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fix(policy): reject non-canonical TCB date in policy v2 compare #937

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fix(policy): reject non-canonical TCB date in policy v2 compare #937

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39 changes: 37 additions & 2 deletions src/policy/src/v2/policy.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -607,6 +607,35 @@ struct PolicyProperty {
pub reference: Reference,
}

/// Returns true only for a canonical, fixed-width ISO-8601 UTC timestamp of the
/// exact form "YYYY-MM-DDTHH:MM:SSZ" (e.g. "2025-01-01T00:00:00Z"). Lexicographic
/// ordering of date strings is only valid under this canonical form, so callers
/// that compare dates with `>=` must reject anything else.
fn is_canonical_iso8601(s: &str) -> bool {
let b = s.as_bytes();
if b.len() != 20 {
return false;
}
let is_digit = |i: usize| b[i].is_ascii_digit();
(0..4).all(is_digit)
&& b[4] == b'-'
&& is_digit(5)
&& is_digit(6)
&& b[7] == b'-'
&& is_digit(8)
&& is_digit(9)
&& b[10] == b'T'
&& is_digit(11)
&& is_digit(12)
&& b[13] == b':'
&& is_digit(14)
&& is_digit(15)
&& b[16] == b':'
&& is_digit(17)
&& is_digit(18)
&& b[19] == b'Z'
}

impl PolicyProperty {
pub fn evaluate_integer(
&self,
Expand Down Expand Up @@ -718,8 +747,14 @@ impl PolicyProperty {
match self.operation.as_str() {
"equal" => Ok(value == reference_value),
"greater-or-equal" => {
// Simple lexicographical comparison works for ISO-8601 format (e.g. "2025-01-01T00:00:00Z")
// This is because ISO-8601 is designed to be sortable as strings
// The lexicographical comparison below is only correct when both
// operands are canonical, fixed-width ISO-8601 timestamps (e.g.
// "2025-01-01T00:00:00Z"). A non-canonical value such as "2024-9-1"
// would sort incorrectly (byte '9' > '1'), so reject anything that is
// not in the canonical form before comparing, failing closed.
if !is_canonical_iso8601(value) || !is_canonical_iso8601(reference_value) {
return Err(PolicyError::InvalidReference);
}
Ok(value >= reference_value)
}
_ => Err(PolicyError::InvalidOperation),
Expand Down
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