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--dhcp-reply-delay option to workaround PXE client bugs.

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Adds option to delay replying to DHCP packets by one or more seconds.
This provides a workaround for a PXE boot firmware implementation
that has a bug causing it to fail if it receives a (proxy) DHCP
reply instantly.

On Linux it looks up the exact receive time of the UDP packet with
the SIOCGSTAMP ioctl to prevent multiple delays if multiple packets
come in around the same time.
This commit is contained in:
Floris Bos
2017-04-09 23:07:13 +01:00
committed by Simon Kelley
parent 60704f5e2e
commit 503c609149
8 changed files with 158 additions and 57 deletions
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101
src/dnsmasq.c
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@@ -1747,29 +1747,15 @@ int icmp_ping(struct in_addr addr)
{
/* Try and get an ICMP echo from a machine. */
/* Note that whilst in the three second wait, we check for
(and service) events on the DNS and TFTP sockets, (so doing that
better not use any resources our caller has in use...)
but we remain deaf to signals or further DHCP packets. */
/* There can be a problem using dnsmasq_time() to end the loop, since
it's not monotonic, and can go backwards if the system clock is
tweaked, leading to the code getting stuck in this loop and
ignoring DHCP requests. To fix this, we check to see if select returned
as a result of a timeout rather than a socket becoming available. We
only allow this to happen as many times as it takes to get to the wait time
in quarter-second chunks. This provides a fallback way to end loop. */
int fd, rc;
int fd;
struct sockaddr_in saddr;
struct {
struct ip ip;
struct icmp icmp;
} packet;
unsigned short id = rand16();
unsigned int i, j, timeout_count;
unsigned int i, j;
int gotreply = 0;
time_t start, now;
#if defined(HAVE_LINUX_NETWORK) || defined (HAVE_SOLARIS_NETWORK)
if ((fd = make_icmp_sock()) == -1)
@@ -1799,14 +1785,46 @@ int icmp_ping(struct in_addr addr)
while (retry_send(sendto(fd, (char *)&packet.icmp, sizeof(struct icmp), 0,
(struct sockaddr *)&saddr, sizeof(saddr))));
for (now = start = dnsmasq_time(), timeout_count = 0;
(difftime(now, start) < (float)PING_WAIT) && (timeout_count < PING_WAIT * 4);)
gotreply = delay_dhcp(dnsmasq_time(), PING_WAIT, fd, addr.s_addr, id);
#if defined(HAVE_LINUX_NETWORK) || defined(HAVE_SOLARIS_NETWORK)
while (retry_send(close(fd)));
#else
opt = 1;
setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt));
#endif
return gotreply;
}
int delay_dhcp(time_t start, int sec, int fd, uint32_t addr, unsigned short id)
{
/* Delay processing DHCP packets for "sec" seconds counting from "start".
If "fd" is not -1 it will stop waiting if an ICMP echo reply is received
from "addr" with ICMP ID "id" and return 1 */
/* Note that whilst waiting, we check for
(and service) events on the DNS and TFTP sockets, (so doing that
better not use any resources our caller has in use...)
but we remain deaf to signals or further DHCP packets. */
/* There can be a problem using dnsmasq_time() to end the loop, since
it's not monotonic, and can go backwards if the system clock is
tweaked, leading to the code getting stuck in this loop and
ignoring DHCP requests. To fix this, we check to see if select returned
as a result of a timeout rather than a socket becoming available. We
only allow this to happen as many times as it takes to get to the wait time
in quarter-second chunks. This provides a fallback way to end loop. */
int rc, timeout_count;
time_t now;
for (now = dnsmasq_time(), timeout_count = 0;
(difftime(now, start) <= (float)sec) && (timeout_count < sec * 4);)
{
struct sockaddr_in faddr;
socklen_t len = sizeof(faddr);
poll_reset();
poll_listen(fd, POLLIN);
if (fd != -1)
poll_listen(fd, POLLIN);
set_dns_listeners(now);
set_log_writer();
@@ -1823,10 +1841,10 @@ int icmp_ping(struct in_addr addr)
timeout_count++;
now = dnsmasq_time();
check_log_writer(0);
check_dns_listeners(now);
#ifdef HAVE_DHCP6
if (daemon->doing_ra && poll_check(daemon->icmp6fd, POLLIN))
icmp6_packet(now);
@@ -1836,27 +1854,26 @@ int icmp_ping(struct in_addr addr)
check_tftp_listeners(now);
#endif
if (poll_check(fd, POLLIN) &&
recvfrom(fd, &packet, sizeof(packet), 0,
(struct sockaddr *)&faddr, &len) == sizeof(packet) &&
saddr.sin_addr.s_addr == faddr.sin_addr.s_addr &&
packet.icmp.icmp_type == ICMP_ECHOREPLY &&
packet.icmp.icmp_seq == 0 &&
packet.icmp.icmp_id == id)
{
gotreply = 1;
break;
if (fd != -1)
{
struct {
struct ip ip;
struct icmp icmp;
} packet;
struct sockaddr_in faddr;
socklen_t len = sizeof(faddr);
if (poll_check(fd, POLLIN) &&
recvfrom(fd, &packet, sizeof(packet), 0, (struct sockaddr *)&faddr, &len) == sizeof(packet) &&
addr == faddr.sin_addr.s_addr &&
packet.icmp.icmp_type == ICMP_ECHOREPLY &&
packet.icmp.icmp_seq == 0 &&
packet.icmp.icmp_id == id)
return 1;
}
}
#if defined(HAVE_LINUX_NETWORK) || defined(HAVE_SOLARIS_NETWORK)
while (retry_send(close(fd)));
#else
opt = 1;
setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt));
#endif
return gotreply;
return 0;
}
#endif