[PATCH] fs: nfsd: Fix three possible null-pointer dereferences

[Jia-Ju Bai]

In nfs4_xdr_dec_cb_recall(), nfs4_xdr_dec_cb_layout() and
nfs4_xdr_dec_cb_notify_lock(), there is an if statement to check whether
cb is NULL.

When cb is NULL, the three functions all call:
    decode_cb_op_status(..., &cb->cb_status);

Thus, possible null-pointer dereferences may occur.

To fix these possible bugs, -EINVAL is returned when cb is NULL.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
 fs/nfsd/nfs4callback.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index 397eb7820929..55949a158b6b 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -516,7 +516,8 @@ static int nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp,
 		status = decode_cb_sequence4res(xdr, cb);
 		if (unlikely(status || cb->cb_seq_status))
 			return status;
-	}
+	} else
+		return -EINVAL;
 
 	return decode_cb_op_status(xdr, OP_CB_RECALL, &cb->cb_status);
 }
@@ -608,7 +609,9 @@ static int nfs4_xdr_dec_cb_layout(struct rpc_rqst *rqstp,
 		status = decode_cb_sequence4res(xdr, cb);
 		if (unlikely(status || cb->cb_seq_status))
 			return status;
-	}
+	} else
+		return -EINVAL;
+
 	return decode_cb_op_status(xdr, OP_CB_LAYOUTRECALL, &cb->cb_status);
 }
 #endif /* CONFIG_NFSD_PNFS */
@@ -667,7 +670,9 @@ static int nfs4_xdr_dec_cb_notify_lock(struct rpc_rqst *rqstp,
 		status = decode_cb_sequence4res(xdr, cb);
 		if (unlikely(status || cb->cb_seq_status))
 			return status;
-	}
+	} else
+		return -EINVAL;
+	
 	return decode_cb_op_status(xdr, OP_CB_NOTIFY_LOCK, &cb->cb_status);
 }
 
-- 
2.17.0