security/landlock/task.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Landlock LSM - Ptrace hooks
   4  *
   5  * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
   6  * Copyright © 2019-2020 ANSSI
   7  */
   8
   9 #include <asm/current.h>
  10 #include <linux/cred.h>
  11 #include <linux/errno.h>
  12 #include <linux/kernel.h>
  13 #include <linux/lsm_hooks.h>
  14 #include <linux/rcupdate.h>
  15 #include <linux/sched.h>
  16 #include <net/af_unix.h>
  17 #include <net/sock.h>
  18
  19 #include "common.h"
  20 #include "cred.h"
  21 #include "fs.h"
  22 #include "ruleset.h"
  23 #include "setup.h"
  24 #include "task.h"
  25
  26 /**
  27  * domain_scope_le - Checks domain ordering for scoped ptrace
  28  *
  29  * @parent: Parent domain.
  30  * @child: Potential child of @parent.
  31  *
  32  * Checks if the @parent domain is less or equal to (i.e. an ancestor, which
  33  * means a subset of) the @child domain.
  34  */
  35 static bool domain_scope_le(const struct landlock_ruleset *const parent,
  36                             const struct landlock_ruleset *const child)
  37 {
  38         const struct landlock_hierarchy *walker;
  39
  40         if (!parent)
  41                 return true;
  42         if (!child)
  43                 return false;
  44         for (walker = child->hierarchy; walker; walker = walker->parent) {
  45                 if (walker == parent->hierarchy)
  46                         /* @parent is in the scoped hierarchy of @child. */
  47                         return true;
  48         }
  49         /* There is no relationship between @parent and @child. */
  50         return false;
  51 }
  52
  53 static bool task_is_scoped(const struct task_struct *const parent,
  54                            const struct task_struct *const child)
  55 {
  56         bool is_scoped;
  57         const struct landlock_ruleset *dom_parent, *dom_child;
  58
  59         rcu_read_lock();
  60         dom_parent = landlock_get_task_domain(parent);
  61         dom_child = landlock_get_task_domain(child);
  62         is_scoped = domain_scope_le(dom_parent, dom_child);
  63         rcu_read_unlock();
  64         return is_scoped;
  65 }
  66
  67 static int task_ptrace(const struct task_struct *const parent,
  68                        const struct task_struct *const child)
  69 {
  70         /* Quick return for non-landlocked tasks. */
  71         if (!landlocked(parent))
  72                 return 0;
  73         if (task_is_scoped(parent, child))
  74                 return 0;
  75         return -EPERM;
  76 }
  77
  78 /**
  79  * hook_ptrace_access_check - Determines whether the current process may access
  80  *                            another
  81  *
  82  * @child: Process to be accessed.
  83  * @mode: Mode of attachment.
  84  *
  85  * If the current task has Landlock rules, then the child must have at least
  86  * the same rules.  Else denied.
  87  *
  88  * Determines whether a process may access another, returning 0 if permission
  89  * granted, -errno if denied.
  90  */
  91 static int hook_ptrace_access_check(struct task_struct *const child,
  92                                     const unsigned int mode)
  93 {
  94         return task_ptrace(current, child);
  95 }
  96
  97 /**
  98  * hook_ptrace_traceme - Determines whether another process may trace the
  99  *                       current one
 100  *
 101  * @parent: Task proposed to be the tracer.
 102  *
 103  * If the parent has Landlock rules, then the current task must have the same
 104  * or more rules.  Else denied.
 105  *
 106  * Determines whether the nominated task is permitted to trace the current
 107  * process, returning 0 if permission is granted, -errno if denied.
 108  */
 109 static int hook_ptrace_traceme(struct task_struct *const parent)
 110 {
 111         return task_ptrace(parent, current);
 112 }
 113
 114 /**
 115  * domain_is_scoped - Checks if the client domain is scoped in the same
 116  *                    domain as the server.
 117  *
 118  * @client: IPC sender domain.
 119  * @server: IPC receiver domain.
 120  * @scope: The scope restriction criteria.
 121  *
 122  * Returns: True if the @client domain is scoped to access the @server,
 123  * unless the @server is also scoped in the same domain as @client.
 124  */
 125 static bool domain_is_scoped(const struct landlock_ruleset *const client,
 126                              const struct landlock_ruleset *const server,
 127                              access_mask_t scope)
 128 {
 129         int client_layer, server_layer;
 130         struct landlock_hierarchy *client_walker, *server_walker;
 131
 132         /* Quick return if client has no domain */
 133         if (WARN_ON_ONCE(!client))
 134                 return false;
 135
 136         client_layer = client->num_layers - 1;
 137         client_walker = client->hierarchy;
 138         /*
 139          * client_layer must be a signed integer with greater capacity
 140          * than client->num_layers to ensure the following loop stops.
 141          */
 142         BUILD_BUG_ON(sizeof(client_layer) > sizeof(client->num_layers));
 143
 144         server_layer = server ? (server->num_layers - 1) : -1;
 145         server_walker = server ? server->hierarchy : NULL;
 146
 147         /*
 148          * Walks client's parent domains down to the same hierarchy level
 149          * as the server's domain, and checks that none of these client's
 150          * parent domains are scoped.
 151          */
 152         for (; client_layer > server_layer; client_layer--) {
 153                 if (landlock_get_scope_mask(client, client_layer) & scope)
 154                         return true;
 155
 156                 client_walker = client_walker->parent;
 157         }
 158         /*
 159          * Walks server's parent domains down to the same hierarchy level as
 160          * the client's domain.
 161          */
 162         for (; server_layer > client_layer; server_layer--)
 163                 server_walker = server_walker->parent;
 164
 165         for (; client_layer >= 0; client_layer--) {
 166                 if (landlock_get_scope_mask(client, client_layer) & scope) {
 167                         /*
 168                          * Client and server are at the same level in the
 169                          * hierarchy. If the client is scoped, the request is
 170                          * only allowed if this domain is also a server's
 171                          * ancestor.
 172                          */
 173                         return server_walker != client_walker;
 174                 }
 175                 client_walker = client_walker->parent;
 176                 server_walker = server_walker->parent;
 177         }
 178         return false;
 179 }
 180
 181 static bool sock_is_scoped(struct sock *const other,
 182                            const struct landlock_ruleset *const domain)
 183 {
 184         const struct landlock_ruleset *dom_other;
 185
 186         /* The credentials will not change. */
 187         lockdep_assert_held(&unix_sk(other)->lock);
 188         dom_other = landlock_cred(other->sk_socket->file->f_cred)->domain;
 189         return domain_is_scoped(domain, dom_other,
 190                                 LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET);
 191 }
 192
 193 static bool is_abstract_socket(struct sock *const sock)
 194 {
 195         struct unix_address *addr = unix_sk(sock)->addr;
 196
 197         if (!addr)
 198                 return false;
 199
 200         if (addr->len >= offsetof(struct sockaddr_un, sun_path) + 1 &&
 201             addr->name->sun_path[0] == '\0')
 202                 return true;
 203
 204         return false;
 205 }
 206
 207 static const struct access_masks unix_scope = {
 208         .scope = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET,
 209 };
 210
 211 static int hook_unix_stream_connect(struct sock *const sock,
 212                                     struct sock *const other,
 213                                     struct sock *const newsk)
 214 {
 215         const struct landlock_ruleset *const dom =
 216                 landlock_get_applicable_domain(landlock_get_current_domain(),
 217                                                unix_scope);
 218
 219         /* Quick return for non-landlocked tasks. */
 220         if (!dom)
 221                 return 0;
 222
 223         if (is_abstract_socket(other) && sock_is_scoped(other, dom))
 224                 return -EPERM;
 225
 226         return 0;
 227 }
 228
 229 static int hook_unix_may_send(struct socket *const sock,
 230                               struct socket *const other)
 231 {
 232         const struct landlock_ruleset *const dom =
 233                 landlock_get_applicable_domain(landlock_get_current_domain(),
 234                                                unix_scope);
 235
 236         if (!dom)
 237                 return 0;
 238
 239         /*
 240          * Checks if this datagram socket was already allowed to be connected
 241          * to other.
 242          */
 243         if (unix_peer(sock->sk) == other->sk)
 244                 return 0;
 245
 246         if (is_abstract_socket(other->sk) && sock_is_scoped(other->sk, dom))
 247                 return -EPERM;
 248
 249         return 0;
 250 }
 251
 252 static const struct access_masks signal_scope = {
 253         .scope = LANDLOCK_SCOPE_SIGNAL,
 254 };
 255
 256 static int hook_task_kill(struct task_struct *const p,
 257                           struct kernel_siginfo *const info, const int sig,
 258                           const struct cred *const cred)
 259 {
 260         bool is_scoped;
 261         const struct landlock_ruleset *dom;
 262
 263         if (cred) {
 264                 /* Dealing with USB IO. */
 265                 dom = landlock_cred(cred)->domain;
 266         } else {
 267                 dom = landlock_get_current_domain();
 268         }
 269         dom = landlock_get_applicable_domain(dom, signal_scope);
 270
 271         /* Quick return for non-landlocked tasks. */
 272         if (!dom)
 273                 return 0;
 274
 275         rcu_read_lock();
 276         is_scoped = domain_is_scoped(dom, landlock_get_task_domain(p),
 277                                      LANDLOCK_SCOPE_SIGNAL);
 278         rcu_read_unlock();
 279         if (is_scoped)
 280                 return -EPERM;
 281
 282         return 0;
 283 }
 284
 285 static int hook_file_send_sigiotask(struct task_struct *tsk,
 286                                     struct fown_struct *fown, int signum)
 287 {
 288         const struct landlock_ruleset *dom;
 289         bool is_scoped = false;
 290
 291         /* Lock already held by send_sigio() and send_sigurg(). */
 292         lockdep_assert_held(&fown->lock);
 293         dom = landlock_get_applicable_domain(
 294                 landlock_file(fown->file)->fown_domain, signal_scope);
 295
 296         /* Quick return for unowned socket. */
 297         if (!dom)
 298                 return 0;
 299
 300         rcu_read_lock();
 301         is_scoped = domain_is_scoped(dom, landlock_get_task_domain(tsk),
 302                                      LANDLOCK_SCOPE_SIGNAL);
 303         rcu_read_unlock();
 304         if (is_scoped)
 305                 return -EPERM;
 306
 307         return 0;
 308 }
 309
 310 static struct security_hook_list landlock_hooks[] __ro_after_init = {
 311         LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
 312         LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
 313
 314         LSM_HOOK_INIT(unix_stream_connect, hook_unix_stream_connect),
 315         LSM_HOOK_INIT(unix_may_send, hook_unix_may_send),
 316
 317         LSM_HOOK_INIT(task_kill, hook_task_kill),
 318         LSM_HOOK_INIT(file_send_sigiotask, hook_file_send_sigiotask),
 319 };
 320
 321 __init void landlock_add_task_hooks(void)
 322 {
 323         security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
 324                            &landlock_lsmid);
 325 }