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Updated comments for ERC20 proxy to clarify how we load the token address from calldata (3.18 from audit)

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This commit is contained in:
Greg Hysen
2018-08-29 12:25:06 -07:00
parent 1c3b2b7141
commit 8c803ab232
2 changed files with 60 additions and 9 deletions
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67
packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol vendored
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@@ -59,15 +59,64 @@ contract ERC20Proxy is
mstore(96, 0)
revert(0, 100)
}
/////// Token contract address ///////
// The token address is found as follows:
// * It is stored at offset 4 in `assetData` contents.
// * This is stored at offset 32 from `assetData`.
// * The offset to `assetData` from Params is stored at offset
// 4 in calldata.
// * The offset of Params in calldata is 4.
// So we read location 4 and add 32 + 4 + 4 to it.
// `transferFrom`.
// The function is marked `external`, so no abi decodeding is done for
// us. Instead, we expect the `calldata` memory to contain the
// following:
//
// | Area | Offset | Length | Contents |
// |----------|--------|---------|-------------------------------------|
// | Header | 0 | 4 | function selector |
// | Params | | 4 * 32 | function parameters: |
// | | 4 | | 1. offset to assetData (*) |
// | | 36 | | 2. from |
// | | 68 | | 3. to |
// | | 100 | | 4. amount |
// | Data | | | assetData: |
// | | 132 | 32 | assetData Length |
// | | 164 | ** | assetData Contents |
//
// (*): offset is computed from start of function parameters, so offset
// by an additional 4 bytes in the calldata.
//
// (**): see table below to compute length of assetData Contents
//
// WARNING: The ABIv2 specification allows additional padding between
// the Params and Data section. This will result in a larger
// offset to assetData.
// Asset data itself is encoded as follows:
//
// | Area | Offset | Length | Contents |
// |----------|--------|---------|-------------------------------------|
// | Header | 0 | 4 | function selector |
// | Params | | 1 * 32 | function parameters: |
// | | 4 | 12 + 20 | 1. token address |
// We construct calldata for the `token.transferFrom` ABI.
// The layout of this calldata is in the table below.
//
// | Area | Offset | Length | Contents |
// |----------|--------|---------|-------------------------------------|
// | Header | 0 | 4 | function selector |
// | Params | | 3 * 32 | function parameters: |
// | | 4 | | 1. from |
// | | 36 | | 2. to |
// | | 68 | | 3. amount |
/////// Read token address from calldata ///////
// * The token address is stored in `assetData`.
//
// * The "offset to assetData" is stored at offset 4 in the calldata (table 1).
// [assetDataOffsetFromParams = calldataload(4)]
//
// * Notes that the "offset to assetData" is relative to the "Params" area of calldata;
// add 4 bytes to account for the length of the "Header" area (table 1).
// [assetDataOffsetFromHeader = assetDataOffsetFromParams + 4]
//
// * The "token address" is offset 32+4=36 bytes into "assetData" (tables 1 & 2).
// [tokenOffset = assetDataOffsetFromHeader + 36 = calldataload(4) + 4 + 36]
let token := calldataload(add(calldataload(4), 40))
/////// Setup Header Area ///////

2
packages/contracts/src/2.0.0/protocol/AssetProxy/ERC721Proxy.sol vendored
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@@ -80,6 +80,8 @@ contract ERC721Proxy is
// (*): offset is computed from start of function parameters, so offset
// by an additional 4 bytes in the calldata.
//
// (**): see table below to compute length of assetData Contents
//
// WARNING: The ABIv2 specification allows additional padding between
// the Params and Data section. This will result in a larger
// offset to assetData.