kernel/bpf/reuseport_array.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (c) 2018 Facebook
   4  */
   5 #include <linux/bpf.h>
   6 #include <linux/err.h>
   7 #include <linux/sock_diag.h>
   8 #include <net/sock_reuseport.h>
   9 #include <linux/btf_ids.h>
  10
  11 struct reuseport_array {
  12         struct bpf_map map;
  13         struct sock __rcu *ptrs[];
  14 };
  15
  16 static struct reuseport_array *reuseport_array(struct bpf_map *map)
  17 {
  18         return (struct reuseport_array *)map;
  19 }
  20
  21 /* The caller must hold the reuseport_lock */
  22 void bpf_sk_reuseport_detach(struct sock *sk)
  23 {
  24         struct sock __rcu **socks;
  25
  26         write_lock_bh(&sk->sk_callback_lock);
  27         socks = __locked_read_sk_user_data_with_flags(sk, SK_USER_DATA_BPF);
  28         if (socks) {
  29                 WRITE_ONCE(sk->sk_user_data, NULL);
  30                 /*
  31                  * Do not move this NULL assignment outside of
  32                  * sk->sk_callback_lock because there is
  33                  * a race with reuseport_array_free()
  34                  * which does not hold the reuseport_lock.
  35                  */
  36                 RCU_INIT_POINTER(*socks, NULL);
  37         }
  38         write_unlock_bh(&sk->sk_callback_lock);
  39 }
  40
  41 static int reuseport_array_alloc_check(union bpf_attr *attr)
  42 {
  43         if (attr->value_size != sizeof(u32) &&
  44             attr->value_size != sizeof(u64))
  45                 return -EINVAL;
  46
  47         return array_map_alloc_check(attr);
  48 }
  49
  50 static void *reuseport_array_lookup_elem(struct bpf_map *map, void *key)
  51 {
  52         struct reuseport_array *array = reuseport_array(map);
  53         u32 index = *(u32 *)key;
  54
  55         if (unlikely(index >= array->map.max_entries))
  56                 return NULL;
  57
  58         return rcu_dereference(array->ptrs[index]);
  59 }
  60
  61 /* Called from syscall only */
  62 static long reuseport_array_delete_elem(struct bpf_map *map, void *key)
  63 {
  64         struct reuseport_array *array = reuseport_array(map);
  65         u32 index = *(u32 *)key;
  66         struct sock *sk;
  67         int err;
  68
  69         if (index >= map->max_entries)
  70                 return -E2BIG;
  71
  72         if (!rcu_access_pointer(array->ptrs[index]))
  73                 return -ENOENT;
  74
  75         spin_lock_bh(&reuseport_lock);
  76
  77         sk = rcu_dereference_protected(array->ptrs[index],
  78                                        lockdep_is_held(&reuseport_lock));
  79         if (sk) {
  80                 write_lock_bh(&sk->sk_callback_lock);
  81                 WRITE_ONCE(sk->sk_user_data, NULL);
  82                 RCU_INIT_POINTER(array->ptrs[index], NULL);
  83                 write_unlock_bh(&sk->sk_callback_lock);
  84                 err = 0;
  85         } else {
  86                 err = -ENOENT;
  87         }
  88
  89         spin_unlock_bh(&reuseport_lock);
  90
  91         return err;
  92 }
  93
  94 static void reuseport_array_free(struct bpf_map *map)
  95 {
  96         struct reuseport_array *array = reuseport_array(map);
  97         struct sock *sk;
  98         u32 i;
  99
 100         /*
 101          * ops->map_*_elem() will not be able to access this
 102          * array now. Hence, this function only races with
 103          * bpf_sk_reuseport_detach() which was triggered by
 104          * close() or disconnect().
 105          *
 106          * This function and bpf_sk_reuseport_detach() are
 107          * both removing sk from "array".  Who removes it
 108          * first does not matter.
 109          *
 110          * The only concern here is bpf_sk_reuseport_detach()
 111          * may access "array" which is being freed here.
 112          * bpf_sk_reuseport_detach() access this "array"
 113          * through sk->sk_user_data _and_ with sk->sk_callback_lock
 114          * held which is enough because this "array" is not freed
 115          * until all sk->sk_user_data has stopped referencing this "array".
 116          *
 117          * Hence, due to the above, taking "reuseport_lock" is not
 118          * needed here.
 119          */
 120
 121         /*
 122          * Since reuseport_lock is not taken, sk is accessed under
 123          * rcu_read_lock()
 124          */
 125         rcu_read_lock();
 126         for (i = 0; i < map->max_entries; i++) {
 127                 sk = rcu_dereference(array->ptrs[i]);
 128                 if (sk) {
 129                         write_lock_bh(&sk->sk_callback_lock);
 130                         /*
 131                          * No need for WRITE_ONCE(). At this point,
 132                          * no one is reading it without taking the
 133                          * sk->sk_callback_lock.
 134                          */
 135                         sk->sk_user_data = NULL;
 136                         write_unlock_bh(&sk->sk_callback_lock);
 137                         RCU_INIT_POINTER(array->ptrs[i], NULL);
 138                 }
 139         }
 140         rcu_read_unlock();
 141
 142         /*
 143          * Once reaching here, all sk->sk_user_data is not
 144          * referencing this "array". "array" can be freed now.
 145          */
 146         bpf_map_area_free(array);
 147 }
 148
 149 static struct bpf_map *reuseport_array_alloc(union bpf_attr *attr)
 150 {
 151         int numa_node = bpf_map_attr_numa_node(attr);
 152         struct reuseport_array *array;
 153
 154         /* allocate all map elements and zero-initialize them */
 155         array = bpf_map_area_alloc(struct_size(array, ptrs, attr->max_entries), numa_node);
 156         if (!array)
 157                 return ERR_PTR(-ENOMEM);
 158
 159         /* copy mandatory map attributes */
 160         bpf_map_init_from_attr(&array->map, attr);
 161
 162         return &array->map;
 163 }
 164
 165 int bpf_fd_reuseport_array_lookup_elem(struct bpf_map *map, void *key,
 166                                        void *value)
 167 {
 168         struct sock *sk;
 169         int err;
 170
 171         if (map->value_size != sizeof(u64))
 172                 return -ENOSPC;
 173
 174         rcu_read_lock();
 175         sk = reuseport_array_lookup_elem(map, key);
 176         if (sk) {
 177                 *(u64 *)value = __sock_gen_cookie(sk);
 178                 err = 0;
 179         } else {
 180                 err = -ENOENT;
 181         }
 182         rcu_read_unlock();
 183
 184         return err;
 185 }
 186
 187 static int
 188 reuseport_array_update_check(const struct reuseport_array *array,
 189                              const struct sock *nsk,
 190                              const struct sock *osk,
 191                              const struct sock_reuseport *nsk_reuse,
 192                              u32 map_flags)
 193 {
 194         if (osk && map_flags == BPF_NOEXIST)
 195                 return -EEXIST;
 196
 197         if (!osk && map_flags == BPF_EXIST)
 198                 return -ENOENT;
 199
 200         if (nsk->sk_protocol != IPPROTO_UDP && nsk->sk_protocol != IPPROTO_TCP)
 201                 return -ENOTSUPP;
 202
 203         if (nsk->sk_family != AF_INET && nsk->sk_family != AF_INET6)
 204                 return -ENOTSUPP;
 205
 206         if (nsk->sk_type != SOCK_STREAM && nsk->sk_type != SOCK_DGRAM)
 207                 return -ENOTSUPP;
 208
 209         /*
 210          * sk must be hashed (i.e. listening in the TCP case or binded
 211          * in the UDP case) and
 212          * it must also be a SO_REUSEPORT sk (i.e. reuse cannot be NULL).
 213          *
 214          * Also, sk will be used in bpf helper that is protected by
 215          * rcu_read_lock().
 216          */
 217         if (!sock_flag(nsk, SOCK_RCU_FREE) || !sk_hashed(nsk) || !nsk_reuse)
 218                 return -EINVAL;
 219
 220         /* READ_ONCE because the sk->sk_callback_lock may not be held here */
 221         if (READ_ONCE(nsk->sk_user_data))
 222                 return -EBUSY;
 223
 224         return 0;
 225 }
 226
 227 /*
 228  * Called from syscall only.
 229  * The "nsk" in the fd refcnt.
 230  * The "osk" and "reuse" are protected by reuseport_lock.
 231  */
 232 int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
 233                                        void *value, u64 map_flags)
 234 {
 235         struct reuseport_array *array = reuseport_array(map);
 236         struct sock *free_osk = NULL, *osk, *nsk;
 237         struct sock_reuseport *reuse;
 238         u32 index = *(u32 *)key;
 239         uintptr_t sk_user_data;
 240         struct socket *socket;
 241         int err, fd;
 242
 243         if (map_flags > BPF_EXIST)
 244                 return -EINVAL;
 245
 246         if (index >= map->max_entries)
 247                 return -E2BIG;
 248
 249         if (map->value_size == sizeof(u64)) {
 250                 u64 fd64 = *(u64 *)value;
 251
 252                 if (fd64 > S32_MAX)
 253                         return -EINVAL;
 254                 fd = fd64;
 255         } else {
 256                 fd = *(int *)value;
 257         }
 258
 259         socket = sockfd_lookup(fd, &err);
 260         if (!socket)
 261                 return err;
 262
 263         nsk = socket->sk;
 264         if (!nsk) {
 265                 err = -EINVAL;
 266                 goto put_file;
 267         }
 268
 269         /* Quick checks before taking reuseport_lock */
 270         err = reuseport_array_update_check(array, nsk,
 271                                            rcu_access_pointer(array->ptrs[index]),
 272                                            rcu_access_pointer(nsk->sk_reuseport_cb),
 273                                            map_flags);
 274         if (err)
 275                 goto put_file;
 276
 277         spin_lock_bh(&reuseport_lock);
 278         /*
 279          * Some of the checks only need reuseport_lock
 280          * but it is done under sk_callback_lock also
 281          * for simplicity reason.
 282          */
 283         write_lock_bh(&nsk->sk_callback_lock);
 284
 285         osk = rcu_dereference_protected(array->ptrs[index],
 286                                         lockdep_is_held(&reuseport_lock));
 287         reuse = rcu_dereference_protected(nsk->sk_reuseport_cb,
 288                                           lockdep_is_held(&reuseport_lock));
 289         err = reuseport_array_update_check(array, nsk, osk, reuse, map_flags);
 290         if (err)
 291                 goto put_file_unlock;
 292
 293         sk_user_data = (uintptr_t)&array->ptrs[index] | SK_USER_DATA_NOCOPY |
 294                 SK_USER_DATA_BPF;
 295         WRITE_ONCE(nsk->sk_user_data, (void *)sk_user_data);
 296         rcu_assign_pointer(array->ptrs[index], nsk);
 297         free_osk = osk;
 298         err = 0;
 299
 300 put_file_unlock:
 301         write_unlock_bh(&nsk->sk_callback_lock);
 302
 303         if (free_osk) {
 304                 write_lock_bh(&free_osk->sk_callback_lock);
 305                 WRITE_ONCE(free_osk->sk_user_data, NULL);
 306                 write_unlock_bh(&free_osk->sk_callback_lock);
 307         }
 308
 309         spin_unlock_bh(&reuseport_lock);
 310 put_file:
 311         sockfd_put(socket);
 312         return err;
 313 }
 314
 315 /* Called from syscall */
 316 static int reuseport_array_get_next_key(struct bpf_map *map, void *key,
 317                                         void *next_key)
 318 {
 319         struct reuseport_array *array = reuseport_array(map);
 320         u32 index = key ? *(u32 *)key : U32_MAX;
 321         u32 *next = (u32 *)next_key;
 322
 323         if (index >= array->map.max_entries) {
 324                 *next = 0;
 325                 return 0;
 326         }
 327
 328         if (index == array->map.max_entries - 1)
 329                 return -ENOENT;
 330
 331         *next = index + 1;
 332         return 0;
 333 }
 334
 335 static u64 reuseport_array_mem_usage(const struct bpf_map *map)
 336 {
 337         struct reuseport_array *array;
 338
 339         return struct_size(array, ptrs, map->max_entries);
 340 }
 341
 342 BTF_ID_LIST_SINGLE(reuseport_array_map_btf_ids, struct, reuseport_array)
 343 const struct bpf_map_ops reuseport_array_ops = {
 344         .map_meta_equal = bpf_map_meta_equal,
 345         .map_alloc_check = reuseport_array_alloc_check,
 346         .map_alloc = reuseport_array_alloc,
 347         .map_free = reuseport_array_free,
 348         .map_lookup_elem = reuseport_array_lookup_elem,
 349         .map_get_next_key = reuseport_array_get_next_key,
 350         .map_delete_elem = reuseport_array_delete_elem,
 351         .map_mem_usage = reuseport_array_mem_usage,
 352         .map_btf_id = &reuseport_array_map_btf_ids[0],
 353 };