smb3: Avoid Mid pending list corruption

When reconnect happens Mid queue can be corrupted when both
demultiplex and offload thread try to dequeue the MID from the
pending list.

These patches address a problem found during decryption offload:
         CIFS: VFS: trying to dequeue a deleted mid
that could cause a refcount use after free:
         Workqueue: smb3decryptd smb2_decrypt_offload [cifs]

Signed-off-by: Rohith Surabattula <rohiths@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
CC: Stable <stable@vger.kernel.org> #5.4+
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -264,7 +264,7 @@ smb2_revert_current_mid(struct TCP_Server_Info *server, const unsigned int val)
 }
 
 static struct mid_q_entry *
-smb2_find_mid(struct TCP_Server_Info *server, char *buf)
+__smb2_find_mid(struct TCP_Server_Info *server, char *buf, bool dequeue)
 {
 	struct mid_q_entry *mid;
 	struct smb2_sync_hdr *shdr = (struct smb2_sync_hdr *)buf;
@@ -281,6 +281,10 @@ smb2_find_mid(struct TCP_Server_Info *server, char *buf)
 		    (mid->mid_state == MID_REQUEST_SUBMITTED) &&
 		    (mid->command == shdr->Command)) {
 			kref_get(&mid->refcount);
+			if (dequeue) {
+				list_del_init(&mid->qhead);
+				mid->mid_flags |= MID_DELETED;
+			}
 			spin_unlock(&GlobalMid_Lock);
 			return mid;
 		}
@@ -289,6 +293,18 @@ smb2_find_mid(struct TCP_Server_Info *server, char *buf)
 	return NULL;
 }
 
+static struct mid_q_entry *
+smb2_find_mid(struct TCP_Server_Info *server, char *buf)
+{
+	return __smb2_find_mid(server, buf, false);
+}
+
+static struct mid_q_entry *
+smb2_find_dequeue_mid(struct TCP_Server_Info *server, char *buf)
+{
+	return __smb2_find_mid(server, buf, true);
+}
+
 static void
 smb2_dump_detail(void *buf, struct TCP_Server_Info *server)
 {
@@ -4404,7 +4420,10 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 		cifs_dbg(FYI, "%s: server returned error %d\n",
 			 __func__, rdata->result);
 		/* normal error on read response */
-		dequeue_mid(mid, false);
+		if (is_offloaded)
+			mid->mid_state = MID_RESPONSE_RECEIVED;
+		else
+			dequeue_mid(mid, false);
 		return 0;
 	}
 
@@ -4428,7 +4447,10 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 		cifs_dbg(FYI, "%s: data offset (%u) beyond end of smallbuf\n",
 			 __func__, data_offset);
 		rdata->result = -EIO;
-		dequeue_mid(mid, rdata->result);
+		if (is_offloaded)
+			mid->mid_state = MID_RESPONSE_MALFORMED;
+		else
+			dequeue_mid(mid, rdata->result);
 		return 0;
 	}
 
@@ -4444,21 +4466,30 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 			cifs_dbg(FYI, "%s: data offset (%u) beyond 1st page of response\n",
 				 __func__, data_offset);
 			rdata->result = -EIO;
-			dequeue_mid(mid, rdata->result);
+			if (is_offloaded)
+				mid->mid_state = MID_RESPONSE_MALFORMED;
+			else
+				dequeue_mid(mid, rdata->result);
 			return 0;
 		}
 
 		if (data_len > page_data_size - pad_len) {
 			/* data_len is corrupt -- discard frame */
 			rdata->result = -EIO;
-			dequeue_mid(mid, rdata->result);
+			if (is_offloaded)
+				mid->mid_state = MID_RESPONSE_MALFORMED;
+			else
+				dequeue_mid(mid, rdata->result);
 			return 0;
 		}
 
 		rdata->result = init_read_bvec(pages, npages, page_data_size,
 					       cur_off, &bvec);
 		if (rdata->result != 0) {
-			dequeue_mid(mid, rdata->result);
+			if (is_offloaded)
+				mid->mid_state = MID_RESPONSE_MALFORMED;
+			else
+				dequeue_mid(mid, rdata->result);
 			return 0;
 		}
 
@@ -4473,7 +4504,10 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 		/* read response payload cannot be in both buf and pages */
 		WARN_ONCE(1, "buf can not contain only a part of read data");
 		rdata->result = -EIO;
-		dequeue_mid(mid, rdata->result);
+		if (is_offloaded)
+			mid->mid_state = MID_RESPONSE_MALFORMED;
+		else
+			dequeue_mid(mid, rdata->result);
 		return 0;
 	}
 
@@ -4484,7 +4518,10 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 	if (length < 0)
 		return length;
 
-	dequeue_mid(mid, false);
+	if (is_offloaded)
+		mid->mid_state = MID_RESPONSE_RECEIVED;
+	else
+		dequeue_mid(mid, false);
 	return length;
 }
 
@@ -4513,7 +4550,7 @@ static void smb2_decrypt_offload(struct work_struct *work)
 	}
 
 	dw->server->lstrp = jiffies;
-	mid = smb2_find_mid(dw->server, dw->buf);
+	mid = smb2_find_dequeue_mid(dw->server, dw->buf);
 	if (mid == NULL)
 		cifs_dbg(FYI, "mid not found\n");
 	else {