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Prevent abnormal termination of a child daemon process when created

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by a parent that is a session leader (e.g., login shell) by ignoring
SIGHUP in before calling fork(2) and then restoring SIGHUP's action
after setsid(3).  Based on the patch by Martin Kammerhofer
<mkamm@gmx.net>.

PR:		bin/25462
Reviewed by:	bde, alex.neyman@auriga.ru
This commit is contained in:
Guy Helmer 2003-11-10 22:01:42 +00:00
parent 2c85cbd9b5
commit 8b2b22e84d
2 changed files with 35 additions and 3 deletions
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17
lib/libc/gen/daemon.3
View File

@ -71,12 +71,13 @@ The
function may fail and set
.Va errno
for any of the errors specified for the library functions
.Xr fork 2
.Xr fork 2 ,
and
.Xr setsid 2 .
.Sh SEE ALSO
.Xr fork 2 ,
.Xr setsid 2
.Xr setsid 2 ,
.Xr sigaction 2
.Sh HISTORY
The
.Fn daemon
@ -101,3 +102,15 @@ should therefore either call
.Fn daemon
before opening any files or sockets, or verify that any file
descriptors obtained have values greater than 2.
.Pp
The
.Fn daemon
function temporarily ignores
.Dv SIGHUP
while calling
.Xr setsid 2
to prevent a parent session group leader's calls to
.Xr fork 2
and then
.Xr _exit 2
from prematurely terminating the child process.

21
lib/libc/gen/daemon.c
View File

@ -38,8 +38,10 @@ static char sccsid[] = "@(#)daemon.c 8.1 (Berkeley) 6/4/93";
__FBSDID("$FreeBSD$");
#include "namespace.h"
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <signal.h>
#include <unistd.h>
#include "un-namespace.h"
@ -47,7 +49,17 @@ int
daemon(nochdir, noclose)
int nochdir, noclose;
{
struct sigaction osa, sa;
int fd;
pid_t newgrp;
int oerrno;
int osa_ok;
/* A SIGHUP may be thrown when the parent exits below. */
sigemptyset(&sa.sa_mask);
sa.sa_handler = SIG_IGN;
sa.sa_flags = 0;
osa_ok = _sigaction(SIGHUP, &sa, &osa);
switch (fork()) {
case -1:
@ -58,8 +70,15 @@ daemon(nochdir, noclose)
_exit(0);
}
if (setsid() == -1)
newgrp = setsid();
oerrno = errno;
if (osa_ok != -1)
_sigaction(SIGHUP, &osa, NULL);
if (newgrp == -1) {
errno = oerrno;
return (-1);
}
if (!nochdir)
(void)chdir("/");