1 /* 2 Unix SMB/Netbios implementation. 3 4 Copyright (C) Ralph Boehme 2019 5 Copyright (C) Stefan Metzmacher 2019 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 21 #include "includes.h" 22 #include "system/filesys.h" 23 #include "system/threads.h" 24 #ifdef HAVE_UNSHARE_CLONE_FS 25 #include <sched.h> 26 #endif /* HAVE_UNSHARE_CLONE_FS */ 27 28 static bool _per_thread_cwd_checked; 29 static bool _per_thread_cwd_supported; 30 #ifdef HAVE_UNSHARE_CLONE_FS 31 static __thread bool _per_thread_cwd_disabled; 32 static __thread bool _per_thread_cwd_activated; 33 #endif /* HAVE_UNSHARE_CLONE_FS */ 34 35 /* 36 * This is the first function to be called! 37 * Typically in the main() function before 38 * any threads are created. 39 * 40 * This can be called multiple times 41 * as the result is cached the first time. 42 */ per_thread_cwd_check(void)43void per_thread_cwd_check(void) 44 { 45 if (_per_thread_cwd_checked) { 46 return; 47 } 48 49 #ifdef HAVE_UNSHARE_CLONE_FS 50 /* 51 * While unshare(CLONE_FS) is available on 52 * Linux for ages, unshare() is also 53 * used to implement containers with various 54 * per container namespaces. 55 * 56 * It's possible that the whole unshare() 57 * is blocked in order to disallow neested 58 * containers. 59 * 60 * That's why we sadly need a runtime check 61 * for this. 62 */ 63 { 64 int res; 65 66 res = unshare(CLONE_FS); 67 if (res == 0) { 68 _per_thread_cwd_supported = true; 69 } 70 } 71 72 /* 73 * We're in the main thread, so we should disallow 74 * per_thread_cwd_activate() here. 75 */ 76 _per_thread_cwd_disabled = true; 77 #endif /* HAVE_UNSHARE_CLONE_FS */ 78 79 _per_thread_cwd_checked = true; 80 } 81 82 /* 83 * In order to use per_thread_cwd_supported() 84 * per_thread_cwd_check() needs to be called first! 85 * Otherwise an assert will be triggered! 86 */ per_thread_cwd_supported(void)87bool per_thread_cwd_supported(void) 88 { 89 SMB_ASSERT(_per_thread_cwd_checked); 90 return _per_thread_cwd_supported; 91 } 92 93 /* 94 * In order to use per_thread_cwd_disable() 95 * should be called after any fork() in order 96 * to mark the main thread of the process, 97 * which should disallow per_thread_cwd_activate(). 98 * 99 * This can be called without calling 100 * per_thread_cwd_check() first. 101 * 102 * And it can't be called after calling 103 * per_thread_cwd_activate()! 104 * Otherwise an assert will be triggered! 105 * 106 * This can be called multiple times 107 * as the result is cached the first time. 108 */ per_thread_cwd_disable(void)109void per_thread_cwd_disable(void) 110 { 111 #ifdef HAVE_UNSHARE_CLONE_FS 112 SMB_ASSERT(!_per_thread_cwd_activated); 113 if (_per_thread_cwd_disabled) { 114 return; 115 } 116 _per_thread_cwd_disabled = true; 117 #endif /* HAVE_UNSHARE_CLONE_FS */ 118 } 119 120 /* 121 * In order to use per_thread_cwd_activate() 122 * per_thread_cwd_supported() needs to be checked first! 123 * Otherwise an assert will be triggered! 124 * 125 * This MUST only be called within helper threads! 126 * 127 * That means it can't be called after calling 128 * per_thread_cwd_disable()! 129 * Otherwise an assert will be triggered! 130 * 131 * This can be called multiple times 132 * as the result is cached the first time. 133 */ per_thread_cwd_activate(void)134void per_thread_cwd_activate(void) 135 { 136 SMB_ASSERT(_per_thread_cwd_checked); 137 SMB_ASSERT(_per_thread_cwd_supported); 138 139 #ifdef HAVE_UNSHARE_CLONE_FS 140 if (_per_thread_cwd_activated) { 141 return; 142 } 143 144 SMB_ASSERT(!_per_thread_cwd_disabled); 145 146 { 147 int ret; 148 ret = unshare(CLONE_FS); 149 SMB_ASSERT(ret == 0); 150 } 151 152 _per_thread_cwd_activated = true; 153 #else /* not HAVE_UNSHARE_CLONE_FS */ 154 smb_panic(__location__); 155 #endif /* not HAVE_UNSHARE_CLONE_FS */ 156 } 157