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Merge pull request from GHSA-9vx6-7xxf-x967

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* add tests for the encode reads dirty data issue

* Fix the encode reads dirty data issue

* add changeset

* trigger the issue without assembly

* rename mock

* gas optimization

* Apply suggestions from code review

Co-authored-by: Ernesto García <ernestognw@gmail.com>

* alternative fix: cheaper

* update comment

* fix lint

---------

Co-authored-by: Ernesto García <ernestognw@gmail.com>
This commit is contained in:
Hadrien Croubois
2024-02-29 17:03:32 +01:00
committed by GitHub
parent 8b4b7b8d04
commit 92224533b1
4 changed files with 51 additions and 9 deletions
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27
contracts/utils/Base64.sol
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@ -58,12 +58,19 @@ library Base64 {
let tablePtr := add(table, 1)
// Prepare result pointer, jump over length
let resultPtr := add(result, 32)
let resultPtr := add(result, 0x20)
let dataPtr := data
let endPtr := add(data, mload(data))
// In some cases, the last iteration will read bytes after the end of the data. We cache the value, and
// set it to zero to make sure no dirty bytes are read in that section.
let afterPtr := add(endPtr, 0x20)
let afterCache := mload(afterPtr)
mstore(afterPtr, 0x00)
// Run over the input, 3 bytes at a time
for {
let dataPtr := data
let endPtr := add(data, mload(data))
} lt(dataPtr, endPtr) {
} {
@ -71,13 +78,12 @@ library Base64 {
dataPtr := add(dataPtr, 3)
let input := mload(dataPtr)
// To write each character, shift the 3 bytes (18 bits) chunk
// To write each character, shift the 3 byte (24 bits) chunk
// 4 times in blocks of 6 bits for each character (18, 12, 6, 0)
// and apply logical AND with 0x3F which is the number of
// the previous character in the ASCII table prior to the Base64 Table
// The result is then added to the table to get the character to write,
// and finally write it in the result pointer but with a left shift
// of 256 (1 byte) - 8 (1 ASCII char) = 248 bits
// and apply logical AND with 0x3F to bitmask the least significant 6 bits.
// Use this as an index into the lookup table, mload an entire word
// so the desired character is in the least significant byte, and
// mstore8 this least significant byte into the result and continue.
mstore8(resultPtr, mload(add(tablePtr, and(shr(18, input), 0x3F))))
resultPtr := add(resultPtr, 1) // Advance
@ -92,6 +98,9 @@ library Base64 {
resultPtr := add(resultPtr, 1) // Advance
}
// Reset the value that was cached
mstore(afterPtr, afterCache)
if withPadding {
// When data `bytes` is not exactly 3 bytes long
// it is padded with `=` characters at the end