Use vfork instead of posix_spawn

WARNING: This is an experimental fix for the race conditions
         reported at ksh93#79 and att#468. There may
         be bugs that have not yet been caught.

This patch replaces usage of posix_spawn with vfork, since the
former is prone to race conditions.

src/lib/libast/features/lib,
src/lib/libast/comp/spawnveg.c:
- Remove the posix_spawn implementation of spawnveg.
- Set the terminal process group between fork/vfork and execve
  to fix a race condition.

src/cmd/ksh93/sh/xec.c:
- Set the terminal process group on error to fix a vfork(2) lockup
  and crash with fork(2); both occured after the to the spawnveg fix.

src/cmd/ksh93/sh/xec.c

@@ -3724,12 +3724,16 @@ static pid_t sh_ntfork(Shell_t *shp,const Shnode_t *t,char *argv[],int *jobid,in
 	fail:
 		if(jobfork && spawnpid<0) 
 			job_fork(0);
-		if(spawnpid < 0) switch(errno=shp->path_err)
+		if(spawnpid < 0)
 		{
-		    case ENOENT:
-			errormsg(SH_DICT,ERROR_system(ERROR_NOENT),e_found+4);
-		    default:
-			errormsg(SH_DICT,ERROR_system(ERROR_NOEXEC),e_exec+4);
+			tcsetpgrp(2,job.curpgid);
+			switch(errno=shp->path_err)
+			{
+			    case ENOENT:
+				errormsg(SH_DICT,ERROR_system(ERROR_NOENT),e_found+4);
+			    default:
+				errormsg(SH_DICT,ERROR_system(ERROR_NOEXEC),e_exec+4);
+			}
 		}
 	}
 	else

src/lib/libast/comp/spawnveg.c

@@ -38,51 +38,6 @@ NoN(spawnveg)
 
 #else
 
-#if _lib_posix_spawn > 1	/* reports underlying exec() errors */
-
-#include <spawn.h>
-#include <error.h>
-#include <wait.h>
-
-pid_t
-spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
-{
-	int			err;
-	pid_t			pid;
-	posix_spawnattr_t	attr;
-
-	if (err = posix_spawnattr_init(&attr))
-		goto nope;
-	if (pgid)
-	{
-		if (pgid <= 1)
-			pgid = 0;
-		if (err = posix_spawnattr_setpgroup(&attr, pgid))
-			goto bad;
-		if (err = posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETPGROUP))
-			goto bad;
-	}
-	if (err = posix_spawn(&pid, path, NiL, &attr, argv, envv ? envv : environ))
-		goto bad;
-	posix_spawnattr_destroy(&attr);
-#if _lib_posix_spawn < 2
-	if (waitpid(pid, &err, WNOHANG|WNOWAIT) == pid && EXIT_STATUS(err) == 127)
-	{
-		while (waitpid(pid, NiL, 0) == -1 && errno == EINTR);
-		if (!access(path, X_OK))
-			errno = ENOEXEC;
-		pid = -1;
-	}
-#endif
-	return pid;
- bad:
-	posix_spawnattr_destroy(&attr);
- nope:
-	errno = err;
-	return -1;
-}
-
-#else
 
 #if _lib_spawn_mode
 
@@ -211,7 +166,11 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 		{
 			m = 0;
 			if (pgid == 1 || pgid == -2 && (m = 1))
+			{
 				pgid = getpid();
+				if (!m)
+					tcsetpgrp(2, pgid);
+			}
 			if (setpgid(0, pgid) < 0 && errno == EPERM)
 				setpgid(pgid, 0);
 #if _lib_tcgetpgrp
@@ -291,6 +250,5 @@ spawnveg(const char* path, char* const argv[], char* const envv[], pid_t pgid)
 
 #endif
 
-#endif
 
 #endif

src/lib/libast/features/lib

@@ -241,120 +241,6 @@ tst	real_vfork note{ vfork child shares data with parent }end execute{
 	}
 }end
 
-tst	lib_posix_spawn unistd.h stdlib.h spawn.h -Dfork=______fork note{ posix_spawn exists and it works and its worth using }end status{
-	#include <sys/types.h>
-	#include <sys/stat.h>
-	#include <sys/wait.h>
-	#include <spawn.h>
-	#include <signal.h>
-	#include <fcntl.h>
-	#include <string.h>
-	/* if it uses fork() why bother? */
-	#undef fork
-	pid_t fork _ARG_((void)) { NOTE("uses fork()"); return -1; }
-	pid_t _fork _ARG_((void)) { NOTE("uses _fork()"); return -1; }
-	pid_t __fork _ARG_((void)) { NOTE("uses __fork()"); return -1; }
-	int
-	main(argc, argv)
-	int	argc;
-	char**	argv;
-	{
-		char*			s;
-		pid_t			pid;
-		posix_spawnattr_t	attr;
-		int			n;
-		int			status;
-		char*			cmd[3];
-		char			tmp[1024];
-		if (argv[1])
-			_exit(signal(SIGHUP, SIG_DFL) != SIG_IGN);
-		signal(SIGHUP, SIG_IGN);
-		if (posix_spawnattr_init(&attr))
-		{
-			NOTE("posix_spawnattr_init() FAILED");
-			_exit(0);
-		}
-		if (posix_spawnattr_setpgroup(&attr, 0))
-		{
-			NOTE("posix_spawnattr_setpgroup() FAILED");
-			_exit(0);
-		}
-		if (posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETPGROUP))
-		{
-			NOTE("posix_spawnattr_setflags() FAILED");
-			_exit(0);
-		}
-		/* first try an a.out and verify that SIGHUP is ignored */
-		cmd[0] = argv[0];
-		cmd[1] = "test";
-		cmd[2] = 0;
-		if (posix_spawn(&pid, cmd[0], 0, &attr, cmd, 0))
-		{
-			NOTE("posix_spawn() FAILED");
-			_exit(0);
-		}
-		status = 1;
-		if (wait(&status) < 0)
-		{
-			NOTE("wait() FAILED");
-			_exit(0);
-		}
-		if (status != 0)
-		{
-			NOTE("SIGHUP ignored in parent not ignored in child");
-			_exit(0);
-		}
-		/* must return exec-type errors or its useless to us *unless* there is no [v]fork() */
-		n = strlen(cmd[0]);
-		if (n >= (sizeof(tmp) - 3))
-		{
-			NOTE("test executable path too long");
-			_exit(0);
-		}
-		strcpy(tmp, cmd[0]);
-		tmp[n] = '.';
-		tmp[n+1] = 's';
-		tmp[n+2] = 'h';
-		tmp[n+3] = 0;
-		if ((n = open(tmp, O_CREAT|O_WRONLY, S_IRWXU|S_IRWXG|S_IRWXO)) < 0 ||
-		    chmod(tmp, S_IRWXU|S_IRWXG|S_IRWXO) < 0 ||
-		    write(n, "exit 99\n", 8) != 8 ||
-		    close(n) < 0)
-		{
-			NOTE("test script create FAILED");
-			_exit(0);
-		}
-		cmd[0] = tmp;
-		n = 0; /* 0 means reject */
-		pid = -1;
-		if (posix_spawn(&pid, cmd[0], 0, &attr, cmd, 0))
-		{
-			n = 2;
-			NOTE("ENOEXEC produces posix_spawn() error (BEST)");
-		}
-		else if (pid == -1)
-			NOTE("ENOEXEC returns pid == -1");
-		else if (wait(&status) != pid)
-			NOTE("ENOEXEC produces no child process");
-		else if (!WIFEXITED(status))
-			NOTE("ENOEXEC produces signal exit");
-		else
-		{
-			status = WEXITSTATUS(status);
-			if (status == 127)
-			{
-				n = 1;
-				NOTE("ENOEXEC produces exit status 127 (GOOD)");
-			}
-			else if (status == 99)
-				NOTE("ENOEXEC invokes sh");
-			else if (status == 0)
-				NOTE("ENOEXEC reports no error");
-		}
-		_exit(n);
- 	}
-}end
-
 tst	lib_spawn_mode unistd.h stdlib.h note{ first spawn arg is mode and it works }end execute{
 	#include <signal.h>
 	#include <process.h>
@@ -689,7 +575,7 @@ tst	- output{
 		printf("\n");
 	#endif
 
-	#if _lib_spawnveg || _lib_posix_spawn || _lib_spawn_mode || _lib_spawn && _hdr_spawn && _mem_pgroup_inheritance || _lib_vfork && _real_vfork
+	#if _lib_spawnveg || _lib_spawn_mode || _lib_spawn && _hdr_spawn && _mem_pgroup_inheritance || _lib_vfork && _real_vfork
 		printf("#if !_AST_no_spawnveg\n");
 		printf("#define _use_spawnveg	1\n");
 		printf("#endif\n");