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dhcp, ndp, dhcpv6: Support for multiple DNS servers, search list

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Add support for a variable amount of DNS servers, including zero,
from /etc/resolv.conf, in DHCP, NDP and DHCPv6 implementations.

Introduce support for domain search list for DHCP (RFC 3397),
NDP (RFC 8106), and DHCPv6 (RFC 3646), also sourced from
/etc/resolv.conf.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2021-05-21 11:14:47 +02:00
parent 0231ac1c86
commit 9010054ea4
6 changed files with 312 additions and 45 deletions

97
dhcp.c
View file

@ -45,7 +45,6 @@ struct opt {
static struct opt opts[255] = {
[1] = { 0, 4, { 0 }, 0, { 0 }, }, /* Mask */
[3] = { 0, 4, { 0 }, 0, { 0 }, }, /* Router */
[6] = { 0, 4, { 0 }, 0, { 0 }, }, /* DNS */
[51] = { 0, 4, { 0xff, 0xff, 0xff, 0xff }, 0, { 0 }, }, /* Lease time */
[53] = { 0, 1, { 0 }, 0, { 0 }, }, /* Type */
#define DHCPDISCOVER 1
@ -154,6 +153,92 @@ static int fill(struct msg *m)
return offset;
}
/**
* opt_dns_search_dup_ptr() - Look for possible domain name compression pointer
* @buf: Current option buffer with existing labels
* @cmp: Portion of domain name being added
* @len: Length of current option buffer
*
* Return: offset to corresponding compression pointer if any, -1 if not found
*/
static int opt_dns_search_dup_ptr(unsigned char *buf, char *cmp, size_t len)
{
unsigned int i;
for (i = 0; i < len; i++) {
if (buf[i] == 0 &&
len - i - 1 >= strlen(cmp) &&
!memcmp(buf + i + 1, cmp, strlen(cmp)))
return i;
if ((buf[i] & 0xc0) == 0xc0 &&
len - i - 2 >= strlen(cmp) &&
!memcmp(buf + i + 2, cmp, strlen(cmp)))
return i + 1;
}
return -1;
}
/**
* opt_set_dns_search() - Fill data and set length for Domain Search option
* @c: Execution context
* @max_len: Maximum total length of option buffer
*/
static void opt_set_dns_search(struct ctx *c, size_t max_len)
{
char buf[NS_MAXDNAME];
int i;
opts[119].slen = 0;
for (i = 0; i < 255; i++)
max_len -= opts[i].slen;
for (i = 0; *c->dns_search[i].n; i++) {
unsigned int n;
int dup = -1;
char *p;
buf[0] = 0;
for (p = c->dns_search[i].n, n = 1; *p; p++) {
if (*p == '.') {
/* RFC 1035 4.1.4 Message compression */
dup = opt_dns_search_dup_ptr(opts[119].s, p + 1,
opts[119].slen);
if (dup >= 0) {
buf[n++] = '\xc0';
buf[n++] = dup;
break;
} else {
buf[n++] = '.';
}
} else {
buf[n++] = *p;
}
}
/* The compression pointer is also an end of label */
if (dup < 0)
buf[n++] = 0;
if (n >= max_len)
break;
memcpy(opts[119].s + opts[119].slen, buf, n);
opts[119].slen += n;
max_len -= n;
}
for (i = 0; i < opts[119].slen; i++) {
if (!opts[119].s[i] || opts[119].s[i] == '.') {
opts[119].s[i] = strcspn((char *)opts[119].s + i + 1,
".\xc0");
}
}
}
/**
* dhcp() - Check if this is a DHCP message, reply as needed
* @c: Execution context
@ -213,10 +298,16 @@ int dhcp(struct ctx *c, struct ethhdr *eh, size_t len)
m->yiaddr = c->addr4;
*(unsigned long *)opts[1].s = c->mask4;
*(unsigned long *)opts[3].s = c->gw4;
*(unsigned long *)opts[6].s = c->dns4;
*(unsigned long *)opts[54].s = c->gw4;
uh->len = htons(len = offsetof(struct msg, o) + fill(m));
for (i = 0, opts[6].slen = 0; c->dns4[i]; i++) {
((uint32_t *)opts[6].s)[i] = c->dns4[i];
opts[6].slen += sizeof(uint32_t);
}
opt_set_dns_search(c, sizeof(m->o));
uh->len = htons(len = offsetof(struct msg, o) + fill(m) + sizeof(*uh));
uh->check = 0;
uh->source = htons(67);
uh->dest = htons(68);