1/* euidaccess-stat -- check if effective user id can access lstat'd file 2 This function is probably useful only for choosing whether to issue 3 a prompt in an implementation of POSIX-specified rm. 4 5 Copyright (C) 2005-2006, 2009-2010 Free Software Foundation, Inc. 6 7 This program is free software: you can redistribute it and/or modify 8 it under the terms of the GNU General Public License as published by 9 the Free Software Foundation, either version 3 of the License, or 10 (at your option) any later version. 11 12 This program is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 19 20/* Adapted for use in GNU remove.c by Jim Meyering. */ 21 22#include <config.h> 23 24#include "euidaccess-stat.h" 25 26#include <unistd.h> 27 28#include "group-member.h" 29#include "stat-macros.h" 30 31/* Return true if the current user has permission of type MODE 32 on the file from which stat buffer *ST was obtained, ignoring 33 ACLs, attributes, `read-only'ness, etc... 34 Otherwise, return false. 35 36 Like the reentrant version of euidaccess, but starting with 37 a stat buffer rather than a file name. Hence, this function 38 never calls access or accessx, and doesn't take into account 39 whether the file has ACLs or other attributes, or resides on 40 a read-only file system. */ 41 42bool 43euidaccess_stat (struct stat const *st, int mode) 44{ 45 uid_t euid; 46 unsigned int granted; 47 48 /* Convert the mode to traditional form, clearing any bogus bits. */ 49 if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0) 50 mode &= 7; 51 else 52 mode = ((mode & R_OK ? 4 : 0) 53 + (mode & W_OK ? 2 : 0) 54 + (mode & X_OK ? 1 : 0)); 55 56 if (mode == 0) 57 return true; /* The file exists. */ 58 59 euid = geteuid (); 60 61 /* The super-user can read and write any file, and execute any file 62 that anyone can execute. */ 63 if (euid == 0 && ((mode & X_OK) == 0 64 || (st->st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)))) 65 return true; 66 67 /* Convert the file's permission bits to traditional form. */ 68 if ( S_IRUSR == (4 << 6) 69 && S_IWUSR == (2 << 6) 70 && S_IXUSR == (1 << 6) 71 && S_IRGRP == (4 << 3) 72 && S_IWGRP == (2 << 3) 73 && S_IXGRP == (1 << 3) 74 && S_IROTH == (4 << 0) 75 && S_IWOTH == (2 << 0) 76 && S_IXOTH == (1 << 0)) 77 granted = st->st_mode; 78 else 79 granted = ( (st->st_mode & S_IRUSR ? 4 << 6 : 0) 80 + (st->st_mode & S_IWUSR ? 2 << 6 : 0) 81 + (st->st_mode & S_IXUSR ? 1 << 6 : 0) 82 + (st->st_mode & S_IRGRP ? 4 << 3 : 0) 83 + (st->st_mode & S_IWGRP ? 2 << 3 : 0) 84 + (st->st_mode & S_IXGRP ? 1 << 3 : 0) 85 + (st->st_mode & S_IROTH ? 4 << 0 : 0) 86 + (st->st_mode & S_IWOTH ? 2 << 0 : 0) 87 + (st->st_mode & S_IXOTH ? 1 << 0 : 0)); 88 89 if (euid == st->st_uid) 90 granted >>= 6; 91 else 92 { 93 gid_t egid = getegid (); 94 if (egid == st->st_gid || group_member (st->st_gid)) 95 granted >>= 3; 96 } 97 98 if ((mode & ~granted) == 0) 99 return true; 100 101 return false; 102} 103 104 105#ifdef TEST 106# include <errno.h> 107# include <stdio.h> 108# include <stdlib.h> 109 110# include "error.h" 111# define _(msg) msg 112 113char *program_name; 114 115int 116main (int argc, char **argv) 117{ 118 char *file; 119 int mode; 120 bool ok; 121 struct stat st; 122 123 program_name = argv[0]; 124 if (argc < 3) 125 abort (); 126 file = argv[1]; 127 mode = atoi (argv[2]); 128 if (lstat (file, &st) != 0) 129 error (EXIT_FAILURE, errno, _("cannot stat %s"), file); 130 131 ok = euidaccess_stat (&st, mode); 132 printf ("%s: %s\n", file, ok ? "y" : "n"); 133 return 0; 134} 135#endif 136