hare

commit b3ee22310122a141475760fd30e77190785a614b
parent c2f6ac88a7e113bed7c260c4286453936148fd1e
Author: Conrad Hoffmann <ch@bitfehler.net>
Date:   Mon,  7 Aug 2023 16:37:44 +0200

net::dns: enforce actual label size restriction

The length of a label is indicated by a one byte value, but the upper
two bits are reserved for the "compression" algorithm (aka pointers).
See RFC 1035 section 4.1.4 [1] or the decoding functions, where pointers
are already implemented.

While at it, return an error instead of asserting.

[1] https://datatracker.ietf.org/doc/html/rfc1035#section-4.1.4

Signed-off-by: Conrad Hoffmann <ch@bitfehler.net>

Diffstat:
M
net/dns/encode.ha
 | 
5
+++--

1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/dns/encode.ha b/net/dns/encode.ha
@@ -71,8 +71,9 @@ fn encode_raw(enc: *encoder, val: []u8) (void | error) = {
 fn encode_labels(enc: *encoder, names: []str) (void | error) = {
 	// TODO: Assert that the labels are all valid ASCII?
 	for (let i = 0z; i < len(names); i += 1) {
-		// XXX: Should I return an error instead of asserting?
-		assert(len(names[i]) < 256);
+		if (len(names[i]) > 63) {
+			return format;
+		};
 		if (len(enc.buf) <= enc.offs + 1 + len(names[i])) {
 			return errors::overflow;
 		};