[src/trunk]: src/lib/libc/stdlib system(3): Switch from vfork/execve to posix...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/404781ec07ee
branches:  trunk
changeset: 363905:404781ec07ee
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Mar 14 22:06:28 2022 +0000

description:
system(3): Switch from vfork/execve to posix_spawn.

Changes by me:
- Minor style nits.
- Set errno on posix_spawn failure.
- Handle edge cases of SIGINT/SIGQUIT set to SIG_IGN by caller.


Author: Nikita Ronja Gillmann <nikita%NetBSD.org@localhost>
Committer: Taylor R Campbell <riastradh%NetBSD.org@localhost>

diffstat:

 lib/libc/stdlib/system.c |  59 +++++++++++++++++++++++++++++++++--------------
 1 files changed, 41 insertions(+), 18 deletions(-)

diffs (105 lines):

diff -r ce8eb915fe4c -r 404781ec07ee lib/libc/stdlib/system.c
--- a/lib/libc/stdlib/system.c  Mon Mar 14 21:38:04 2022 +0000
+++ b/lib/libc/stdlib/system.c  Mon Mar 14 22:06:28 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: system.c,v 1.26 2021/10/29 19:27:06 kre Exp $  */
+/*     $NetBSD: system.c,v 1.27 2022/03/14 22:06:28 riastradh Exp $    */
 
 /*
  * Copyright (c) 1988, 1993
@@ -34,7 +34,7 @@
 #if 0
 static char sccsid[] = "@(#)system.c   8.1 (Berkeley) 6/4/93";
 #else
-__RCSID("$NetBSD: system.c,v 1.26 2021/10/29 19:27:06 kre Exp $");
+__RCSID("$NetBSD: system.c,v 1.27 2022/03/14 22:06:28 riastradh Exp $");
 #endif
 #endif /* LIBC_SCCS and not lint */
 
@@ -46,6 +46,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <paths.h>
+#include <spawn.h>
 
 #include "env.h"
 
@@ -54,9 +55,12 @@
 {
        pid_t pid;
        struct sigaction intsa, quitsa, sa;
-       sigset_t nmask, omask;
+       sigset_t nmask, omask, sigdefault;
        int pstat;
        const char *argp[] = {"sh", "-c", "--", NULL, NULL};
+       posix_spawnattr_t attr;
+       int error;
+
        argp[3] = command;
 
        /*
@@ -88,22 +92,41 @@
                return -1;
        }
 
+       /*
+        * We arrange to inherit all signal handlers from the caller by
+        * default, except possibly SIGINT and SIGQUIT.  These we have
+        * overridden internally for system(3) to be SIG_IGN.
+        *
+        * - If the caller had SIGINT or SIGQUIT at SIG_IGN, then we
+        *   inherit them as is -- caller had SIG_IGN, child will too.
+        *
+        * - Otherwise, they are SIG_DFL or a signal handler, and we
+        *   must reset them to SIG_DFL in the child, rather than
+        *   SIG_IGN in system(3) in the parent, by including them in
+        *   the sigdefault set.
+        */
+       sigemptyset(&sigdefault);
+       if (intsa.sa_handler != SIG_IGN)
+               sigaddset(&sigdefault, SIGINT);
+       if (quitsa.sa_handler != SIG_IGN)
+               sigaddset(&sigdefault, SIGQUIT);
+
+       posix_spawnattr_init(&attr);
+       posix_spawnattr_setsigdefault(&attr, &sigdefault);
+       posix_spawnattr_setsigmask(&attr, &omask);
+       posix_spawnattr_setflags(&attr,
+           POSIX_SPAWN_SETSIGDEF|POSIX_SPAWN_SETSIGMASK);
        (void)__readlockenv();
-       switch(pid = vfork()) {
-       case -1:                        /* error */
-               (void)__unlockenv();
-               sigaction(SIGINT, &intsa, NULL);
-               sigaction(SIGQUIT, &quitsa, NULL);
-               (void)sigprocmask(SIG_SETMASK, &omask, NULL);
-               return -1;
-       case 0:                         /* child */
-               sigaction(SIGINT, &intsa, NULL);
-               sigaction(SIGQUIT, &quitsa, NULL);
-               (void)sigprocmask(SIG_SETMASK, &omask, NULL);
-               execve(_PATH_BSHELL, __UNCONST(argp), environ);
-               _exit(127);
+       error = posix_spawn(&pid, _PATH_BSHELL, NULL, &attr, __UNCONST(argp),
+           environ);
+       (void)__unlockenv();
+       posix_spawnattr_destroy(&attr);
+
+       if (error) {
+               errno = error;
+               pstat = -1;
+               goto out;
        }
-       (void)__unlockenv();
 
        while (waitpid(pid, &pstat, 0) == -1) {
                if (errno != EINTR) {
@@ -112,7 +135,7 @@
                }
        }
 
-       sigaction(SIGINT, &intsa, NULL);
+out:   sigaction(SIGINT, &intsa, NULL);
        sigaction(SIGQUIT, &quitsa, NULL);
        (void)sigprocmask(SIG_SETMASK, &omask, NULL);