[PATCH 5.4.y] nfsd: handle get_client_locked() failure in nfsd4_setclientid_confirm()

[Sasha Levin <sashal@kernel.org>]

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit 908e4ead7f757504d8b345452730636e298cbf68 ]

Lei Lu recently reported that nfsd4_setclientid_confirm() did not check
the return value from get_client_locked(). a SETCLIENTID_CONFIRM could
race with a confirmed client expiring and fail to get a reference. That
could later lead to a UAF.

Fix this by getting a reference early in the case where there is an
extant confirmed client. If that fails then treat it as if there were no
confirmed client found at all.

In the case where the unconfirmed client is expiring, just fail and
return the result from get_client_locked().

Reported-by: lei lu <llfamsec@gmail.com>
Closes: https://lore.kernel.org/linux-nfs/CAEBF3_b=UvqzNKdnfD_52L05Mqrqui9vZ2eFamgAbV0WG+FNWQ@mail.gmail.com/
Fixes: d20c11d86d8f ("nfsd: Protect session creation and client confirm using client_lock")
Cc: stable@vger.kernel.org
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
[ Adjust context ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfs4state.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index a3f8660803c7..f915fef7ca6b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -3956,10 +3956,16 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
 	}
 	status = nfs_ok;
 	if (conf) { /* case 1: callback update */
-		old = unconf;
-		unhash_client_locked(old);
-		nfsd4_change_callback(conf, &unconf->cl_cb_conn);
-	} else { /* case 3: normal case; new or rebooted client */
+		if (get_client_locked(conf) == nfs_ok) {
+			old = unconf;
+			unhash_client_locked(old);
+			nfsd4_change_callback(conf, &unconf->cl_cb_conn);
+		} else {
+			conf = NULL;
+		}
+	}
+
+	if (!conf) { /* case 3: normal case; new or rebooted client */
 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
 		if (old) {
 			status = nfserr_clid_inuse;
@@ -3975,10 +3981,14 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
 				goto out;
 			}
 		}
+		status = get_client_locked(unconf);
+		if (status != nfs_ok) {
+			old = NULL;
+			goto out;
+		}
 		move_to_confirmed(unconf);
 		conf = unconf;
 	}
-	get_client_locked(conf);
 	spin_unlock(&nn->client_lock);
 	nfsd4_probe_callback(conf);
 	spin_lock(&nn->client_lock);
-- 
2.50.1