ksmbd: don't allow O_TRUNC open on read-only share

When file is changed using notepad on read-only share(read_only = yes in
ksmbd.conf), There is a problem where existing data is truncated.
notepad in windows try to O_TRUNC open(FILE_OVERWRITE_IF) and all data
in file is truncated. This patch don't allow  O_TRUNC open on read-only
share and add KSMBD_TREE_CONN_FLAG_WRITABLE check in smb2_set_info().

Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/smb2pdu.c

@@ -2972,7 +2972,7 @@ int smb2_open(struct ksmbd_work *work)
 					    &may_flags);
 
 	if (!test_tree_conn_flag(tcon, KSMBD_TREE_CONN_FLAG_WRITABLE)) {
-		if (open_flags & O_CREAT) {
+		if (open_flags & (O_CREAT | O_TRUNC)) {
 			ksmbd_debug(SMB,
 				    "User does not have write permission\n");
 			rc = -EACCES;
@@ -5944,12 +5944,6 @@ static int smb2_set_info_file(struct ksmbd_work *work, struct ksmbd_file *fp,
 	}
 	case FILE_RENAME_INFORMATION:
 	{
-		if (!test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE)) {
-			ksmbd_debug(SMB,
-				    "User does not have write permission\n");
-			return -EACCES;
-		}
-
 		if (buf_len < sizeof(struct smb2_file_rename_info))
 			return -EINVAL;
 
@@ -5969,12 +5963,6 @@ static int smb2_set_info_file(struct ksmbd_work *work, struct ksmbd_file *fp,
 	}
 	case FILE_DISPOSITION_INFORMATION:
 	{
-		if (!test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE)) {
-			ksmbd_debug(SMB,
-				    "User does not have write permission\n");
-			return -EACCES;
-		}
-
 		if (buf_len < sizeof(struct smb2_file_disposition_info))
 			return -EINVAL;
 
@@ -6036,7 +6024,7 @@ int smb2_set_info(struct ksmbd_work *work)
 {
 	struct smb2_set_info_req *req;
 	struct smb2_set_info_rsp *rsp;
-	struct ksmbd_file *fp;
+	struct ksmbd_file *fp = NULL;
 	int rc = 0;
 	unsigned int id = KSMBD_NO_FID, pid = KSMBD_NO_FID;
 
@@ -6056,6 +6044,13 @@ int smb2_set_info(struct ksmbd_work *work)
 		rsp = smb2_get_msg(work->response_buf);
 	}
 
+	if (!test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE)) {
+		ksmbd_debug(SMB, "User does not have write permission\n");
+		pr_err("User does not have write permission\n");
+		rc = -EACCES;
+		goto err_out;
+	}
+
 	if (!has_file_id(id)) {
 		id = req->VolatileFileId;
 		pid = req->PersistentFileId;