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fix(lwip): reject invalid DHCP MTU option values

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Validate MTU from DHCP option 26 against RFC 2132 minimum (68 bytes)
before applying to netif->mtu, preventing rogue DHCP servers from
setting MTU to 0 or other dangerously low values that cause integer
wraparound in IPv4 fragmentation.
This commit is contained in:
David Cermak
2026-06-18 12:59:56 +02:00
parent 6fa5704eda
commit d45d04dc43
1 changed files with 3 additions and 0 deletions
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3
components/lwip/port/hooks/lwip_default_hooks.c
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@@ -234,6 +234,9 @@ void dhcp_parse_extra_opts(struct dhcp *dhcp, uint8_t state, uint8_t option, uin
NETIF_FOREACH(netif) {
/* find the netif related to this dhcp */
if (dhcp == netif_dhcp_data(netif)) {
if (mtu < 68) { /* RFC 2132 requires MTU >= 68 */
return;
}
if (mtu < netif->mtu) {
netif->mtu = mtu;
LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_parse_extra_opts(): Negotiated netif MTU is %d\n", netif->mtu));