cifs: Fix potential softlockups while refreshing DFS cache

We used to skip reconnects on all SMB2_IOCTL commands due to SMB3+
FSCTL_VALIDATE_NEGOTIATE_INFO - which made sense since we're still
establishing a SMB session.

However, when refresh_cache_worker() calls smb2_get_dfs_refer() and
we're under reconnect, SMB2_ioctl() will not be able to get a proper
status error (e.g. -EHOSTDOWN in case we failed to reconnect) but an
-EAGAIN from cifs_send_recv() thus looping forever in
refresh_cache_worker().

Fixes: e99c63e4d8 ("SMB3: Fix deadlock in validate negotiate hits reconnect")
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Suggested-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -252,7 +252,7 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon)
 	if (tcon == NULL)
 		return 0;
 
-	if (smb2_command == SMB2_TREE_CONNECT || smb2_command == SMB2_IOCTL)
+	if (smb2_command == SMB2_TREE_CONNECT)
 		return 0;
 
 	if (tcon->tidStatus == CifsExiting) {
@@ -426,16 +426,9 @@ fill_small_buf(__le16 smb2_command, struct cifs_tcon *tcon, void *buf,
  * SMB information in the SMB header. If the return code is zero, this
  * function must have filled in request_buf pointer.
  */
-static int
-smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
-		    void **request_buf, unsigned int *total_len)
+static int __smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
+				  void **request_buf, unsigned int *total_len)
 {
-	int rc;
-
-	rc = smb2_reconnect(smb2_command, tcon);
-	if (rc)
-		return rc;
-
 	/* BB eventually switch this to SMB2 specific small buf size */
 	if (smb2_command == SMB2_SET_INFO)
 		*request_buf = cifs_buf_get();
@@ -456,7 +449,31 @@ smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
 		cifs_stats_inc(&tcon->num_smbs_sent);
 	}
 
-	return rc;
+	return 0;
+}
+
+static int smb2_plain_req_init(__le16 smb2_command, struct cifs_tcon *tcon,
+			       void **request_buf, unsigned int *total_len)
+{
+	int rc;
+
+	rc = smb2_reconnect(smb2_command, tcon);
+	if (rc)
+		return rc;
+
+	return __smb2_plain_req_init(smb2_command, tcon, request_buf,
+				     total_len);
+}
+
+static int smb2_ioctl_req_init(u32 opcode, struct cifs_tcon *tcon,
+			       void **request_buf, unsigned int *total_len)
+{
+	/* Skip reconnect only for FSCTL_VALIDATE_NEGOTIATE_INFO IOCTLs */
+	if (opcode == FSCTL_VALIDATE_NEGOTIATE_INFO) {
+		return __smb2_plain_req_init(SMB2_IOCTL, tcon, request_buf,
+					     total_len);
+	}
+	return smb2_plain_req_init(SMB2_IOCTL, tcon, request_buf, total_len);
 }
 
 /* For explanation of negotiate contexts see MS-SMB2 section 2.2.3.1 */
@@ -2686,7 +2703,7 @@ SMB2_ioctl_init(struct cifs_tcon *tcon, struct smb_rqst *rqst,
 	int rc;
 	char *in_data_buf;
 
-	rc = smb2_plain_req_init(SMB2_IOCTL, tcon, (void **) &req, &total_len);
+	rc = smb2_ioctl_req_init(opcode, tcon, (void **) &req, &total_len);
 	if (rc)
 		return rc;