:00
parent 774cbf9b64
commit 9edaceca81
1 changed files with 20 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
sys/fs/nfs/nfs_commonsubs.c
View File

@ -98,6 +98,11 @@ int nfs_maxcopyrange = 10 * 1024 * 1024;
SYSCTL_INT(_vfs_nfs, OID_AUTO, maxcopyrange, CTLFLAG_RW,
&nfs_maxcopyrange, 0, "Max size of a Copy so RPC times reasonable");
static int nfs_allowskip_sessionseq = 1;
SYSCTL_INT(_vfs_nfs, OID_AUTO, linuxseqsesshack, CTLFLAG_RW,
&nfs_allowskip_sessionseq, 0, "Allow client to skip ahead one seq# for"
" session slot");
/*
* This array of structures indicates, for V4:
* retfh - which of 3 types of calling args are used
@ -4614,7 +4619,7 @@ nfsv4_getipaddr(struct nfsrv_descript *nd, struct sockaddr_in *sin,
* Handle an NFSv4.1 Sequence request for the session.
* If reply != NULL, use it to return the cached reply, as required.
* The client gets a cached reply via this call for callbacks, however the
* server gets a cached reply via the nfsv4_seqsess_cachereply() call.
* server gets a cached reply via the nfsv4_seqsess_cacherep() call.
*/
int
nfsv4_seqsession(uint32_t seqid, uint32_t slotid, uint32_t highslot,
@ -4648,12 +4653,24 @@ nfsv4_seqsession(uint32_t seqid, uint32_t slotid, uint32_t highslot,
} else
/* No reply cached, so just do it. */
slots[slotid].nfssl_inprog = 1;
} else if ((slots[slotid].nfssl_seq + 1) == seqid) {
} else if (slots[slotid].nfssl_seq + 1 == seqid ||
(slots[slotid].nfssl_seq + 2 == seqid &&
nfs_allowskip_sessionseq != 0)) {
/*
* Allowing the seqid to be ahead by 2 is technically
* a violation of RFC5661, but it seems harmless to do
* and avoids returning NFSERR_SEQMISORDERED to a
* slightly broken Linux NFSv4.1/4.2 client.
* If the RPCs are really out of order, one with a
* lower seqid will be subsequently received and that
* one will get a NFSERR_SEQMISORDERED reply.
* Can be disabled by setting vfs.nfs.linuxseqsesshack to 0.
*/
if (slots[slotid].nfssl_reply != NULL)
m_freem(slots[slotid].nfssl_reply);
slots[slotid].nfssl_reply = NULL;
slots[slotid].nfssl_inprog = 1;
slots[slotid].nfssl_seq++;
slots[slotid].nfssl_seq = seqid;
} else
error = NFSERR_SEQMISORDERED;
return (error);