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/* libguestfs
* Copyright (C) 2016 Red Hat Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* Return current umask in a thread-safe way.
*
* glibc documents, but does not actually implement, a "getumask(3)"
* call.
*
* We use C<Umask> from F</proc/self/status> for Linux E<ge> 4.7.
* For older Linux and other Unix, this file implements an expensive
* but thread-safe way to get the current process's umask.
*
* Thanks to: Josh Stone, Jiri Jaburek, Eric Blake.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include "ignore-value.h"
#include "guestfs.h"
#include "guestfs-internal.h"
static int get_umask_from_proc (guestfs_h *g);
static int get_umask_from_fork (guestfs_h *g);
/**
* Returns the current process's umask. On failure, returns C<-1> and
* sets the error in the guestfs handle.
*/
int
guestfs_int_getumask (guestfs_h *g)
{
int mask;
mask = get_umask_from_proc (g);
if (mask == -1)
return -1;
if (mask >= 0)
return mask;
return get_umask_from_fork (g);
}
/**
* For Linux E<ge> 4.7 get the umask from F</proc/self/status>.
*
* On failure this returns C<-1>. However if we could not open the
* F</proc> file or find the C<Umask> entry in it, return C<-2> which
* causes the fallback path to run.
*/
static int
get_umask_from_proc (guestfs_h *g)
{
CLEANUP_FCLOSE FILE *fp = NULL;
CLEANUP_FREE char *line = NULL;
size_t allocsize = 0;
ssize_t len;
unsigned int mask;
bool found = false;
fp = fopen ("/proc/self/status", "r");
if (fp == NULL) {
if (errno == ENOENT || errno == ENOTDIR)
return -2; /* fallback */
perrorf (g, "open: /proc/self/status");
return -1;
}
while ((len = getline (&line, &allocsize, fp)) != -1) {
if (len > 0 && line[len-1] == '\n')
line[--len] = '\0';
/* Looking for: "Umask: 0022" */
if (sscanf (line, "Umask: %o", &mask) == 1) {
found = true;
break;
}
}
if (!found)
return -2; /* fallback */
return (int) mask;
}
/**
* Fallback method of getting the umask using fork.
*/
static int
get_umask_from_fork (guestfs_h *g)
{
pid_t pid;
int fd[2], r;
int mask;
int status;
r = pipe2 (fd, O_CLOEXEC);
if (r == -1) {
perrorf (g, "pipe2");
return -1;
}
pid = fork ();
if (pid == -1) {
perrorf (g, "fork");
close (fd[0]);
close (fd[1]);
return -1;
}
if (pid == 0) {
/* The child process must ONLY call async-safe functions. */
close (fd[0]);
/* umask can't fail. */
mask = umask (0);
if (write (fd[1], &mask, sizeof mask) != sizeof mask)
_exit (EXIT_FAILURE);
if (close (fd[1]) == -1)
_exit (EXIT_FAILURE);
_exit (EXIT_SUCCESS);
}
/* Parent. */
close (fd[1]);
/* Read the umask. */
if (read (fd[0], &mask, sizeof mask) != sizeof mask) {
perrorf (g, "read");
close (fd[0]);
guestfs_int_waitpid_noerror (pid);
return -1;
}
close (fd[0]);
if (guestfs_int_waitpid (g, pid, &status, "umask") == -1)
return -1;
else if (!WIFEXITED (status) || WEXITSTATUS (status) != 0) {
guestfs_int_external_command_failed (g, status, "umask", NULL);
return -1;
}
return mask;
}
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