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From:   "NeilBrown" <neilb@suse.de>
To:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     Linux NFS list <linux-nfs@vger.kernel.org>,
        Olga Kornievskaia <kolga@netapp.com>,
        Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>
Subject: [PATCH] NFSD: fix possible oops when nfsd/pool_stats is closed.
Date:   Tue, 12 Sep 2023 11:25:00 +1000
Message-id: <169448190063.19905.9707641304438290692@noble.neil.brown.name>
Precedence: bulk


If /proc/fs/nfsd/pool_stats is open when the last nfsd thread exits, then
when the file is closed a NULL pointer is dereferenced.
This is because nfsd_pool_stats_release() assumes that the
pointer to the svc_serv cannot become NULL while a reference is held.

This used to be the case but a recent patch split nfsd_last_thread() out
from nfsd_put(), and clearing the pointer is done in nfsd_last_thread().

This is easily reproduced by running
   rpc.nfsd 8 ; ( rpc.nfsd 0;true) < /proc/fs/nfsd/pool_stats

Fortunately nfsd_pool_stats_release() has easy access to the svc_serv
pointer, and so can call svc_put() on it directly.

Fixes: 9f28a971ee9f ("nfsd: separate nfsd_last_thread() from nfsd_put()")
Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/nfsd/nfssvc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 1582af33e204..551c16a72012 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -1082,11 +1082,12 @@ int nfsd_pool_stats_open(struct inode *inode, struct =
file *file)
=20
 int nfsd_pool_stats_release(struct inode *inode, struct file *file)
 {
+	struct svc_serv *serv =3D
+		((struct seq_file *) file->private_data)->private;
 	int ret =3D seq_release(inode, file);
-	struct net *net =3D inode->i_sb->s_fs_info;
=20
 	mutex_lock(&nfsd_mutex);
-	nfsd_put(net);
+	svc_put(serv);
 	mutex_unlock(&nfsd_mutex);
 	return ret;
 }
--=20
2.42.0