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Fix overflow in Message::canonical_name when ancount is u16::MAX #708

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Fix overflow in Message::canonical_name when ancount is u16::MAX #708

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15 changes: 14 additions & 1 deletion src/base/message.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -524,7 +524,7 @@ impl<Octs: Octets + ?Sized> Message<Octs> {
Err(_) => return None,
};

for _ in 0..self.header_counts().ancount() + 1 {
for _ in 0..self.header_counts().ancount().saturating_add(1) {
let mut found = false;
for record in answer.clone() {
let record = match record {
Expand Down Expand Up @@ -1444,6 +1444,19 @@ mod test {
assert!(msg.as_message().canonical_name().is_none());
}

#[test]
#[cfg(feature = "alloc")]
fn canonical_name_max_ancount() {
// Must not panic with arithmetic overflow.
let mut msg = MessageBuilder::new_vec().question();
msg.push((Name::root_vec(), Rtype::A)).unwrap();
let mut buf = msg.finish();
HeaderCounts::for_message_slice_mut(buf.as_mut())
.set_ancount(u16::MAX);
let msg = Message::from_octets(buf.as_slice()).unwrap();
let _ = msg.canonical_name();
}

#[test]
#[cfg(feature = "alloc")]
fn message_iterator() {
Expand Down