linux-kernel - [PATCH 4.19 076/313] nfsd4: fix crash on writing v4_end

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Message-Id: <20190211141858.952421765@linuxfoundation.org>
Date:   Mon, 11 Feb 2019 15:15:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Anatoly Trosinenko <anatoly.trosinenko@...il.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 076/313] nfsd4: fix crash on writing v4_end_grace before nfsd startup

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@...il.com>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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;
 			nfsd4_end_grace(nn);
 			break;
 		default:
-- 
2.19.1