Kees Cook | 2d51448 | 2011-12-21 12:17:04 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Yama Linux Security Module |
| 3 | * |
| 4 | * Author: Kees Cook <keescook@chromium.org> |
| 5 | * |
| 6 | * Copyright (C) 2010 Canonical, Ltd. |
| 7 | * Copyright (C) 2011 The Chromium OS Authors. |
| 8 | * |
| 9 | * This program is free software; you can redistribute it and/or modify |
| 10 | * it under the terms of the GNU General Public License version 2, as |
| 11 | * published by the Free Software Foundation. |
| 12 | * |
| 13 | */ |
| 14 | |
| 15 | #include <linux/security.h> |
| 16 | #include <linux/sysctl.h> |
| 17 | #include <linux/ptrace.h> |
| 18 | #include <linux/prctl.h> |
| 19 | #include <linux/ratelimit.h> |
| 20 | |
| 21 | static int ptrace_scope = 1; |
| 22 | |
| 23 | /* describe a ptrace relationship for potential exception */ |
| 24 | struct ptrace_relation { |
| 25 | struct task_struct *tracer; |
| 26 | struct task_struct *tracee; |
| 27 | struct list_head node; |
| 28 | }; |
| 29 | |
| 30 | static LIST_HEAD(ptracer_relations); |
| 31 | static DEFINE_SPINLOCK(ptracer_relations_lock); |
| 32 | |
| 33 | /** |
| 34 | * yama_ptracer_add - add/replace an exception for this tracer/tracee pair |
| 35 | * @tracer: the task_struct of the process doing the ptrace |
| 36 | * @tracee: the task_struct of the process to be ptraced |
| 37 | * |
| 38 | * Each tracee can have, at most, one tracer registered. Each time this |
| 39 | * is called, the prior registered tracer will be replaced for the tracee. |
| 40 | * |
| 41 | * Returns 0 if relationship was added, -ve on error. |
| 42 | */ |
| 43 | static int yama_ptracer_add(struct task_struct *tracer, |
| 44 | struct task_struct *tracee) |
| 45 | { |
| 46 | int rc = 0; |
| 47 | struct ptrace_relation *added; |
| 48 | struct ptrace_relation *entry, *relation = NULL; |
| 49 | |
| 50 | added = kmalloc(sizeof(*added), GFP_KERNEL); |
| 51 | if (!added) |
| 52 | return -ENOMEM; |
| 53 | |
| 54 | spin_lock_bh(&ptracer_relations_lock); |
| 55 | list_for_each_entry(entry, &ptracer_relations, node) |
| 56 | if (entry->tracee == tracee) { |
| 57 | relation = entry; |
| 58 | break; |
| 59 | } |
| 60 | if (!relation) { |
| 61 | relation = added; |
| 62 | relation->tracee = tracee; |
| 63 | list_add(&relation->node, &ptracer_relations); |
| 64 | } |
| 65 | relation->tracer = tracer; |
| 66 | |
| 67 | spin_unlock_bh(&ptracer_relations_lock); |
| 68 | if (added != relation) |
| 69 | kfree(added); |
| 70 | |
| 71 | return rc; |
| 72 | } |
| 73 | |
| 74 | /** |
| 75 | * yama_ptracer_del - remove exceptions related to the given tasks |
| 76 | * @tracer: remove any relation where tracer task matches |
| 77 | * @tracee: remove any relation where tracee task matches |
| 78 | */ |
| 79 | static void yama_ptracer_del(struct task_struct *tracer, |
| 80 | struct task_struct *tracee) |
| 81 | { |
| 82 | struct ptrace_relation *relation, *safe; |
| 83 | |
| 84 | spin_lock_bh(&ptracer_relations_lock); |
| 85 | list_for_each_entry_safe(relation, safe, &ptracer_relations, node) |
| 86 | if (relation->tracee == tracee || |
Kees Cook | bf06189 | 2012-02-14 16:48:09 -0800 | [diff] [blame] | 87 | (tracer && relation->tracer == tracer)) { |
Kees Cook | 2d51448 | 2011-12-21 12:17:04 -0800 | [diff] [blame] | 88 | list_del(&relation->node); |
| 89 | kfree(relation); |
| 90 | } |
| 91 | spin_unlock_bh(&ptracer_relations_lock); |
| 92 | } |
| 93 | |
| 94 | /** |
| 95 | * yama_task_free - check for task_pid to remove from exception list |
| 96 | * @task: task being removed |
| 97 | */ |
| 98 | static void yama_task_free(struct task_struct *task) |
| 99 | { |
| 100 | yama_ptracer_del(task, task); |
| 101 | } |
| 102 | |
| 103 | /** |
| 104 | * yama_task_prctl - check for Yama-specific prctl operations |
| 105 | * @option: operation |
| 106 | * @arg2: argument |
| 107 | * @arg3: argument |
| 108 | * @arg4: argument |
| 109 | * @arg5: argument |
| 110 | * |
| 111 | * Return 0 on success, -ve on error. -ENOSYS is returned when Yama |
| 112 | * does not handle the given option. |
| 113 | */ |
| 114 | static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3, |
| 115 | unsigned long arg4, unsigned long arg5) |
| 116 | { |
| 117 | int rc; |
| 118 | struct task_struct *myself = current; |
| 119 | |
| 120 | rc = cap_task_prctl(option, arg2, arg3, arg4, arg5); |
| 121 | if (rc != -ENOSYS) |
| 122 | return rc; |
| 123 | |
| 124 | switch (option) { |
| 125 | case PR_SET_PTRACER: |
| 126 | /* Since a thread can call prctl(), find the group leader |
| 127 | * before calling _add() or _del() on it, since we want |
| 128 | * process-level granularity of control. The tracer group |
| 129 | * leader checking is handled later when walking the ancestry |
| 130 | * at the time of PTRACE_ATTACH check. |
| 131 | */ |
| 132 | rcu_read_lock(); |
| 133 | if (!thread_group_leader(myself)) |
| 134 | myself = rcu_dereference(myself->group_leader); |
| 135 | get_task_struct(myself); |
| 136 | rcu_read_unlock(); |
| 137 | |
| 138 | if (arg2 == 0) { |
| 139 | yama_ptracer_del(NULL, myself); |
| 140 | rc = 0; |
Kees Cook | 36afb82 | 2012-08-27 11:38:13 -0700 | [diff] [blame] | 141 | } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) { |
Kees Cook | bf06189 | 2012-02-14 16:48:09 -0800 | [diff] [blame] | 142 | rc = yama_ptracer_add(NULL, myself); |
Kees Cook | 2d51448 | 2011-12-21 12:17:04 -0800 | [diff] [blame] | 143 | } else { |
| 144 | struct task_struct *tracer; |
| 145 | |
| 146 | rcu_read_lock(); |
| 147 | tracer = find_task_by_vpid(arg2); |
| 148 | if (tracer) |
| 149 | get_task_struct(tracer); |
| 150 | else |
| 151 | rc = -EINVAL; |
| 152 | rcu_read_unlock(); |
| 153 | |
| 154 | if (tracer) { |
| 155 | rc = yama_ptracer_add(tracer, myself); |
| 156 | put_task_struct(tracer); |
| 157 | } |
| 158 | } |
| 159 | |
| 160 | put_task_struct(myself); |
| 161 | break; |
| 162 | } |
| 163 | |
| 164 | return rc; |
| 165 | } |
| 166 | |
| 167 | /** |
| 168 | * task_is_descendant - walk up a process family tree looking for a match |
| 169 | * @parent: the process to compare against while walking up from child |
| 170 | * @child: the process to start from while looking upwards for parent |
| 171 | * |
| 172 | * Returns 1 if child is a descendant of parent, 0 if not. |
| 173 | */ |
| 174 | static int task_is_descendant(struct task_struct *parent, |
| 175 | struct task_struct *child) |
| 176 | { |
| 177 | int rc = 0; |
| 178 | struct task_struct *walker = child; |
| 179 | |
| 180 | if (!parent || !child) |
| 181 | return 0; |
| 182 | |
| 183 | rcu_read_lock(); |
| 184 | if (!thread_group_leader(parent)) |
| 185 | parent = rcu_dereference(parent->group_leader); |
| 186 | while (walker->pid > 0) { |
| 187 | if (!thread_group_leader(walker)) |
| 188 | walker = rcu_dereference(walker->group_leader); |
| 189 | if (walker == parent) { |
| 190 | rc = 1; |
| 191 | break; |
| 192 | } |
| 193 | walker = rcu_dereference(walker->real_parent); |
| 194 | } |
| 195 | rcu_read_unlock(); |
| 196 | |
| 197 | return rc; |
| 198 | } |
| 199 | |
| 200 | /** |
| 201 | * ptracer_exception_found - tracer registered as exception for this tracee |
| 202 | * @tracer: the task_struct of the process attempting ptrace |
| 203 | * @tracee: the task_struct of the process to be ptraced |
| 204 | * |
| 205 | * Returns 1 if tracer has is ptracer exception ancestor for tracee. |
| 206 | */ |
| 207 | static int ptracer_exception_found(struct task_struct *tracer, |
| 208 | struct task_struct *tracee) |
| 209 | { |
| 210 | int rc = 0; |
| 211 | struct ptrace_relation *relation; |
| 212 | struct task_struct *parent = NULL; |
Kees Cook | bf06189 | 2012-02-14 16:48:09 -0800 | [diff] [blame] | 213 | bool found = false; |
Kees Cook | 2d51448 | 2011-12-21 12:17:04 -0800 | [diff] [blame] | 214 | |
| 215 | spin_lock_bh(&ptracer_relations_lock); |
| 216 | rcu_read_lock(); |
| 217 | if (!thread_group_leader(tracee)) |
| 218 | tracee = rcu_dereference(tracee->group_leader); |
| 219 | list_for_each_entry(relation, &ptracer_relations, node) |
| 220 | if (relation->tracee == tracee) { |
| 221 | parent = relation->tracer; |
Kees Cook | bf06189 | 2012-02-14 16:48:09 -0800 | [diff] [blame] | 222 | found = true; |
Kees Cook | 2d51448 | 2011-12-21 12:17:04 -0800 | [diff] [blame] | 223 | break; |
| 224 | } |
| 225 | |
Kees Cook | bf06189 | 2012-02-14 16:48:09 -0800 | [diff] [blame] | 226 | if (found && (parent == NULL || task_is_descendant(parent, tracer))) |
Kees Cook | 2d51448 | 2011-12-21 12:17:04 -0800 | [diff] [blame] | 227 | rc = 1; |
| 228 | rcu_read_unlock(); |
| 229 | spin_unlock_bh(&ptracer_relations_lock); |
| 230 | |
| 231 | return rc; |
| 232 | } |
| 233 | |
| 234 | /** |
| 235 | * yama_ptrace_access_check - validate PTRACE_ATTACH calls |
| 236 | * @child: task that current task is attempting to ptrace |
| 237 | * @mode: ptrace attach mode |
| 238 | * |
| 239 | * Returns 0 if following the ptrace is allowed, -ve on error. |
| 240 | */ |
| 241 | static int yama_ptrace_access_check(struct task_struct *child, |
| 242 | unsigned int mode) |
| 243 | { |
| 244 | int rc; |
| 245 | |
| 246 | /* If standard caps disallows it, so does Yama. We should |
| 247 | * only tighten restrictions further. |
| 248 | */ |
| 249 | rc = cap_ptrace_access_check(child, mode); |
| 250 | if (rc) |
| 251 | return rc; |
| 252 | |
| 253 | /* require ptrace target be a child of ptracer on attach */ |
| 254 | if (mode == PTRACE_MODE_ATTACH && |
| 255 | ptrace_scope && |
| 256 | !task_is_descendant(current, child) && |
| 257 | !ptracer_exception_found(current, child) && |
| 258 | !capable(CAP_SYS_PTRACE)) |
| 259 | rc = -EPERM; |
| 260 | |
| 261 | if (rc) { |
| 262 | char name[sizeof(current->comm)]; |
| 263 | printk_ratelimited(KERN_NOTICE "ptrace of non-child" |
| 264 | " pid %d was attempted by: %s (pid %d)\n", |
| 265 | child->pid, |
| 266 | get_task_comm(name, current), |
| 267 | current->pid); |
| 268 | } |
| 269 | |
| 270 | return rc; |
| 271 | } |
| 272 | |
| 273 | static struct security_operations yama_ops = { |
| 274 | .name = "yama", |
| 275 | |
| 276 | .ptrace_access_check = yama_ptrace_access_check, |
| 277 | .task_prctl = yama_task_prctl, |
| 278 | .task_free = yama_task_free, |
| 279 | }; |
| 280 | |
| 281 | #ifdef CONFIG_SYSCTL |
| 282 | static int zero; |
| 283 | static int one = 1; |
| 284 | |
| 285 | struct ctl_path yama_sysctl_path[] = { |
| 286 | { .procname = "kernel", }, |
| 287 | { .procname = "yama", }, |
| 288 | { } |
| 289 | }; |
| 290 | |
| 291 | static struct ctl_table yama_sysctl_table[] = { |
| 292 | { |
| 293 | .procname = "ptrace_scope", |
| 294 | .data = &ptrace_scope, |
| 295 | .maxlen = sizeof(int), |
| 296 | .mode = 0644, |
| 297 | .proc_handler = proc_dointvec_minmax, |
| 298 | .extra1 = &zero, |
| 299 | .extra2 = &one, |
| 300 | }, |
| 301 | { } |
| 302 | }; |
| 303 | #endif /* CONFIG_SYSCTL */ |
| 304 | |
| 305 | static __init int yama_init(void) |
| 306 | { |
| 307 | if (!security_module_enable(&yama_ops)) |
| 308 | return 0; |
| 309 | |
| 310 | printk(KERN_INFO "Yama: becoming mindful.\n"); |
| 311 | |
| 312 | if (register_security(&yama_ops)) |
| 313 | panic("Yama: kernel registration failed.\n"); |
| 314 | |
| 315 | #ifdef CONFIG_SYSCTL |
| 316 | if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table)) |
| 317 | panic("Yama: sysctl registration failed.\n"); |
| 318 | #endif |
| 319 | |
| 320 | return 0; |
| 321 | } |
| 322 | |
| 323 | security_initcall(yama_init); |