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Fix: doublehashes can use different hashes #28

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merged 2 commits into from
Oct 27, 2023
Merged

Fix: doublehashes can use different hashes #28

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a8ac7a7
Fix: doublehashes can use different hashes
hsanjuan Oct 23, 2023
25d9833
Make sure double-hashes are detected and blocked correctly
hsanjuan Oct 25, 2023
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15 changes: 8 additions & 7 deletions denylist.go
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Original file line number Diff line number Diff line change
Expand Up @@ -371,18 +371,19 @@ func (dl *Denylist) parseLine(line string, number uint64) error {
// It can be a Multihash (CIDv0) or a sha256-hex-encoded string.

var mhType uint64
// attempt to parse CID
// attempt to parse a b58btc-encoded multihash
rule = strings.TrimPrefix(rule, "//")
c, err := cid.Decode(rule)
mh, err := multihash.FromB58String(rule)
if err == nil {
prefix := c.Prefix()
if prefix.Version != 0 {
return fmt.Errorf("double-hash is not a raw-multihash (cidv0) (%s:%d)", dl.Filename, number)
dmh, err := multihash.Decode(mh)
if err != nil {
return fmt.Errorf("what appears to be a multihash b58 string cannot be decoded (%s:%d): %w", dl.Filename, number, err)
}
e.Multihash = c.Hash()

e.Multihash = mh
// we use the multihash codec to group double-hashes
// with the same hashing function.
mhType = c.Prefix().MhType
mhType = dmh.Code
} else { // Assume a hex-encoded sha256 string
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@lidel there is a problem here...

some of the badbits hex-encoded strings parse just fine as B58 strings, resulting in valid multihashes with weird code, which then make the whole error checking break for anything later.

I assume the other way around also is an issue: some b58 strings could perhaps be hex-decoded... ? If you have thoughts, they are welcome.

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Creating two rules sgtm.

bs, err := hex.DecodeString(rule)
if err != nil {
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3 changes: 2 additions & 1 deletion tester/test.deny
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Expand Up @@ -78,4 +78,5 @@ author: "@hsanjuan"
# (different codec)
# And /ipfs/f01701e20903cf61d46521b05f926ba1634628d0bba8a7ffb5b6d5a3ca310682ca63b5ef0/path
# But not /path2
//QmbK7LDv5NNBvYQzNfm2eED17SNLt1yNMapcUhSuNLgkqz
//gW813G35CnLsy7gRYYHuf63hrz71U1xoLFDVeV7actx6oX