[openssh-commits] [openssh] 01/01: upstream: Replace SIGCHLD/notify_pipe kludge with pselect.
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dtucker pushed a commit to branch master
in repository openssh.
commit 4bdf7a04797a0ea1c431a9d54588417c29177d19
Author: dtucker at openbsd.org <dtucker at openbsd.org>
Date: Fri Jun 25 03:38:17 2021 +0000
upstream: Replace SIGCHLD/notify_pipe kludge with pselect.
Previously sshd's SIGCHLD handler would wake up select() by writing a
byte to notify_pipe. We can remove this by blocking SIGCHLD, checking
for child terminations then passing the original signal mask through
to pselect. This ensures that the pselect will immediately wake up if
a child terminates between wait()ing on them and the pselect.
In -portable, for platforms that do not have pselect the kludge is still
there but is hidden behind a pselect interface.
Based on other changes for bz#2158, ok djm@
OpenBSD-Commit-ID: 202c85de0b3bdf1744fe53529a05404c5480d813
---
serverloop.c | 108 ++++++++++++++++-------------------------------------------
1 file changed, 28 insertions(+), 80 deletions(-)
diff --git a/serverloop.c b/serverloop.c
index 70a20ab4..a2f605de 100644
--- a/serverloop.c
+++ b/serverloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: serverloop.c,v 1.226 2021/04/03 06:18:41 djm Exp $ */
+/* $OpenBSD: serverloop.c,v 1.227 2021/06/25 03:38:17 dtucker Exp $ */
/*
* Author: Tatu Ylonen <ylo at cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo at cs.hut.fi>, Espoo, Finland
@@ -88,11 +88,6 @@ extern int use_privsep;
static int no_more_sessions = 0; /* Disallow further sessions. */
-/*
- * This SIGCHLD kludge is used to detect when the child exits. The server
- * will exit after that, as soon as forwarded connections have terminated.
- */
-
static volatile sig_atomic_t child_terminated = 0; /* The child has terminated. */
/* Cleanup on signals (!use_privsep case only) */
@@ -115,59 +110,11 @@ bind_permitted(int port, uid_t uid)
return 1;
}
-/*
- * we write to this pipe if a SIGCHLD is caught in order to avoid
- * the race between select() and child_terminated
- */
-static int notify_pipe[2];
-static void
-notify_setup(void)
-{
- if (pipe(notify_pipe) == -1) {
- error("pipe(notify_pipe) failed %s", strerror(errno));
- } else if ((fcntl(notify_pipe[0], F_SETFD, FD_CLOEXEC) == -1) ||
- (fcntl(notify_pipe[1], F_SETFD, FD_CLOEXEC) == -1)) {
- error("fcntl(notify_pipe, F_SETFD) failed %s", strerror(errno));
- close(notify_pipe[0]);
- close(notify_pipe[1]);
- } else {
- set_nonblock(notify_pipe[0]);
- set_nonblock(notify_pipe[1]);
- return;
- }
- notify_pipe[0] = -1; /* read end */
- notify_pipe[1] = -1; /* write end */
-}
-static void
-notify_parent(void)
-{
- if (notify_pipe[1] != -1)
- (void)write(notify_pipe[1], "", 1);
-}
-static void
-notify_prepare(fd_set *readset)
-{
- if (notify_pipe[0] != -1)
- FD_SET(notify_pipe[0], readset);
-}
-static void
-notify_done(fd_set *readset)
-{
- char c;
-
- if (notify_pipe[0] != -1 && FD_ISSET(notify_pipe[0], readset))
- while (read(notify_pipe[0], &c, 1) != -1)
- debug2_f("reading");
-}
-
/*ARGSUSED*/
static void
sigchld_handler(int sig)
{
- int save_errno = errno;
child_terminated = 1;
- notify_parent();
- errno = save_errno;
}
/*ARGSUSED*/
@@ -211,8 +158,8 @@ client_alive_check(struct ssh *ssh)
}
/*
- * Sleep in select() until we can do something. This will initialize the
- * select masks. Upon return, the masks will indicate which descriptors
+ * Sleep in pselect() until we can do something. This will initialize the
+ * pselect masks. Upon return, the masks will indicate which descriptors
* have data or can accept data. Optionally, a maximum time can be specified
* for the duration of the wait (0 = infinite).
*/
@@ -220,16 +167,16 @@ static void
wait_until_can_do_something(struct ssh *ssh,
int connection_in, int connection_out,
fd_set **readsetp, fd_set **writesetp, int *maxfdp,
- u_int *nallocp, u_int64_t max_time_ms)
+ u_int *nallocp, u_int64_t max_time_ms, sigset_t *sigsetp)
{
- struct timeval tv, *tvp;
+ struct timespec ts, *tsp;
int ret;
time_t minwait_secs = 0;
int client_alive_scheduled = 0;
/* time we last heard from the client OR sent a keepalive */
static time_t last_client_time;
- /* Allocate and update select() masks for channel descriptors. */
+ /* Allocate and update pselect() masks for channel descriptors. */
channel_prepare_select(ssh, readsetp, writesetp, maxfdp,
nallocp, &minwait_secs);
@@ -262,7 +209,6 @@ wait_until_can_do_something(struct ssh *ssh,
if (channel_not_very_much_buffered_data())
#endif
FD_SET(connection_in, *readsetp);
- notify_prepare(*readsetp);
/*
* If we have buffered packet data going to the client, mark that
@@ -280,26 +226,26 @@ wait_until_can_do_something(struct ssh *ssh,
max_time_ms = 100;
if (max_time_ms == 0)
- tvp = NULL;
+ tsp = NULL;
else {
- tv.tv_sec = max_time_ms / 1000;
- tv.tv_usec = 1000 * (max_time_ms % 1000);
- tvp = &tv;
+ ts.tv_sec = max_time_ms / 1000;
+ ts.tv_nsec = 1000000 * (max_time_ms % 1000);
+ tsp = &ts;
}
/* Wait for something to happen, or the timeout to expire. */
- ret = select((*maxfdp)+1, *readsetp, *writesetp, NULL, tvp);
+ ret = pselect((*maxfdp)+1, *readsetp, *writesetp, NULL, tsp, sigsetp);
if (ret == -1) {
memset(*readsetp, 0, *nallocp);
memset(*writesetp, 0, *nallocp);
if (errno != EINTR)
- error("select: %.100s", strerror(errno));
+ error("pselect: %.100s", strerror(errno));
} else if (client_alive_scheduled) {
time_t now = monotime();
/*
- * If the select timed out, or returned for some other reason
+ * If the pselect timed out, or returned for some other reason
* but we haven't heard from the client in time, send keepalive.
*/
if (ret == 0 || (last_client_time != 0 && last_client_time +
@@ -310,8 +256,6 @@ wait_until_can_do_something(struct ssh *ssh,
last_client_time = now;
}
}
-
- notify_done(*readsetp);
}
/*
@@ -374,13 +318,8 @@ static void
collect_children(struct ssh *ssh)
{
pid_t pid;
- sigset_t oset, nset;
int status;
- /* block SIGCHLD while we check for dead children */
- sigemptyset(&nset);
- sigaddset(&nset, SIGCHLD);
- sigprocmask(SIG_BLOCK, &nset, &oset);
if (child_terminated) {
debug("Received SIGCHLD.");
while ((pid = waitpid(-1, &status, WNOHANG)) > 0 ||
@@ -389,7 +328,6 @@ collect_children(struct ssh *ssh)
session_close_by_pid(ssh, pid, status);
child_terminated = 0;
}
- sigprocmask(SIG_SETMASK, &oset, NULL);
}
void
@@ -399,9 +337,12 @@ server_loop2(struct ssh *ssh, Authctxt *authctxt)
int max_fd;
u_int nalloc = 0, connection_in, connection_out;
u_int64_t rekey_timeout_ms = 0;
+ sigset_t bsigset, osigset;
debug("Entering interactive session for SSH2.");
+ if (sigemptyset(&bsigset) == -1 || sigaddset(&bsigset, SIGCHLD) == -1)
+ error_f("bsigset setup: %s", strerror(errno));
ssh_signal(SIGCHLD, sigchld_handler);
child_terminated = 0;
connection_in = ssh_packet_get_connection_in(ssh);
@@ -413,10 +354,7 @@ server_loop2(struct ssh *ssh, Authctxt *authctxt)
ssh_signal(SIGQUIT, sigterm_handler);
}
- notify_setup();
-
max_fd = MAXIMUM(connection_in, connection_out);
- max_fd = MAXIMUM(max_fd, notify_pipe[0]);
server_init_dispatch(ssh);
@@ -434,8 +372,19 @@ server_loop2(struct ssh *ssh, Authctxt *authctxt)
rekey_timeout_ms = 0;
}
+ /*
+ * Block SIGCHLD while we check for dead children, then pass
+ * the old signal mask through to pselect() so that it'll wake
+ * up immediately if a child exits after we've called waitpid().
+ */
+ if (sigprocmask(SIG_BLOCK, &bsigset, &osigset) == -1)
+ error_f("bsigset sigprocmask: %s", strerror(errno));
+ collect_children(ssh);
wait_until_can_do_something(ssh, connection_in, connection_out,
- &readset, &writeset, &max_fd, &nalloc, rekey_timeout_ms);
+ &readset, &writeset, &max_fd, &nalloc, rekey_timeout_ms,
+ &osigset);
+ if (sigprocmask(SIG_UNBLOCK, &bsigset, &osigset) == -1)
+ error_f("osigset sigprocmask: %s", strerror(errno));
if (received_sigterm) {
logit("Exiting on signal %d", (int)received_sigterm);
@@ -443,7 +392,6 @@ server_loop2(struct ssh *ssh, Authctxt *authctxt)
cleanup_exit(255);
}
- collect_children(ssh);
if (!ssh_packet_is_rekeying(ssh))
channel_after_select(ssh, readset, writeset);
if (process_input(ssh, readset, connection_in) < 0)
--
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