Uint shift operations: incorrect overflow flags and truncated shift amounts
| Details |
|
| Package |
ruint |
| Version |
1.18.0 |
| URL |
alloy-rs/ruint#603 |
| Date |
2026-07-08 |
| Patched versions |
>=1.20.0 |
Uint::overflowing_shl/overflowing_shr returned false-negative overflow
flags. overflowing_shl missed bits shifted above BITS but within the top
limb (non-limb-aligned widths such as U160), and limbs wholly discarded by
shifts >= 64; overflowing_shr missed wholly discarded low limbs. Shifted
values were correct; only the flag was wrong.
The wrong flag propagates: checked_shl/checked_shr return Some instead
of None, strict_* fail to panic, and saturating_* return a wrapped
value instead of saturating. The incorrect checked_shl result causes
to_base_be (and string formatting) to loop forever on no-alloc builds for
non-limb-aligned widths — a denial of service if formatting is reachable
from untrusted input.
Separately, wrapping_shl/wrapping_shr on 64/128/256-bit types truncated
the shift amount modulo 2^32, so shifts >= 2^32 returned an incorrectly
wrapped value instead of zero; on 32-bit targets the generic path also
truncated 64-bit shift amounts.
Callers using checked or saturating shift semantics on untrusted shift
amounts may compute incorrect results.
See advisory page for additional details.
ruint1.18.0>=1.20.0Uint::overflowing_shl/overflowing_shrreturned false-negative overflowflags.
overflowing_shlmissed bits shifted aboveBITSbut within the toplimb (non-limb-aligned widths such as
U160), and limbs wholly discarded byshifts >= 64;
overflowing_shrmissed wholly discarded low limbs. Shiftedvalues were correct; only the flag was wrong.
The wrong flag propagates:
checked_shl/checked_shrreturnSomeinsteadof
None,strict_*fail to panic, andsaturating_*return a wrappedvalue instead of saturating. The incorrect
checked_shlresult causesto_base_be(and string formatting) to loop forever on no-alloc builds fornon-limb-aligned widths — a denial of service if formatting is reachable
from untrusted input.
Separately,
wrapping_shl/wrapping_shron 64/128/256-bit types truncatedthe shift amount modulo 2^32, so shifts >= 2^32 returned an incorrectly
wrapped value instead of zero; on 32-bit targets the generic path also
truncated 64-bit shift amounts.
Callers using checked or saturating shift semantics on untrusted shift
amounts may compute incorrect results.
See advisory page for additional details.