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/* Retrieve the umask of the process (multithread-safe).
Copyright (C) 2020 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Bruno Haible <bruno@clisp.org>, 2020. */
/* There are three ways to implement a getumask() function on systems that
don't have it:
(a) Through system calls on the file system.
(b) Through a global variable that the main() function has to set,
together with an override of the umask() function.
(c) Through { mode_t mask = umask (0); umask (mask); }.
Each has its drawbacks:
(a) Causes additional system calls. May fail in some rare cases.
(b) Causes globally visible code complexity / maintainer effort.
(c) Is not multithread-safe: open() calls in other threads may
create files with wrong access permissions.
Here we implement (a), as the least evil. */
#include <config.h>
/* The package may define ASSUME_UMASK_CONSTANT to 1, to indicate that the
program does not call umask(). */
/* #define ASSUME_UMASK_CONSTANT 1 */
/* Specification. */
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "clean-temp.h"
#include "tempname.h"
mode_t
getumask (void)
{
#if 0
/* This is not multithread-safe! */
mode_t mask = umask (0);
umask (mask);
return mask;
#else
# if ASSUME_UMASK_CONSTANT
static int cached_umask = -1;
if (cached_umask >= 0)
return cached_umask;
# endif
int mask = -1;
# if defined __linux__
{
/* In Linux >= 4.7, the umask can be retrieved from an "Umask:" line in the
/proc/self/status file. */
char buf[4096];
int fd = open ("/proc/self/status", O_RDONLY);
if (fd >= 0)
{
ssize_t n = read (fd, buf, sizeof (buf));
if (n > 0)
{
const char *p_end = buf + n;
const char *p = buf;
for (;;)
{
/* Here we're at the beginning of a line. */
if (p_end - p > 8 && memcmp (p, "Umask:\t0", 8) == 0)
{
unsigned int value = 0;
p += 8;
for (; p < p_end && *p >= '0' && *p <= '7'; p++)
value = 8 * value + (*p - '0');
if (p < p_end && *p == '\n')
mask = value;
break;
}
/* Search the start of the next line. */
for (; p < p_end && *p != '\n'; p++)
;
if (p == p_end)
break;
p++;
}
}
close (fd);
}
}
# endif
if (mask < 0)
{
/* Create a temporary file and inspect its access permissions. */
const char *tmpdir = getenv ("TMPDIR");
if (tmpdir == NULL || *tmpdir == '\0')
tmpdir = "/tmp";
size_t tmpdir_length = strlen (tmpdir);
char *temp_filename = (char *) malloc (tmpdir_length + 15 + 1);
if (temp_filename != NULL)
{
memcpy (temp_filename, tmpdir, tmpdir_length);
strcpy (temp_filename + tmpdir_length, "/gtumask.XXXXXX");
int fd = gen_register_open_temp (temp_filename, 0, O_RDWR,
S_IRWXU|S_IRWXG|S_IRWXO);
if (fd >= 0)
{
struct stat statbuf;
if (fstat (fd, &statbuf) >= 0)
mask = (S_IRWXU|S_IRWXG|S_IRWXO) & ~statbuf.st_mode;
close_temp (fd);
cleanup_temporary_file (temp_filename, false);
}
free (temp_filename);
}
}
if (mask < 0)
{
/* We still don't know! Assume a paranoid user. */
mask = 077;
}
# if ASSUME_UMASK_CONSTANT
cached_umask = mask;
# endif
return mask;
#endif
}
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