[PATCH 4.11 073/114] cifs: fix CIFS_ENUMERATE_SNAPSHOTS oops

[Greg Kroah-Hartman]

4.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Disseldorp <ddiss@xxxxxxx>

commit 6026685de33b0db5b2b6b0e9b41b3a1a3261033c upstream.

As with 618763958b22, an open directory may have a NULL private_data
pointer prior to readdir. CIFS_ENUMERATE_SNAPSHOTS must check for this
before dereference.

Fixes: 834170c85978 ("Enable previous version support")
Signed-off-by: David Disseldorp <ddiss@xxxxxxx>
Signed-off-by: Steve French <smfrench@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/cifs/ioctl.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/cifs/ioctl.c
+++ b/fs/cifs/ioctl.c
@@ -213,6 +213,8 @@ long cifs_ioctl(struct file *filep, unsi
 			rc = smb_mnt_get_fsinfo(xid, tcon, (void __user *)arg);
 			break;
 		case CIFS_ENUMERATE_SNAPSHOTS:
+			if (pSMBFile == NULL)
+				break;
 			if (arg == 0) {
 				rc = -EINVAL;
 				goto cifs_ioc_exit;