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resolved: tweak how we calculate MTU for sending packets

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Let's take all MTU info we possibly have into account, i.e. the one
reported via netlink, as before and the one the socket might now (from
PMTUD and such), clamped by our own ideas.
This commit is contained in:
Lennart Poettering
2021-02-18 15:55:58 +01:00
parent 4565863fff
commit d79677ab44
4 changed files with 59 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/resolve/resolved-dns-scope.c
+56 -26
View File
@@ -5,6 +5,7 @@
#include "af-list.h"
#include "alloc-util.h"
#include "dns-domain.h"
#include "errno-util.h"
#include "fd-util.h"
#include "hostname-util.h"
#include "missing_network.h"
@@ -185,43 +186,73 @@ void dns_scope_packet_lost(DnsScope *s, usec_t usec) {
s->resend_timeout = MIN(s->resend_timeout * 2, MULTICAST_RESEND_TIMEOUT_MAX_USEC);
}
static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
union in_addr_union addr;
int ifindex = 0, r;
int family;
uint32_t mtu;
static int dns_scope_emit_one(DnsScope *s, int fd, int family, DnsPacket *p) {
int r;
assert(s);
assert(p);
assert(p->protocol == s->protocol);
if (s->link) {
mtu = s->link->mtu;
ifindex = s->link->ifindex;
} else
mtu = manager_find_mtu(s->manager);
if (family == AF_UNSPEC) {
if (s->family == AF_UNSPEC)
return -EAFNOSUPPORT;
family = s->family;
}
switch (s->protocol) {
case DNS_PROTOCOL_DNS:
case DNS_PROTOCOL_DNS: {
size_t mtu, udp_size, min_mtu, socket_mtu = 0;
assert(fd >= 0);
if (DNS_PACKET_QDCOUNT(p) > 1)
if (DNS_PACKET_QDCOUNT(p) > 1) /* Classic DNS only allows one question per packet */
return -EOPNOTSUPP;
if (p->size > DNS_PACKET_UNICAST_SIZE_MAX)
return -EMSGSIZE;
if (p->size + UDP4_PACKET_HEADER_SIZE > mtu)
return -EMSGSIZE;
/* Determine the local most accurate MTU */
if (s->link)
mtu = s->link->mtu;
else
mtu = manager_find_mtu(s->manager);
/* Acquire the socket's PMDU MTU */
r = socket_get_mtu(fd, family, &socket_mtu);
if (r < 0 && !ERRNO_IS_DISCONNECT(r)) /* Will return ENOTCONN if no information is available yet */
return log_debug_errno(r, "Failed to read socket MTU: %m");
/* Determine the appropriate UDP header size */
udp_size = udp_header_size(family);
min_mtu = udp_size + DNS_PACKET_HEADER_SIZE;
log_debug("Emitting UDP, link MTU is %zu, socket MTU is %zu, minimal MTU is %zu",
mtu, socket_mtu, min_mtu);
/* Clamp by the kernel's idea of the (path) MTU */
if (socket_mtu != 0 && socket_mtu < mtu)
mtu = socket_mtu;
/* Put a lower limit, in case all MTU data we acquired was rubbish */
if (mtu < min_mtu)
mtu = min_mtu;
/* Now check our packet size against the MTU we determined */
if (udp_size + p->size > mtu)
return -EMSGSIZE; /* This means: try TCP instead */
r = manager_write(s->manager, fd, p);
if (r < 0)
return r;
break;
}
case DNS_PROTOCOL_LLMNR: {
union in_addr_union addr;
case DNS_PROTOCOL_LLMNR:
assert(fd < 0);
if (DNS_PACKET_QDCOUNT(p) > 1)
@@ -230,8 +261,6 @@ static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
if (!ratelimit_below(&s->ratelimit))
return -EBUSY;
family = s->family;
if (family == AF_INET) {
addr.in = LLMNR_MULTICAST_IPV4_ADDRESS;
fd = manager_llmnr_ipv4_udp_fd(s->manager);
@@ -243,20 +272,20 @@ static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
if (fd < 0)
return fd;
r = manager_send(s->manager, fd, ifindex, family, &addr, LLMNR_PORT, NULL, p);
r = manager_send(s->manager, fd, s->link->ifindex, family, &addr, LLMNR_PORT, NULL, p);
if (r < 0)
return r;
break;
}
case DNS_PROTOCOL_MDNS:
case DNS_PROTOCOL_MDNS: {
union in_addr_union addr;
assert(fd < 0);
if (!ratelimit_below(&s->ratelimit))
return -EBUSY;
family = s->family;
if (family == AF_INET) {
addr.in = MDNS_MULTICAST_IPV4_ADDRESS;
fd = manager_mdns_ipv4_fd(s->manager);
@@ -268,11 +297,12 @@ static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
if (fd < 0)
return fd;
r = manager_send(s->manager, fd, ifindex, family, &addr, MDNS_PORT, NULL, p);
r = manager_send(s->manager, fd, s->link->ifindex, family, &addr, MDNS_PORT, NULL, p);
if (r < 0)
return r;
break;
}
default:
return -EAFNOSUPPORT;
@@ -281,7 +311,7 @@ static int dns_scope_emit_one(DnsScope *s, int fd, DnsPacket *p) {
return 1;
}
int dns_scope_emit_udp(DnsScope *s, int fd, DnsPacket *p) {
int dns_scope_emit_udp(DnsScope *s, int fd, int af, DnsPacket *p) {
int r;
assert(s);
@@ -296,7 +326,7 @@ int dns_scope_emit_udp(DnsScope *s, int fd, DnsPacket *p) {
dns_packet_set_flags(p, true, true);
}
r = dns_scope_emit_one(s, fd, p);
r = dns_scope_emit_one(s, fd, af, p);
if (r < 0)
return r;
@@ -1133,7 +1163,7 @@ static int on_conflict_dispatch(sd_event_source *es, usec_t usec, void *userdata
return 0;
}
r = dns_scope_emit_udp(scope, -1, p);
r = dns_scope_emit_udp(scope, -1, AF_UNSPEC, p);
if (r < 0)
log_debug_errno(r, "Failed to send conflict packet: %m");
}
@@ -1430,7 +1460,7 @@ int dns_scope_announce(DnsScope *scope, bool goodbye) {
if (r < 0)
return log_debug_errno(r, "Failed to build reply packet: %m");
r = dns_scope_emit_udp(scope, -1, p);
r = dns_scope_emit_udp(scope, -1, AF_UNSPEC, p);
if (r < 0)
return log_debug_errno(r, "Failed to send reply packet: %m");
src/resolve/resolved-dns-scope.h
+1 -1
View File
@@ -71,7 +71,7 @@ DnsScope* dns_scope_free(DnsScope *s);
void dns_scope_packet_received(DnsScope *s, usec_t rtt);
void dns_scope_packet_lost(DnsScope *s, usec_t usec);
int dns_scope_emit_udp(DnsScope *s, int fd, DnsPacket *p);
int dns_scope_emit_udp(DnsScope *s, int fd, int af, DnsPacket *p);
int dns_scope_socket_tcp(DnsScope *s, int family, const union in_addr_union *address, DnsServer *server, uint16_t port, union sockaddr_union *ret_socket_address);
int dns_scope_socket_udp(DnsScope *s, DnsServer *server);
src/resolve/resolved-dns-transaction.c
+1 -1
View File
@@ -1470,7 +1470,7 @@ static int dns_transaction_emit_udp(DnsTransaction *t) {
} else
dns_transaction_close_connection(t, true);
r = dns_scope_emit_udp(t->scope, t->dns_udp_fd, t->sent);
r = dns_scope_emit_udp(t->scope, t->dns_udp_fd, t->server ? t->server->family : AF_UNSPEC, t->sent);
if (r < 0)
return r;
src/resolve/resolved-mdns.c
+1 -1
View File
@@ -237,7 +237,7 @@ static int mdns_scope_process_query(DnsScope *s, DnsPacket *p) {
if (!ratelimit_below(&s->ratelimit))
return 0;
r = dns_scope_emit_udp(s, -1, reply);
r = dns_scope_emit_udp(s, -1, AF_UNSPEC, reply);
if (r < 0)
return log_debug_errno(r, "Failed to send reply packet: %m");