root/kernel/bpf/reuseport_array.c

DEFINITIONS

1. bpf_sk_reuseport_detach
2. reuseport_array_alloc_check
3. reuseport_array_lookup_elem
4. reuseport_array_delete_elem
5. reuseport_array_free
6. reuseport_array_alloc
7. bpf_fd_reuseport_array_lookup_elem
8. reuseport_array_update_check
9. bpf_fd_reuseport_array_update_elem
10. reuseport_array_get_next_key

   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 
  10 struct reuseport_array {
  11         struct bpf_map map;
  12         struct sock __rcu *ptrs[];
  13 };
  14 
  15 static struct reuseport_array *reuseport_array(struct bpf_map *map)
  16 {
  17         return (struct reuseport_array *)map;
  18 }
  19 
  20 /* The caller must hold the reuseport_lock */
  21 void bpf_sk_reuseport_detach(struct sock *sk)
  22 {
  23         struct sock __rcu **socks;
  24 
  25         write_lock_bh(&sk->sk_callback_lock);
  26         socks = sk->sk_user_data;
  27         if (socks) {
  28                 WRITE_ONCE(sk->sk_user_data, NULL);
  29                 /*
  30                  * Do not move this NULL assignment outside of
  31                  * sk->sk_callback_lock because there is
  32                  * a race with reuseport_array_free()
  33                  * which does not hold the reuseport_lock.
  34                  */
  35                 RCU_INIT_POINTER(*socks, NULL);
  36         }
  37         write_unlock_bh(&sk->sk_callback_lock);
  38 }
  39 
  40 static int reuseport_array_alloc_check(union bpf_attr *attr)
  41 {
  42         if (attr->value_size != sizeof(u32) &&
  43             attr->value_size != sizeof(u64))
  44                 return -EINVAL;
  45 
  46         return array_map_alloc_check(attr);
  47 }
  48 
  49 static void *reuseport_array_lookup_elem(struct bpf_map *map, void *key)
  50 {
  51         struct reuseport_array *array = reuseport_array(map);
  52         u32 index = *(u32 *)key;
  53 
  54         if (unlikely(index >= array->map.max_entries))
  55                 return NULL;
  56 
  57         return rcu_dereference(array->ptrs[index]);
  58 }
  59 
  60 /* Called from syscall only */
  61 static int reuseport_array_delete_elem(struct bpf_map *map, void *key)
  62 {
  63         struct reuseport_array *array = reuseport_array(map);
  64         u32 index = *(u32 *)key;
  65         struct sock *sk;
  66         int err;
  67 
  68         if (index >= map->max_entries)
  69                 return -E2BIG;
  70 
  71         if (!rcu_access_pointer(array->ptrs[index]))
  72                 return -ENOENT;
  73 
  74         spin_lock_bh(&reuseport_lock);
  75 
  76         sk = rcu_dereference_protected(array->ptrs[index],
  77                                        lockdep_is_held(&reuseport_lock));
  78         if (sk) {
  79                 write_lock_bh(&sk->sk_callback_lock);
  80                 WRITE_ONCE(sk->sk_user_data, NULL);
  81                 RCU_INIT_POINTER(array->ptrs[index], NULL);
  82                 write_unlock_bh(&sk->sk_callback_lock);
  83                 err = 0;
  84         } else {
  85                 err = -ENOENT;
  86         }
  87 
  88         spin_unlock_bh(&reuseport_lock);
  89 
  90         return err;
  91 }
  92 
  93 static void reuseport_array_free(struct bpf_map *map)
  94 {
  95         struct reuseport_array *array = reuseport_array(map);
  96         struct sock *sk;
  97         u32 i;
  98 
  99         synchronize_rcu();
 100 
 101         /*
 102          * ops->map_*_elem() will not be able to access this
 103          * array now. Hence, this function only races with
 104          * bpf_sk_reuseport_detach() which was triggerred by
 105          * close() or disconnect().
 106          *
 107          * This function and bpf_sk_reuseport_detach() are
 108          * both removing sk from "array".  Who removes it
 109          * first does not matter.
 110          *
 111          * The only concern here is bpf_sk_reuseport_detach()
 112          * may access "array" which is being freed here.
 113          * bpf_sk_reuseport_detach() access this "array"
 114          * through sk->sk_user_data _and_ with sk->sk_callback_lock
 115          * held which is enough because this "array" is not freed
 116          * until all sk->sk_user_data has stopped referencing this "array".
 117          *
 118          * Hence, due to the above, taking "reuseport_lock" is not
 119          * needed here.
 120          */
 121 
 122         /*
 123          * Since reuseport_lock is not taken, sk is accessed under
 124          * rcu_read_lock()
 125          */
 126         rcu_read_lock();
 127         for (i = 0; i < map->max_entries; i++) {
 128                 sk = rcu_dereference(array->ptrs[i]);
 129                 if (sk) {
 130                         write_lock_bh(&sk->sk_callback_lock);
 131                         /*
 132                          * No need for WRITE_ONCE(). At this point,
 133                          * no one is reading it without taking the
 134                          * sk->sk_callback_lock.
 135                          */
 136                         sk->sk_user_data = NULL;
 137                         write_unlock_bh(&sk->sk_callback_lock);
 138                         RCU_INIT_POINTER(array->ptrs[i], NULL);
 139                 }
 140         }
 141         rcu_read_unlock();
 142 
 143         /*
 144          * Once reaching here, all sk->sk_user_data is not
 145          * referenceing this "array".  "array" can be freed now.
 146          */
 147         bpf_map_area_free(array);
 148 }
 149 
 150 static struct bpf_map *reuseport_array_alloc(union bpf_attr *attr)
 151 {
 152         int err, numa_node = bpf_map_attr_numa_node(attr);
 153         struct reuseport_array *array;
 154         struct bpf_map_memory mem;
 155         u64 array_size;
 156 
 157         if (!capable(CAP_SYS_ADMIN))
 158                 return ERR_PTR(-EPERM);
 159 
 160         array_size = sizeof(*array);
 161         array_size += (u64)attr->max_entries * sizeof(struct sock *);
 162 
 163         err = bpf_map_charge_init(&mem, array_size);
 164         if (err)
 165                 return ERR_PTR(err);
 166 
 167         /* allocate all map elements and zero-initialize them */
 168         array = bpf_map_area_alloc(array_size, numa_node);
 169         if (!array) {
 170                 bpf_map_charge_finish(&mem);
 171                 return ERR_PTR(-ENOMEM);
 172         }
 173 
 174         /* copy mandatory map attributes */
 175         bpf_map_init_from_attr(&array->map, attr);
 176         bpf_map_charge_move(&array->map.memory, &mem);
 177 
 178         return &array->map;
 179 }
 180 
 181 int bpf_fd_reuseport_array_lookup_elem(struct bpf_map *map, void *key,
 182                                        void *value)
 183 {
 184         struct sock *sk;
 185         int err;
 186 
 187         if (map->value_size != sizeof(u64))
 188                 return -ENOSPC;
 189 
 190         rcu_read_lock();
 191         sk = reuseport_array_lookup_elem(map, key);
 192         if (sk) {
 193                 *(u64 *)value = sock_gen_cookie(sk);
 194                 err = 0;
 195         } else {
 196                 err = -ENOENT;
 197         }
 198         rcu_read_unlock();
 199 
 200         return err;
 201 }
 202 
 203 static int
 204 reuseport_array_update_check(const struct reuseport_array *array,
 205                              const struct sock *nsk,
 206                              const struct sock *osk,
 207                              const struct sock_reuseport *nsk_reuse,
 208                              u32 map_flags)
 209 {
 210         if (osk && map_flags == BPF_NOEXIST)
 211                 return -EEXIST;
 212 
 213         if (!osk && map_flags == BPF_EXIST)
 214                 return -ENOENT;
 215 
 216         if (nsk->sk_protocol != IPPROTO_UDP && nsk->sk_protocol != IPPROTO_TCP)
 217                 return -ENOTSUPP;
 218 
 219         if (nsk->sk_family != AF_INET && nsk->sk_family != AF_INET6)
 220                 return -ENOTSUPP;
 221 
 222         if (nsk->sk_type != SOCK_STREAM && nsk->sk_type != SOCK_DGRAM)
 223                 return -ENOTSUPP;
 224 
 225         /*
 226          * sk must be hashed (i.e. listening in the TCP case or binded
 227          * in the UDP case) and
 228          * it must also be a SO_REUSEPORT sk (i.e. reuse cannot be NULL).
 229          *
 230          * Also, sk will be used in bpf helper that is protected by
 231          * rcu_read_lock().
 232          */
 233         if (!sock_flag(nsk, SOCK_RCU_FREE) || !sk_hashed(nsk) || !nsk_reuse)
 234                 return -EINVAL;
 235 
 236         /* READ_ONCE because the sk->sk_callback_lock may not be held here */
 237         if (READ_ONCE(nsk->sk_user_data))
 238                 return -EBUSY;
 239 
 240         return 0;
 241 }
 242 
 243 /*
 244  * Called from syscall only.
 245  * The "nsk" in the fd refcnt.
 246  * The "osk" and "reuse" are protected by reuseport_lock.
 247  */
 248 int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
 249                                        void *value, u64 map_flags)
 250 {
 251         struct reuseport_array *array = reuseport_array(map);
 252         struct sock *free_osk = NULL, *osk, *nsk;
 253         struct sock_reuseport *reuse;
 254         u32 index = *(u32 *)key;
 255         struct socket *socket;
 256         int err, fd;
 257 
 258         if (map_flags > BPF_EXIST)
 259                 return -EINVAL;
 260 
 261         if (index >= map->max_entries)
 262                 return -E2BIG;
 263 
 264         if (map->value_size == sizeof(u64)) {
 265                 u64 fd64 = *(u64 *)value;
 266 
 267                 if (fd64 > S32_MAX)
 268                         return -EINVAL;
 269                 fd = fd64;
 270         } else {
 271                 fd = *(int *)value;
 272         }
 273 
 274         socket = sockfd_lookup(fd, &err);
 275         if (!socket)
 276                 return err;
 277 
 278         nsk = socket->sk;
 279         if (!nsk) {
 280                 err = -EINVAL;
 281                 goto put_file;
 282         }
 283 
 284         /* Quick checks before taking reuseport_lock */
 285         err = reuseport_array_update_check(array, nsk,
 286                                            rcu_access_pointer(array->ptrs[index]),
 287                                            rcu_access_pointer(nsk->sk_reuseport_cb),
 288                                            map_flags);
 289         if (err)
 290                 goto put_file;
 291 
 292         spin_lock_bh(&reuseport_lock);
 293         /*
 294          * Some of the checks only need reuseport_lock
 295          * but it is done under sk_callback_lock also
 296          * for simplicity reason.
 297          */
 298         write_lock_bh(&nsk->sk_callback_lock);
 299 
 300         osk = rcu_dereference_protected(array->ptrs[index],
 301                                         lockdep_is_held(&reuseport_lock));
 302         reuse = rcu_dereference_protected(nsk->sk_reuseport_cb,
 303                                           lockdep_is_held(&reuseport_lock));
 304         err = reuseport_array_update_check(array, nsk, osk, reuse, map_flags);
 305         if (err)
 306                 goto put_file_unlock;
 307 
 308         /* Ensure reuse->reuseport_id is set */
 309         err = reuseport_get_id(reuse);
 310         if (err < 0)
 311                 goto put_file_unlock;
 312 
 313         WRITE_ONCE(nsk->sk_user_data, &array->ptrs[index]);
 314         rcu_assign_pointer(array->ptrs[index], nsk);
 315         free_osk = osk;
 316         err = 0;
 317 
 318 put_file_unlock:
 319         write_unlock_bh(&nsk->sk_callback_lock);
 320 
 321         if (free_osk) {
 322                 write_lock_bh(&free_osk->sk_callback_lock);
 323                 WRITE_ONCE(free_osk->sk_user_data, NULL);
 324                 write_unlock_bh(&free_osk->sk_callback_lock);
 325         }
 326 
 327         spin_unlock_bh(&reuseport_lock);
 328 put_file:
 329         fput(socket->file);
 330         return err;
 331 }
 332 
 333 /* Called from syscall */
 334 static int reuseport_array_get_next_key(struct bpf_map *map, void *key,
 335                                         void *next_key)
 336 {
 337         struct reuseport_array *array = reuseport_array(map);
 338         u32 index = key ? *(u32 *)key : U32_MAX;
 339         u32 *next = (u32 *)next_key;
 340 
 341         if (index >= array->map.max_entries) {
 342                 *next = 0;
 343                 return 0;
 344         }
 345 
 346         if (index == array->map.max_entries - 1)
 347                 return -ENOENT;
 348 
 349         *next = index + 1;
 350         return 0;
 351 }
 352 
 353 const struct bpf_map_ops reuseport_array_ops = {
 354         .map_alloc_check = reuseport_array_alloc_check,
 355         .map_alloc = reuseport_array_alloc,
 356         .map_free = reuseport_array_free,
 357         .map_lookup_elem = reuseport_array_lookup_elem,
 358         .map_get_next_key = reuseport_array_get_next_key,
 359         .map_delete_elem = reuseport_array_delete_elem,
 360 };