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From:   Jeff Layton <jlayton@kernel.org>
To:     chuck.lever@oracle.com
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH] nfsd: fix potential race in nfs4_find_file
Date:   Thu,  5 Jan 2023 07:18:23 -0500
Message-Id: <20230105121823.21935-1-jlayton@kernel.org>
MIME-Version: 1.0
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Even though there is a WARN_ON_ONCE check, it seems possible for
nfs4_find_file to race with the destruction of an fi_deleg_file while
trying to take a reference to it.

put_deleg_file is done while holding the fi_lock. Take and hold it
when dealing with the fi_deleg_file in nfs4_find_file.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfs4state.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index b68238024e49..3df3ae84bd07 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6417,23 +6417,27 @@ nfsd4_lookup_stateid(struct nfsd4_compound_state *cstate,
 static struct nfsd_file *
 nfs4_find_file(struct nfs4_stid *s, int flags)
 {
+	struct nfsd_file *ret = NULL;
+
 	if (!s)
 		return NULL;
 
 	switch (s->sc_type) {
 	case NFS4_DELEG_STID:
-		if (WARN_ON_ONCE(!s->sc_file->fi_deleg_file))
-			return NULL;
-		return nfsd_file_get(s->sc_file->fi_deleg_file);
+		spin_lock(&s->sc_file->fi_lock);
+		if (!WARN_ON_ONCE(!s->sc_file->fi_deleg_file))
+			ret = nfsd_file_get(s->sc_file->fi_deleg_file);
+		spin_unlock(&s->sc_file->fi_lock);
+		break;
 	case NFS4_OPEN_STID:
 	case NFS4_LOCK_STID:
 		if (flags & RD_STATE)
-			return find_readable_file(s->sc_file);
+			ret = find_readable_file(s->sc_file);
 		else
-			return find_writeable_file(s->sc_file);
+			ret = find_writeable_file(s->sc_file);
 	}
 
-	return NULL;
+	return ret;
 }
 
 static __be32
-- 
2.39.0