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For our specified use cases, this should help in preventing honest mistakes of users of the contract. I may invoke transferFrom(A, B, Z) and be the owner of Z, but if A is not my correct address, the code will reduce someone else's zombieCount and also emit a Transfer event that's not accurate in what it says.
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👍 I noticed this bug as well while completing the lesson. |
BrandonNoad
reviewed
Jan 2, 2022
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| function transferFrom(address _from, address _to, uint256 _tokenId) external payable { | ||
| require (zombieToOwner[_tokenId] == msg.sender || zombieApprovals[_tokenId] == msg.sender); | ||
| require ((zombieToOwner[_tokenId] == msg.sender && _from == msg.sender) || (zombieApprovals[_tokenId] == msg.sender && _to == msg.sender)); |
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I think in both cases you need to check zombieToOwner[_tokenId] == _from.
So the fix would be:
require (zombieToOwner[_tokenId] == _from && (msg.sender == _from || (msg.sender == _to && zombieApprovals[_tokenId] == msg.sender)));
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I noticed this also and came to see if it was discussed. I think the best place to verify the ownership is in the _transfer function, that way developers don't have to remember to check before calling it: |
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For our specified use cases, this should help in preventing honest mistakes of users of the contract.
I may invoke transferFrom(A, B, Z) and be the owner of Z, but if A is not my correct address, the code will reduce someone else's zombieCount and also emit a Transfer event that's not accurate in what it says.