[PATCH 4.19 076/313] nfsd4: fix crash on writing v4_end_grace before nfsd startup

From: Greg Kroah-Hartman
Date: Mon Feb 11 2019 - 09:41:56 EST

4.19-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 <anatoly.trosinenko@xxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
fs/nfsd/nfsctl.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 7fb9f7c667b1..899174c7a8ae 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;