[PATCH 5.8 085/255] nfsd: fix oops on mixed NFSv4/NFSv3 client access

[Greg Kroah-Hartman]

From: J. Bruce Fields <bfields@xxxxxxxxxx>

[ Upstream commit 34b09af4f54e6485e28f138ccad159611a240cc1 ]

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@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/nfsd/nfs4state.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index c9056316a0b35..cea682ce8aa12 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;
 }
-- 
2.25.1