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net: dns: Check compression flag properly

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Allow only 0xc (0b11) as two highest bit to mark the compression
when parsing the CNAME response. See RFC 9267 ch. 2 for details.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
This commit is contained in:
Jukka Rissanen 2025-03-27 14:19:46 +02:00 committed by Benjamin Cabé
parent b086c9d0f0
commit 137eba4e40
1 changed files with 5 additions and 2 deletions
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7
subsys/net/lib/dns/dns_pack.c
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@ -386,7 +386,7 @@ int dns_copy_qname(uint8_t *buf, uint16_t *len, uint16_t size,
lb_size = msg[pos];
/* pointer */
if (lb_size > DNS_LABEL_MAX_SIZE) {
if ((lb_size & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
uint8_t mask = DNS_LABEL_MAX_SIZE;
if (pos + 1 >= msg_size) {
@ -409,6 +409,9 @@ int dns_copy_qname(uint8_t *buf, uint16_t *len, uint16_t size,
}
continue;
} else if (lb_size & NS_CMPRSFLGS) {
rc = -EINVAL;
break;
}
/* validate that the label (i.e. size + elements),
@ -498,7 +501,7 @@ static int dns_unpack_name(const uint8_t *msg, int maxlen, const uint8_t *src,
}
while ((val = *curr_src++)) {
if (val & NS_CMPRSFLGS) {
if ((val & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
/* Follow pointer */
int pos;