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Simplify pselect shim and remove side effects.

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Instead of maintaing state (pipe descriptors, signal handlers) across
pselect-on-select invocations, set up and restore them each call.
This prevents outside factors (eg a closefrom or signal handler
installation) from potentially causing problems.  This does result in a
drop in throughput of a couple of percent on geriatric platforms without
a native pselect due to the extra overhead.  Tweaks & ok djm@
This commit is contained in:
Darren Tucker 2024-10-25 19:01:02 +11:00
parent e53b615f39
commit 326495744f
No known key found for this signature in database
1 changed files with 52 additions and 56 deletions
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108
openbsd-compat/bsd-pselect.c
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@ -40,75 +40,47 @@
#include <unistd.h>
#include "log.h"
#include "misc.h" /* for set_nonblock */
#ifndef HAVE_SIGHANDLER_T
typedef void (*sighandler_t)(int);
#endif
static sighandler_t saved_sighandler[_NSIG];
static int notify_pipe[2]; /* 0 = read end, 1 = write end */
/*
* Set up the descriptors. Because they are close-on-exec, in the case
* where sshd's re-exec fails notify_pipe will still point to a descriptor
* that was closed by the exec attempt but if that descriptor has been
* reopened then we'll attempt to use that. Ensure that notify_pipe is
* outside of the range used by sshd re-exec but within NFDBITS (so we don't
* need to expand the fd_sets).
* Because the debugging for this is so noisy, we only output on the first
* call, and suppress it thereafter.
*/
#define REEXEC_MIN_FREE_FD (STDERR_FILENO + 4)
static int
pselect_notify_setup_fd(int *fd)
{
int r;
static int suppress_debug;
if ((r = fcntl(*fd, F_DUPFD, REEXEC_MIN_FREE_FD)) < 0 ||
fcntl(r, F_SETFD, FD_CLOEXEC) < 0 || r >= FD_SETSIZE)
return -1;
(void)close(*fd);
return (*fd = r);
static void
pselect_set_nonblock(int fd)
{
int val;
if ((val = fcntl(fd, F_GETFL)) == -1 ||
fcntl(fd, F_SETFL, val|O_NONBLOCK) == -1)
error_f("fcntl: %s", strerror(errno));
}
/*
* we write to this pipe if a SIGCHLD is caught in order to avoid
* the race between select() and child_terminated
* the race between select() and child_terminated.
*/
static pid_t notify_pid;
static int notify_pipe[2];
static void
static int
pselect_notify_setup(void)
{
static int initialized;
if (initialized && notify_pid == getpid())
return;
if (notify_pid == 0)
debug3_f("initializing");
else {
debug3_f("pid changed, reinitializing");
if (notify_pipe[0] != -1)
close(notify_pipe[0]);
if (notify_pipe[1] != -1)
close(notify_pipe[1]);
}
if (pipe(notify_pipe) == -1) {
error("pipe(notify_pipe) failed %s", strerror(errno));
} else if (pselect_notify_setup_fd(&notify_pipe[0]) == -1 ||
pselect_notify_setup_fd(&notify_pipe[1]) == -1) {
error("fcntl(notify_pipe, ...) failed %s", strerror(errno));
close(notify_pipe[0]);
close(notify_pipe[1]);
} else {
set_nonblock(notify_pipe[0]);
set_nonblock(notify_pipe[1]);
notify_pid = getpid();
debug3_f("pid %d saved %d pipe0 %d pipe1 %d", getpid(),
notify_pid, notify_pipe[0], notify_pipe[1]);
initialized = 1;
return;
notify_pipe[0] = notify_pipe[1] = -1;
return -1;
}
notify_pipe[0] = -1; /* read end */
notify_pipe[1] = -1; /* write end */
pselect_set_nonblock(notify_pipe[0]);
pselect_set_nonblock(notify_pipe[1]);
if (!suppress_debug)
debug3_f("pipe0 %d pipe1 %d", notify_pipe[0], notify_pipe[1]);
return 0;
}
static void
pselect_notify_parent(void)
@ -132,6 +104,8 @@ pselect_notify_done(fd_set *readset)
debug2_f("reading");
FD_CLR(notify_pipe[0], readset);
}
(void)close(notify_pipe[0]);
(void)close(notify_pipe[1]);
}
/*ARGSUSED*/
@ -167,26 +141,29 @@ pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
if (mask == NULL) /* no signal mask, just call select */
return select(nfds, readfds, writefds, exceptfds, tvp);
/* For each signal we're unmasking, install our handler if needed. */
/* For each signal unmasked, save old handler and install ours. */
for (sig = 0; sig < _NSIG; sig++) {
saved_sighandler[sig] = NULL;
if (sig == SIGKILL || sig == SIGSTOP || sigismember(mask, sig))
continue;
if (sigaction(sig, NULL, &sa) == 0 &&
sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL) {
unmasked = 1;
if (sa.sa_handler == pselect_sig_handler)
continue;
sa.sa_handler = pselect_sig_handler;
if (sigaction(sig, &sa, &osa) == 0) {
debug3_f("installing signal handler for %s, "
"previous %p", strsignal(sig),
osa.sa_handler);
if (!suppress_debug)
debug3_f("installed signal handler for"
" %s, previous 0x%p",
strsignal(sig), osa.sa_handler);
saved_sighandler[sig] = osa.sa_handler;
}
}
}
if (unmasked) {
pselect_notify_setup();
if ((ret = pselect_notify_setup()) == -1) {
saved_errno = ENOMEM;
goto out;
}
pselect_notify_prepare(readfds);
nfds = MAX(nfds, notify_pipe[0] + 1);
}
@ -199,6 +176,25 @@ pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
if (unmasked)
pselect_notify_done(readfds);
out:
/* Restore signal handlers. */
for (sig = 0; sig < _NSIG; sig++) {
if (saved_sighandler[sig] == NULL)
continue;
if (sigaction(sig, NULL, &sa) == 0) {
sa.sa_handler = saved_sighandler[sig];
if (sigaction(sig, &sa, NULL) == 0) {
if (!suppress_debug)
debug3_f("restored signal handler for "
"%s", strsignal(sig));
} else {
error_f("failed to restore signal handler for "
"%s: %s", strsignal(sig), strerror(errno));
}
}
}
suppress_debug = 1;
errno = saved_errno;
return ret;
}