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upstream: Switch the listening select loop from select() to

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pselect() and mask signals while checking signal flags, umasking for pselect
and restoring afterwards. Also restore signals before sighup_restart so they
don't remain blocked after restart.

This prevents a race where a SIGTERM or SIGHUP can arrive between
checking the flag and calling select (eg if sshd is processing a
new connection) resulting in sshd not shutting down until the next
time it receives a new connection.  bz#2158, with & ok djm@

OpenBSD-Commit-ID: bf85bf880fd78e00d7478657644fcda97b9a936f
This commit is contained in:
dtucker@openbsd.org 2021-06-04 05:09:08 +00:00 committed by Damien Miller
parent f64f8c00d1
commit 771f57a862
1 changed files with 31 additions and 14 deletions
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45
sshd.c
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@ -1,4 +1,4 @@
/* $OpenBSD: sshd.c,v 1.573 2021/05/07 03:09:38 djm Exp $ */ /* $OpenBSD: sshd.c,v 1.574 2021/06/04 05:09:08 dtucker Exp $ */
/* /*
* Author: Tatu Ylonen <ylo@cs.hut.fi> * Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -1141,6 +1141,7 @@ server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
socklen_t fromlen; socklen_t fromlen;
pid_t pid; pid_t pid;
u_char rnd[256]; u_char rnd[256];
sigset_t nsigset, osigset;
/* setup fd set for accept */ /* setup fd set for accept */
fdset = NULL; fdset = NULL;
@ -1154,11 +1155,32 @@ server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
for (i = 0; i < options.max_startups; i++) for (i = 0; i < options.max_startups; i++)
startup_pipes[i] = -1; startup_pipes[i] = -1;
/*
* Prepare signal mask that we use to block signals that might set
* received_sigterm or received_sighup, so that we are guaranteed
* to immediately wake up the pselect if a signal is received after
* the flag is checked.
*/
sigemptyset(&nsigset);
sigaddset(&nsigset, SIGHUP);
sigaddset(&nsigset, SIGCHLD);
sigaddset(&nsigset, SIGTERM);
sigaddset(&nsigset, SIGQUIT);
/* /*
* Stay listening for connections until the system crashes or * Stay listening for connections until the system crashes or
* the daemon is killed with a signal. * the daemon is killed with a signal.
*/ */
for (;;) { for (;;) {
sigprocmask(SIG_BLOCK, &nsigset, &osigset);
if (received_sigterm) {
logit("Received signal %d; terminating.",
(int) received_sigterm);
close_listen_socks();
if (options.pid_file != NULL)
unlink(options.pid_file);
exit(received_sigterm == SIGTERM ? 0 : 255);
}
if (ostartups != startups) { if (ostartups != startups) {
setproctitle("%s [listener] %d of %d-%d startups", setproctitle("%s [listener] %d of %d-%d startups",
listener_proctitle, startups, listener_proctitle, startups,
@ -1171,8 +1193,10 @@ server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
close_listen_socks(); close_listen_socks();
lameduck = 1; lameduck = 1;
} }
if (listening <= 0) if (listening <= 0) {
sigprocmask(SIG_SETMASK, &osigset, NULL);
sighup_restart(); sighup_restart();
}
} }
free(fdset); free(fdset);
fdset = xcalloc(howmany(maxfd + 1, NFDBITS), fdset = xcalloc(howmany(maxfd + 1, NFDBITS),
@ -1184,19 +1208,12 @@ server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
if (startup_pipes[i] != -1) if (startup_pipes[i] != -1)
FD_SET(startup_pipes[i], fdset); FD_SET(startup_pipes[i], fdset);
/* Wait in select until there is a connection. */ /* Wait until a connection arrives or a child exits. */
ret = select(maxfd+1, fdset, NULL, NULL, NULL); ret = pselect(maxfd+1, fdset, NULL, NULL, NULL, &osigset);
if (ret == -1 && errno != EINTR) if (ret == -1 && errno != EINTR)
error("select: %.100s", strerror(errno)); error("pselect: %.100s", strerror(errno));
if (received_sigterm) { sigprocmask(SIG_SETMASK, &osigset, NULL);
logit("Received signal %d; terminating.", if (received_sigterm)
(int) received_sigterm);
close_listen_socks();
if (options.pid_file != NULL)
unlink(options.pid_file);
exit(received_sigterm == SIGTERM ? 0 : 255);
}
if (ret == -1)
continue; continue;
for (i = 0; i < options.max_startups; i++) { for (i = 0; i < options.max_startups; i++) {