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Fix unmarshal bugs #409

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merged 6 commits into from
Jul 5, 2024
Merged

Fix unmarshal bugs #409

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09755bd
[evm precompiles] do *not* ignore `unmarshal` return value
Vindaar Jun 28, 2024
abddc2b
[io_limbs] handle `unmarshal` for sources longer, but smaller
Vindaar Jun 28, 2024
a1ae4fe
[tests] explicitly pass output size for EVM precompiles, chk exp err
Vindaar Jul 3, 2024
91b2fbb
revert checking of "upper" bytes in `io_limbs.nim`
Vindaar Jul 3, 2024
5d085d2
[evm precompiles] return invalid input size for MSM input.len == 0
Vindaar Jul 3, 2024
51d64b5
[evm precompiles] split parsing of field coords by curve
Vindaar Jul 3, 2024
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3 changes: 2 additions & 1 deletion constantine/ethereum_evm_precompiles.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,8 @@ func parseRawUint[Name: static Algebra](
## Return false if the integer is larger than the field modulus.
## Returns true on success.
var big {.noInit.}: Fp[Name].getBigInt()
big.unmarshal(src, bigEndian)
if not big.unmarshal(src, bigEndian):
return cttEVM_IntLargerThanModulus # `dst` too small for `src`!

if not bool(big < Fp[Name].getModulus()):
return cttEVM_IntLargerThanModulus
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26 changes: 22 additions & 4 deletions constantine/serialization/io_limbs.nim
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Expand Up @@ -63,8 +63,17 @@ func unmarshalLE[T](

# if full, dump
if acc_len >= wordBitWidth:
if dst_idx == dst.len:
return false
if dst_idx == dst.len: # return, however check if all remaining
# elements are 0 (more significant bits beyond `src_idx`)
# For example, given a
# `src = "DDCCBBAA0000"`
# and a 4 byte LittleEndian `BigInt`, `src` is fine, because the most
# significant two bytes are all zero.
var allZero = true
for jidx in src_idx ..< dst.len:
if src[jidx] != 0: allZero = false
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I'll have to review more in-depth that case but we can't leak the position of non-zero bytes as this breaks constant-time property.
And even leaking if something is zero is tricky.

if allZero: return true
else: return false

dst[dst_idx] = acc
inc dst_idx
Expand Down Expand Up @@ -118,8 +127,17 @@ func unmarshalBE[T](

# if full, dump
if acc_len >= wordBitWidth:
if dst_idx == dst.len:
return false
if dst_idx == dst.len: # return, however check if all remaining
# elements are 0 (more significant bits beyond `src_idx-1`)
# For examplle, given a
# `src = "0000AABBCCDD"`
# and a 4 byte BigEndian `BigInt`, `src` is fine, because the most
# significant two bytes are all zero.
var allZero = true
for jidx in countdown(src_idx, 0):
if src[jidx] != 0: allZero = false
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same remark, analyzing the data itself instead of metadata (length) breaks constant-time.

if allZero: return true
else: return false

dst[dst_idx] = acc
inc dst_idx
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