From 34b09af4f54e6485e28f138ccad159611a240cc1 Mon Sep 17 00:00:00 2001
From: J. Bruce Fields
Date: Wed, 5 Aug 2020 15:10:11 -0400
Subject: nfsd: fix oops on mixed NFSv4/NFSv3 client access

If an NFSv2/v3 client breaks an NFSv4 client's delegation, it will hit a
NULL dereference in nfsd_breaker_owns_lease().

Easily reproduceable with for example

	mount -overs=4.2 server:/export /mnt/
	sleep 1h </mnt/file &
	mount -overs=3 server:/export /mnt2/
	touch /mnt2/file

Reported-by: Robert Dinse <nanook@eskimo.com>
Fixes: 28df3d1539de50 ("nfsd: clients don't need to break their own delegations")
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=208807
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4state.c | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'fs')

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 81ed8e8bab3f..1ea9bbcc7c24 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4597,6 +4597,8 @@ static bool nfsd_breaker_owns_lease(struct file_lock *fl)
 	if (!i_am_nfsd())
 		return NULL;
 	rqst = kthread_data(current);
+	if (!rqst->rq_lease_breaker)
+		return NULL;
 	clp = *(rqst->rq_lease_breaker);
 	return dl->dl_stid.sc_client == clp;
 }
-- 
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