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/* euidaccess-stat -- check if effective user id can access lstat'd file
This function is probably useful only for choosing whether to issue
a prompt in an implementation of POSIX-specified rm.
Copyright (C) 2005, 2006, 2009 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 <http://www.gnu.org/licenses/>. */
/* Adapted for use in GNU remove.c by Jim Meyering. */
#include <config.h>
#include "euidaccess-stat.h"
#include <unistd.h>
#include "group-member.h"
#include "stat-macros.h"
/* Return true if the current user has permission of type MODE
on the file from which stat buffer *ST was obtained, ignoring
ACLs, attributes, `read-only'ness, etc...
Otherwise, return false.
Like the reentrant version of euidaccess, but starting with
a stat buffer rather than a file name. Hence, this function
never calls access or accessx, and doesn't take into account
whether the file has ACLs or other attributes, or resides on
a read-only file system. */
bool
euidaccess_stat (struct stat const *st, int mode)
{
uid_t euid;
unsigned int granted;
/* Convert the mode to traditional form, clearing any bogus bits. */
if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
mode &= 7;
else
mode = ((mode & R_OK ? 4 : 0)
+ (mode & W_OK ? 2 : 0)
+ (mode & X_OK ? 1 : 0));
if (mode == 0)
return true; /* The file exists. */
euid = geteuid ();
/* The super-user can read and write any file, and execute any file
that anyone can execute. */
if (euid == 0 && ((mode & X_OK) == 0
|| (st->st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
return true;
/* Convert the file's permission bits to traditional form. */
if ( S_IRUSR == (4 << 6)
&& S_IWUSR == (2 << 6)
&& S_IXUSR == (1 << 6)
&& S_IRGRP == (4 << 3)
&& S_IWGRP == (2 << 3)
&& S_IXGRP == (1 << 3)
&& S_IROTH == (4 << 0)
&& S_IWOTH == (2 << 0)
&& S_IXOTH == (1 << 0))
granted = st->st_mode;
else
granted = ( (st->st_mode & S_IRUSR ? 4 << 6 : 0)
+ (st->st_mode & S_IWUSR ? 2 << 6 : 0)
+ (st->st_mode & S_IXUSR ? 1 << 6 : 0)
+ (st->st_mode & S_IRGRP ? 4 << 3 : 0)
+ (st->st_mode & S_IWGRP ? 2 << 3 : 0)
+ (st->st_mode & S_IXGRP ? 1 << 3 : 0)
+ (st->st_mode & S_IROTH ? 4 << 0 : 0)
+ (st->st_mode & S_IWOTH ? 2 << 0 : 0)
+ (st->st_mode & S_IXOTH ? 1 << 0 : 0));
if (euid == st->st_uid)
granted >>= 6;
else
{
gid_t egid = getegid ();
if (egid == st->st_gid || group_member (st->st_gid))
granted >>= 3;
}
if ((mode & ~granted) == 0)
return true;
return false;
}
#ifdef TEST
# include <errno.h>
# include <stdio.h>
# include <stdlib.h>
# include "error.h"
# define _(msg) msg
char *program_name;
int
main (int argc, char **argv)
{
char *file;
int mode;
bool ok;
struct stat st;
program_name = argv[0];
if (argc < 3)
abort ();
file = argv[1];
mode = atoi (argv[2]);
if (lstat (file, &st) != 0)
error (EXIT_FAILURE, errno, _("cannot stat %s"), file);
ok = euidaccess_stat (&st, mode);
printf ("%s: %s\n", file, ok ? "y" : "n");
exit (0);
}
#endif
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