[PATCH 5.4 062/138] nfsd4: fix NULL dereference in nfsd/clients display code

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: J. Bruce Fields <bfields@xxxxxxxxxx>

[ Upstream commit 9affa435817711861d774f5626c393c80f16d044 ]

We hold the cl_lock here, and that's enough to keep stateid's from going
away, but it's not enough to prevent the files they point to from going
away.  Take fi_lock and a reference and check for NULL, as we do in
other code.

Reported-by: NeilBrown <neilb@xxxxxxx>
Fixes: 78599c42ae3c ("nfsd4: add file to display list of client's opens")
Reviewed-by: NeilBrown <neilb@xxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/nfsd/nfs4state.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 9af9b673f2923..68cf116607645 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -506,6 +506,17 @@ find_any_file(struct nfs4_file *f)
 	return ret;
 }
 
+static struct nfsd_file *find_deleg_file(struct nfs4_file *f)
+{
+	struct nfsd_file *ret = NULL;
+
+	spin_lock(&f->fi_lock);
+	if (f->fi_deleg_file)
+		ret = nfsd_file_get(f->fi_deleg_file);
+	spin_unlock(&f->fi_lock);
+	return ret;
+}
+
 static atomic_long_t num_delegations;
 unsigned long max_delegations;
 
@@ -2378,6 +2389,8 @@ static int nfs4_show_open(struct seq_file *s, struct nfs4_stid *st)
 	oo = ols->st_stateowner;
 	nf = st->sc_file;
 	file = find_any_file(nf);
+	if (!file)
+		return 0;
 
 	seq_printf(s, "- 0x%16phN: { type: open, ", &st->sc_stateid);
 
@@ -2411,6 +2424,8 @@ static int nfs4_show_lock(struct seq_file *s, struct nfs4_stid *st)
 	oo = ols->st_stateowner;
 	nf = st->sc_file;
 	file = find_any_file(nf);
+	if (!file)
+		return 0;
 
 	seq_printf(s, "- 0x%16phN: { type: lock, ", &st->sc_stateid);
 
@@ -2439,7 +2454,9 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)
 
 	ds = delegstateid(st);
 	nf = st->sc_file;
-	file = nf->fi_deleg_file;
+	file = find_deleg_file(nf);
+	if (!file)
+		return 0;
 
 	seq_printf(s, "- 0x%16phN: { type: deleg, ", &st->sc_stateid);
 
@@ -2451,6 +2468,7 @@ static int nfs4_show_deleg(struct seq_file *s, struct nfs4_stid *st)
 
 	nfs4_show_superblock(s, file);
 	seq_printf(s, " }\n");
+	nfsd_file_put(file);
 
 	return 0;
 }
-- 
2.25.1