mirror of
https://github.com/pi-hole/dnsmasq.git
synced 2025-12-19 18:28:25 +00:00
Refactor poll() loop.
Handling events on file descriptors can result in new file descriptors being created or old ones being deleted. As such the results of the last call to poll() become invalid in subtle ways. After handling each file descriptor in check_dns_listeners() return, to go around the poll() loop again and get valid data for the new situation. Thanks to Dominik Derigs for his indefatigable sleuthing of this one.
This commit is contained in:
Simon Kelley
@@ -18,7 +18,7 @@
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#define MAX_PROCS 20 /* default max no children for TCP requests */
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#define MAX_PROCS 20 /* default max no children for TCP requests */
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#define CHILD_LIFETIME 150 /* secs 'till terminated (RFC1035 suggests > 120s) */
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#define CHILD_LIFETIME 150 /* secs 'till terminated (RFC1035 suggests > 120s) */
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#define TCP_MAX_QUERIES 100 /* Maximum number of queries per incoming TCP connection */
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#define TCP_MAX_QUERIES 100 /* Maximum number of queries per incoming TCP connection */
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#define TCP_TIMEOUT 1 /* timeout waiting to connect to an upstream server - double this for answer */
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#define TCP_TIMEOUT 5 /* timeout waiting to connect to an upstream server - double this for answer */
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#define TCP_BACKLOG 32 /* kernel backlog limit for TCP connections */
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#define TCP_BACKLOG 32 /* kernel backlog limit for TCP connections */
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#define EDNS_PKTSZ 1232 /* default max EDNS.0 UDP packet from from /dnsflagday.net/2020 */
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#define EDNS_PKTSZ 1232 /* default max EDNS.0 UDP packet from from /dnsflagday.net/2020 */
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#define KEYBLOCK_LEN 40 /* choose to minimise fragmentation when storing DNSSEC keys */
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#define KEYBLOCK_LEN 40 /* choose to minimise fragmentation when storing DNSSEC keys */
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476
src/dnsmasq.c
476
src/dnsmasq.c
@@ -32,6 +32,7 @@ static volatile int pipewrite;
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static void set_dns_listeners(void);
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static void set_dns_listeners(void);
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static void set_tftp_listeners(void);
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static void set_tftp_listeners(void);
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static void check_dns_listeners(time_t now);
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static void check_dns_listeners(time_t now);
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static void do_tcp_connection(struct listener *listener, time_t now);
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static void sig_handler(int sig);
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static void sig_handler(int sig);
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static void async_event(int pipe, time_t now);
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static void async_event(int pipe, time_t now);
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static void fatal_event(struct event_desc *ev, char *msg);
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static void fatal_event(struct event_desc *ev, char *msg);
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@@ -1833,246 +1834,283 @@ static void check_dns_listeners(time_t now)
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struct randfd_list *rfl;
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struct randfd_list *rfl;
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int i;
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int i;
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int pipefd[2];
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int pipefd[2];
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/* Note that handling events here can create or destroy fds and
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render the result of the last poll() call invalid. Once
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we find an fd that needs service, do it, then return to go around the
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poll() loop again. This avoid really, really, wierd bugs. */
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if (!option_bool(OPT_DEBUG))
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for (i = 0; i < daemon->max_procs; i++)
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if (daemon->tcp_pipes[i] != -1 &&
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poll_check(daemon->tcp_pipes[i], POLLIN | POLLHUP))
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{
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/* Races. The child process can die before we read all of the data from the
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pipe, or vice versa. Therefore send tcp_pids to zero when we wait() the
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process, and tcp_pipes to -1 and close the FD when we read the last
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of the data - indicated by cache_recv_insert returning zero.
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The order of these events is indeterminate, and both are needed
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to free the process slot. Once the child process has gone, poll()
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returns POLLHUP, not POLLIN, so have to check for both here. */
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if (!cache_recv_insert(now, daemon->tcp_pipes[i]))
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{
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close(daemon->tcp_pipes[i]);
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daemon->tcp_pipes[i] = -1;
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/* tcp_pipes == -1 && tcp_pids == 0 required to free slot */
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if (daemon->tcp_pids[i] == 0)
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daemon->metrics[METRIC_TCP_CONNECTIONS]--;
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}
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return;
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}
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for (serverfdp = daemon->sfds; serverfdp; serverfdp = serverfdp->next)
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for (serverfdp = daemon->sfds; serverfdp; serverfdp = serverfdp->next)
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if (poll_check(serverfdp->fd, POLLIN))
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if (poll_check(serverfdp->fd, POLLIN))
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reply_query(serverfdp->fd, now);
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{
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reply_query(serverfdp->fd, now);
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return;
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}
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for (i = 0; i < daemon->numrrand; i++)
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for (i = 0; i < daemon->numrrand; i++)
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if (daemon->randomsocks[i].refcount != 0 &&
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if (daemon->randomsocks[i].refcount != 0 &&
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poll_check(daemon->randomsocks[i].fd, POLLIN))
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poll_check(daemon->randomsocks[i].fd, POLLIN))
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reply_query(daemon->randomsocks[i].fd, now);
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{
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reply_query(daemon->randomsocks[i].fd, now);
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return;
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}
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/* Check overflow random sockets too. */
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/* Check overflow random sockets too. */
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for (rfl = daemon->rfl_poll; rfl; rfl = rfl->next)
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for (rfl = daemon->rfl_poll; rfl; rfl = rfl->next)
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if (poll_check(rfl->rfd->fd, POLLIN))
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if (poll_check(rfl->rfd->fd, POLLIN))
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reply_query(rfl->rfd->fd, now);
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{
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reply_query(rfl->rfd->fd, now);
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/* Races. The child process can die before we read all of the data from the
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return;
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pipe, or vice versa. Therefore send tcp_pids to zero when we wait() the
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}
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process, and tcp_pipes to -1 and close the FD when we read the last
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of the data - indicated by cache_recv_insert returning zero.
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The order of these events is indeterminate, and both are needed
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to free the process slot. Once the child process has gone, poll()
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returns POLLHUP, not POLLIN, so have to check for both here. */
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if (!option_bool(OPT_DEBUG))
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for (i = 0; i < daemon->max_procs; i++)
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if (daemon->tcp_pipes[i] != -1 &&
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poll_check(daemon->tcp_pipes[i], POLLIN | POLLHUP) &&
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!cache_recv_insert(now, daemon->tcp_pipes[i]))
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{
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close(daemon->tcp_pipes[i]);
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daemon->tcp_pipes[i] = -1;
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/* tcp_pipes == -1 && tcp_pids == 0 required to free slot */
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if (daemon->tcp_pids[i] == 0)
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daemon->metrics[METRIC_TCP_CONNECTIONS]--;
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}
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for (listener = daemon->listeners; listener; listener = listener->next)
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for (listener = daemon->listeners; listener; listener = listener->next)
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{
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if (listener->fd != -1 && poll_check(listener->fd, POLLIN))
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if (listener->fd != -1 && poll_check(listener->fd, POLLIN))
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{
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receive_query(listener, now);
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receive_query(listener, now);
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return;
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/* check to see if we have a free tcp process slot.
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}
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Note that we can't assume that because we had
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at least one a poll() time, that we still do.
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/* check to see if we have a free tcp process slot.
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There may be more waiting connections after
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Note that we can't assume that because we had
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poll() returns then free process slots. */
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at least one a poll() time, that we still do.
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for (i = daemon->max_procs - 1; i >= 0; i--)
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There may be more waiting connections after
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if (daemon->tcp_pids[i] == 0 && daemon->tcp_pipes[i] == -1)
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poll() returns then free process slots. */
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break;
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for (i = daemon->max_procs - 1; i >= 0; i--)
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if (daemon->tcp_pids[i] == 0 && daemon->tcp_pipes[i] == -1)
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break;
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if (listener->tcpfd != -1 && i >= 0 && poll_check(listener->tcpfd, POLLIN))
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if (i >= 0)
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for (listener = daemon->listeners; listener; listener = listener->next)
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if (listener->tcpfd != -1 && poll_check(listener->tcpfd, POLLIN))
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{
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{
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int confd, client_ok = 1;
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do_tcp_connection(listener, now);
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struct irec *iface = NULL;
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return;
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pid_t p;
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}
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union mysockaddr tcp_addr;
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}
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socklen_t tcp_len = sizeof(union mysockaddr);
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while ((confd = accept(listener->tcpfd, NULL, NULL)) == -1 && errno == EINTR);
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static void do_tcp_connection(struct listener *listener, time_t now)
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{
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if (confd == -1)
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int confd, client_ok = 1;
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continue;
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struct irec *iface = NULL;
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pid_t p;
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if (getsockname(confd, (struct sockaddr *)&tcp_addr, &tcp_len) == -1)
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union mysockaddr tcp_addr;
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{
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socklen_t tcp_len = sizeof(union mysockaddr);
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close(confd);
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unsigned char *buff;
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continue;
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struct server *s;
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}
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int flags, auth_dns, i;
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struct in_addr netmask;
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/* Make sure that the interface list is up-to-date.
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int pipefd[2];
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We do this here as we may need the results below, and
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the DNS code needs them for --interface-name stuff.
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Multiple calls to enumerate_interfaces() per select loop are
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while ((confd = accept(listener->tcpfd, NULL, NULL)) == -1 && errno == EINTR);
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inhibited, so calls to it in the child process (which doesn't select())
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have no effect. This avoids two processes reading from the same
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if (confd == -1)
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netlink fd and screwing the pooch entirely.
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return;
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*/
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if (getsockname(confd, (struct sockaddr *)&tcp_addr, &tcp_len) == -1)
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enumerate_interfaces(0);
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{
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closeconandreturn:
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shutdown(confd, SHUT_RDWR);
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close(confd);
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return;
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}
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/* Make sure that the interface list is up-to-date.
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We do this here as we may need the results below, and
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the DNS code needs them for --interface-name stuff.
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Multiple calls to enumerate_interfaces() per select loop are
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inhibited, so calls to it in the child process (which doesn't select())
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have no effect. This avoids two processes reading from the same
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netlink fd and screwing the pooch entirely.
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*/
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enumerate_interfaces(0);
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if (option_bool(OPT_NOWILD))
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iface = listener->iface; /* May be NULL */
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else
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{
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int if_index;
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char intr_name[IF_NAMESIZE];
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/* if we can find the arrival interface, check it's one that's allowed */
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if ((if_index = tcp_interface(confd, tcp_addr.sa.sa_family)) != 0 &&
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indextoname(listener->tcpfd, if_index, intr_name))
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{
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union all_addr addr;
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if (option_bool(OPT_NOWILD))
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if (tcp_addr.sa.sa_family == AF_INET6)
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iface = listener->iface; /* May be NULL */
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addr.addr6 = tcp_addr.in6.sin6_addr;
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else
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{
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int if_index;
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char intr_name[IF_NAMESIZE];
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/* if we can find the arrival interface, check it's one that's allowed */
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if ((if_index = tcp_interface(confd, tcp_addr.sa.sa_family)) != 0 &&
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indextoname(listener->tcpfd, if_index, intr_name))
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{
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union all_addr addr;
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if (tcp_addr.sa.sa_family == AF_INET6)
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addr.addr6 = tcp_addr.in6.sin6_addr;
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else
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addr.addr4 = tcp_addr.in.sin_addr;
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for (iface = daemon->interfaces; iface; iface = iface->next)
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if (iface->index == if_index &&
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iface->addr.sa.sa_family == tcp_addr.sa.sa_family)
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break;
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if (!iface && !loopback_exception(listener->tcpfd, tcp_addr.sa.sa_family, &addr, intr_name))
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client_ok = 0;
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}
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if (option_bool(OPT_CLEVERBIND))
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iface = listener->iface; /* May be NULL */
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else
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{
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/* Check for allowed interfaces when binding the wildcard address:
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we do this by looking for an interface with the same address as
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the local address of the TCP connection, then looking to see if that's
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an allowed interface. As a side effect, we get the netmask of the
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interface too, for localisation. */
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for (iface = daemon->interfaces; iface; iface = iface->next)
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if (sockaddr_isequal(&iface->addr, &tcp_addr))
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break;
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if (!iface)
|
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client_ok = 0;
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}
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}
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if (!client_ok)
|
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{
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shutdown(confd, SHUT_RDWR);
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close(confd);
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}
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else if (!option_bool(OPT_DEBUG) && pipe(pipefd) == 0 && (p = fork()) != 0)
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{
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close(pipefd[1]); /* parent needs read pipe end. */
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if (p == -1)
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close(pipefd[0]);
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else
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{
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#ifdef HAVE_LINUX_NETWORK
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/* The child process inherits the netlink socket,
|
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which it never uses, but when the parent (us)
|
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uses it in the future, the answer may go to the
|
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child, resulting in the parent blocking
|
|
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forever awaiting the result. To avoid this
|
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the child closes the netlink socket, but there's
|
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a nasty race, since the parent may use netlink
|
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before the child has done the close.
|
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|
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To avoid this, the parent blocks here until a
|
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single byte comes back up the pipe, which
|
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is sent by the child after it has closed the
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netlink socket. */
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unsigned char a;
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read_write(pipefd[0], &a, 1, RW_READ);
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#endif
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|
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/* i holds index of free slot */
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daemon->tcp_pids[i] = p;
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daemon->tcp_pipes[i] = pipefd[0];
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daemon->metrics[METRIC_TCP_CONNECTIONS]++;
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if (daemon->metrics[METRIC_TCP_CONNECTIONS] > daemon->max_procs_used)
|
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daemon->max_procs_used = daemon->metrics[METRIC_TCP_CONNECTIONS];
|
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}
|
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close(confd);
|
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|
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/* The child can use up to TCP_MAX_QUERIES ids, so skip that many. */
|
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daemon->log_id += TCP_MAX_QUERIES;
|
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#ifdef HAVE_DNSSEC
|
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/* It can do more if making DNSSEC queries too. */
|
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if (option_bool(OPT_DNSSEC_VALID))
|
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daemon->log_id += daemon->limit[LIMIT_WORK];
|
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#endif
|
|
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}
|
|
||||||
else
|
else
|
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{
|
addr.addr4 = tcp_addr.in.sin_addr;
|
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unsigned char *buff;
|
|
||||||
struct server *s;
|
for (iface = daemon->interfaces; iface; iface = iface->next)
|
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int flags;
|
if (iface->index == if_index &&
|
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struct in_addr netmask;
|
iface->addr.sa.sa_family == tcp_addr.sa.sa_family)
|
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int auth_dns;
|
break;
|
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|
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if (iface)
|
if (!iface && !loopback_exception(listener->tcpfd, tcp_addr.sa.sa_family, &addr, intr_name))
|
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{
|
client_ok = 0;
|
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netmask = iface->netmask;
|
}
|
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auth_dns = iface->dns_auth;
|
|
||||||
}
|
if (option_bool(OPT_CLEVERBIND))
|
||||||
else
|
iface = listener->iface; /* May be NULL */
|
||||||
{
|
else
|
||||||
netmask.s_addr = 0;
|
{
|
||||||
auth_dns = 0;
|
/* Check for allowed interfaces when binding the wildcard address:
|
||||||
}
|
we do this by looking for an interface with the same address as
|
||||||
|
the local address of the TCP connection, then looking to see if that's
|
||||||
/* Arrange for SIGALRM after CHILD_LIFETIME seconds to
|
an allowed interface. As a side effect, we get the netmask of the
|
||||||
terminate the process. */
|
interface too, for localisation. */
|
||||||
if (!option_bool(OPT_DEBUG))
|
|
||||||
{
|
for (iface = daemon->interfaces; iface; iface = iface->next)
|
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#ifdef HAVE_LINUX_NETWORK
|
if (sockaddr_isequal(&iface->addr, &tcp_addr))
|
||||||
/* See comment above re: netlink socket. */
|
break;
|
||||||
unsigned char a = 0;
|
|
||||||
|
if (!iface)
|
||||||
close(daemon->netlinkfd);
|
client_ok = 0;
|
||||||
read_write(pipefd[1], &a, 1, RW_WRITE);
|
|
||||||
#endif
|
|
||||||
alarm(CHILD_LIFETIME);
|
|
||||||
close(pipefd[0]); /* close read end in child. */
|
|
||||||
daemon->pipe_to_parent = pipefd[1];
|
|
||||||
}
|
|
||||||
|
|
||||||
/* The connected socket inherits non-blocking
|
|
||||||
attribute from the listening socket.
|
|
||||||
Reset that here. */
|
|
||||||
if ((flags = fcntl(confd, F_GETFL, 0)) != -1)
|
|
||||||
while(retry_send(fcntl(confd, F_SETFL, flags & ~O_NONBLOCK)));
|
|
||||||
|
|
||||||
buff = tcp_request(confd, now, &tcp_addr, netmask, auth_dns);
|
|
||||||
|
|
||||||
if (buff)
|
|
||||||
free(buff);
|
|
||||||
|
|
||||||
for (s = daemon->servers; s; s = s->next)
|
|
||||||
if (s->tcpfd != -1)
|
|
||||||
{
|
|
||||||
shutdown(s->tcpfd, SHUT_RDWR);
|
|
||||||
close(s->tcpfd);
|
|
||||||
s->tcpfd = -1;
|
|
||||||
}
|
|
||||||
|
|
||||||
if (!option_bool(OPT_DEBUG))
|
|
||||||
{
|
|
||||||
close(daemon->pipe_to_parent);
|
|
||||||
flush_log();
|
|
||||||
_exit(0);
|
|
||||||
}
|
|
||||||
}
|
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
if (!client_ok)
|
||||||
|
goto closeconandreturn;
|
||||||
|
|
||||||
|
if (!option_bool(OPT_DEBUG))
|
||||||
|
{
|
||||||
|
if (pipe(pipefd) == -1)
|
||||||
|
goto closeconandreturn; /* pipe failed */
|
||||||
|
|
||||||
|
if ((p = fork()) == -1)
|
||||||
|
{
|
||||||
|
/* fork failed */
|
||||||
|
close(pipefd[0]);
|
||||||
|
close(pipefd[1]);
|
||||||
|
goto closeconandreturn;
|
||||||
|
}
|
||||||
|
|
||||||
|
if (p != 0)
|
||||||
|
{
|
||||||
|
/* fork() done: parent side */
|
||||||
|
close(pipefd[1]); /* parent needs read pipe end. */
|
||||||
|
|
||||||
|
#ifdef HAVE_LINUX_NETWORK
|
||||||
|
/* The child process inherits the netlink socket,
|
||||||
|
which it never uses, but when the parent (us)
|
||||||
|
uses it in the future, the answer may go to the
|
||||||
|
child, resulting in the parent blocking
|
||||||
|
forever awaiting the result. To avoid this
|
||||||
|
the child closes the netlink socket, but there's
|
||||||
|
a nasty race, since the parent may use netlink
|
||||||
|
before the child has done the close.
|
||||||
|
|
||||||
|
To avoid this, the parent blocks here until a
|
||||||
|
single byte comes back up the pipe, which
|
||||||
|
is sent by the child after it has closed the
|
||||||
|
netlink socket. */
|
||||||
|
|
||||||
|
read_write(pipefd[0], buff, 1, RW_READ);
|
||||||
|
#endif
|
||||||
|
|
||||||
|
/* i holds index of free slot */
|
||||||
|
daemon->tcp_pids[i] = p;
|
||||||
|
daemon->tcp_pipes[i] = pipefd[0];
|
||||||
|
daemon->metrics[METRIC_TCP_CONNECTIONS]++;
|
||||||
|
if (daemon->metrics[METRIC_TCP_CONNECTIONS] > daemon->max_procs_used)
|
||||||
|
daemon->max_procs_used = daemon->metrics[METRIC_TCP_CONNECTIONS];
|
||||||
|
|
||||||
|
close(confd);
|
||||||
|
|
||||||
|
/* The child can use up to TCP_MAX_QUERIES ids, so skip that many. */
|
||||||
|
daemon->log_id += TCP_MAX_QUERIES;
|
||||||
|
#ifdef HAVE_DNSSEC
|
||||||
|
/* It can do more if making DNSSEC queries too. */
|
||||||
|
if (option_bool(OPT_DNSSEC_VALID))
|
||||||
|
daemon->log_id += daemon->limit[LIMIT_WORK];
|
||||||
|
#endif
|
||||||
|
|
||||||
|
return;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
if (iface)
|
||||||
|
{
|
||||||
|
netmask = iface->netmask;
|
||||||
|
auth_dns = iface->dns_auth;
|
||||||
|
}
|
||||||
|
else
|
||||||
|
{
|
||||||
|
netmask.s_addr = 0;
|
||||||
|
auth_dns = 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
/* Arrange for SIGALRM after CHILD_LIFETIME seconds to
|
||||||
|
terminate the process. */
|
||||||
|
if (!option_bool(OPT_DEBUG))
|
||||||
|
{
|
||||||
|
#ifdef HAVE_LINUX_NETWORK
|
||||||
|
/* See comment above re: netlink socket. */
|
||||||
|
unsigned char a = 0;
|
||||||
|
|
||||||
|
close(daemon->netlinkfd);
|
||||||
|
read_write(pipefd[1], &a, 1, RW_WRITE);
|
||||||
|
#endif
|
||||||
|
alarm(CHILD_LIFETIME);
|
||||||
|
close(pipefd[0]); /* close read end in child. */
|
||||||
|
daemon->pipe_to_parent = pipefd[1];
|
||||||
|
}
|
||||||
|
|
||||||
|
/* The connected socket inherits non-blocking
|
||||||
|
attribute from the listening socket.
|
||||||
|
Reset that here. */
|
||||||
|
if ((flags = fcntl(confd, F_GETFL, 0)) != -1)
|
||||||
|
while(retry_send(fcntl(confd, F_SETFL, flags & ~O_NONBLOCK)));
|
||||||
|
|
||||||
|
buff = tcp_request(confd, now, &tcp_addr, netmask, auth_dns);
|
||||||
|
|
||||||
|
if (buff)
|
||||||
|
free(buff);
|
||||||
|
|
||||||
|
for (s = daemon->servers; s; s = s->next)
|
||||||
|
if (s->tcpfd != -1)
|
||||||
|
{
|
||||||
|
shutdown(s->tcpfd, SHUT_RDWR);
|
||||||
|
close(s->tcpfd);
|
||||||
|
s->tcpfd = -1;
|
||||||
|
}
|
||||||
|
|
||||||
|
if (!option_bool(OPT_DEBUG))
|
||||||
|
{
|
||||||
|
close(daemon->pipe_to_parent);
|
||||||
|
flush_log();
|
||||||
|
_exit(0);
|
||||||
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
|
||||||
#ifdef HAVE_DNSSEC
|
#ifdef HAVE_DNSSEC
|
||||||
/* If a DNSSEC query over UDP returns a truncated answer,
|
/* If a DNSSEC query over UDP returns a truncated answer,
|
||||||
we swap to the TCP path. This routine is responsible for forking
|
we swap to the TCP path. This routine is responsible for forking
|
||||||
|
|||||||
Reference in New Issue
Block a user