All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The transaction you mentioned is forbidden for two reasons:
1- The creditor conditioned the debtor to pay an extra amount over the narrowed sum; this is Riba (interest and/or usury) without doubt. Ibn Qudaamah said: “Any loan in which an increase is conditioned is forbidden without any difference of opinion in this regard.”
2- The creditor conditioned to possess the mortgage if the debtor is unable to repay the loan; this is an invalid condition. Al-Jassaas said regarding conditioning the possession of the mortgage for the person with whom the mortgage is kept when the period of loan ends: “The scholars agreed that the creditor is not permitted to own the mortgage when the period expires, but they differed about whether or not the mortgage is lawful or unlawful.”
The majority of the scholars are of the view that this condition is void and it renders the mortgage contract void. Ibn Qudaamah said: "This is narrated from Ibn 'Umar, Shurayh, An-Naf'i, Maalik, Ath-Thawri, Ash-Shaafi'i, and the Hanafi scholars, and we do not know any scholar who contradicted them."
The evidence about this is the narration which reads: “There should be no conditions in the mortgage.”; meaning a person should not give a mortgage to another person and tell him “If I give you back your money on such and such date, otherwise the mortgage becomes your property.”