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Date:   Mon, 11 Feb 2019 15:15:16 +0100
From:   Greg Kroah-Hartman <>
Cc:     Greg Kroah-Hartman <>,,
        Anatoly Trosinenko <>,
        "J. Bruce Fields" <>,
        Sasha Levin <>
Subject: [PATCH 4.20 089/352] nfsd4: fix crash on writing v4_end_grace before nfsd startup

4.20-stable review patch.  If anyone has any objections, please let me know.


[ Upstream commit 62a063b8e7d1db684db3f207261a466fa3194e72 ]

Anatoly Trosinenko reports that this:

1) Checkout fresh master Linux branch (tested with commit e195ca6cb)
2) Copy x84_64-config-4.14 to .config, then enable NFS server v4 and build
3) From `kvm-xfstests shell`:

results in NULL dereference in locks_end_grace.

Check that nfsd has been started before trying to end the grace period.

Reported-by: Anatoly Trosinenko <>
Signed-off-by: J. Bruce Fields <>
Signed-off-by: Sasha Levin <>
 fs/nfsd/nfsctl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 6384c9b94898..b33f9785b756 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1126,6 +1126,8 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size)
 		case 'Y':
 		case 'y':
 		case '1':
+			if (nn->nfsd_serv)
+				return -EBUSY;

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