leb128: avoid shifts larger than type (#123)

2022-07-16 19:16:11 +02:00 · 2022-07-16 19:16:11 +02:00 · 9a3130eb5b
parent b55c5a6d74
commit 9a3130eb5b
1 changed files with 5 additions and 0 deletions
--- a/stew/leb128.nim
+++ b/stew/leb128.nim
@ -109,6 +109,11 @@ template read7(shift: untyped) =
  if (shift div 7) >= xlen:
    return (I(0), 0'i8) # Not enough data - return 0 bytes read

+  when shift >= sizeof(I) * 8:
+    # avoid shift overflows: https://github.com/nim-lang/Nim/issues/19983
+    if true:
+      return (I(0), -cast[int8]((shift div 7) + 1))
+
  let
    b = x[shift div 7]
    valb = b and 0x7f'u8 # byte without high bit