net/core/sock_reuseport.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * To speed up listener socket lookup, create an array to store all sockets
   4  * listening on the same port.  This allows a decision to be made after finding
   5  * the first socket.  An optional BPF program can also be configured for
   6  * selecting the socket index from the array of available sockets.
   7  */
   8
   9 #include <net/sock_reuseport.h>
  10 #include <linux/bpf.h>
  11 #include <linux/idr.h>
  12 #include <linux/filter.h>
  13 #include <linux/rcupdate.h>
  14
  15 #define INIT_SOCKS 128
  16
  17 DEFINE_SPINLOCK(reuseport_lock);
  18
  19 #define REUSEPORT_MIN_ID 1
  20 static DEFINE_IDA(reuseport_ida);
  21
  22 int reuseport_get_id(struct sock_reuseport *reuse)
  23 {
  24         int id;
  25
  26         if (reuse->reuseport_id)
  27                 return reuse->reuseport_id;
  28
  29         id = ida_simple_get(&reuseport_ida, REUSEPORT_MIN_ID, 0,
  30                             /* Called under reuseport_lock */
  31                             GFP_ATOMIC);
  32         if (id < 0)
  33                 return id;
  34
  35         reuse->reuseport_id = id;
  36
  37         return reuse->reuseport_id;
  38 }
  39
  40 static struct sock_reuseport *__reuseport_alloc(unsigned int max_socks)
  41 {
  42         unsigned int size = sizeof(struct sock_reuseport) +
  43                       sizeof(struct sock *) * max_socks;
  44         struct sock_reuseport *reuse = kzalloc(size, GFP_ATOMIC);
  45
  46         if (!reuse)
  47                 return NULL;
  48
  49         reuse->max_socks = max_socks;
  50
  51         RCU_INIT_POINTER(reuse->prog, NULL);
  52         return reuse;
  53 }
  54
  55 int reuseport_alloc(struct sock *sk, bool bind_inany)
  56 {
  57         struct sock_reuseport *reuse;
  58
  59         /* bh lock used since this function call may precede hlist lock in
  60          * soft irq of receive path or setsockopt from process context
  61          */
  62         spin_lock_bh(&reuseport_lock);
  63
  64         /* Allocation attempts can occur concurrently via the setsockopt path
  65          * and the bind/hash path.  Nothing to do when we lose the race.
  66          */
  67         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
  68                                           lockdep_is_held(&reuseport_lock));
  69         if (reuse) {
  70                 /* Only set reuse->bind_inany if the bind_inany is true.
  71                  * Otherwise, it will overwrite the reuse->bind_inany
  72                  * which was set by the bind/hash path.
  73                  */
  74                 if (bind_inany)
  75                         reuse->bind_inany = bind_inany;
  76                 goto out;
  77         }
  78
  79         reuse = __reuseport_alloc(INIT_SOCKS);
  80         if (!reuse) {
  81                 spin_unlock_bh(&reuseport_lock);
  82                 return -ENOMEM;
  83         }
  84
  85         reuse->socks[0] = sk;
  86         reuse->num_socks = 1;
  87         reuse->bind_inany = bind_inany;
  88         rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
  89
  90 out:
  91         spin_unlock_bh(&reuseport_lock);
  92
  93         return 0;
  94 }
  95 EXPORT_SYMBOL(reuseport_alloc);
  96
  97 static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse)
  98 {
  99         struct sock_reuseport *more_reuse;
 100         u32 more_socks_size, i;
 101
 102         more_socks_size = reuse->max_socks * 2U;
 103         if (more_socks_size > U16_MAX)
 104                 return NULL;
 105
 106         more_reuse = __reuseport_alloc(more_socks_size);
 107         if (!more_reuse)
 108                 return NULL;
 109
 110         more_reuse->num_socks = reuse->num_socks;
 111         more_reuse->prog = reuse->prog;
 112         more_reuse->reuseport_id = reuse->reuseport_id;
 113         more_reuse->bind_inany = reuse->bind_inany;
 114
 115         memcpy(more_reuse->socks, reuse->socks,
 116                reuse->num_socks * sizeof(struct sock *));
 117         more_reuse->synq_overflow_ts = READ_ONCE(reuse->synq_overflow_ts);
 118
 119         for (i = 0; i < reuse->num_socks; ++i)
 120                 rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
 121                                    more_reuse);
 122
 123         /* Note: we use kfree_rcu here instead of reuseport_free_rcu so
 124          * that reuse and more_reuse can temporarily share a reference
 125          * to prog.
 126          */
 127         kfree_rcu(reuse, rcu);
 128         return more_reuse;
 129 }
 130
 131 static void reuseport_free_rcu(struct rcu_head *head)
 132 {
 133         struct sock_reuseport *reuse;
 134
 135         reuse = container_of(head, struct sock_reuseport, rcu);
 136         sk_reuseport_prog_free(rcu_dereference_protected(reuse->prog, 1));
 137         if (reuse->reuseport_id)
 138                 ida_simple_remove(&reuseport_ida, reuse->reuseport_id);
 139         kfree(reuse);
 140 }
 141
 142 /**
 143  *  reuseport_add_sock - Add a socket to the reuseport group of another.
 144  *  @sk:  New socket to add to the group.
 145  *  @sk2: Socket belonging to the existing reuseport group.
 146  *  @bind_inany: Whether or not the group is bound to a local INANY address.
 147  *
 148  *  May return ENOMEM and not add socket to group under memory pressure.
 149  */
 150 int reuseport_add_sock(struct sock *sk, struct sock *sk2, bool bind_inany)
 151 {
 152         struct sock_reuseport *old_reuse, *reuse;
 153
 154         if (!rcu_access_pointer(sk2->sk_reuseport_cb)) {
 155                 int err = reuseport_alloc(sk2, bind_inany);
 156
 157                 if (err)
 158                         return err;
 159         }
 160
 161         spin_lock_bh(&reuseport_lock);
 162         reuse = rcu_dereference_protected(sk2->sk_reuseport_cb,
 163                                           lockdep_is_held(&reuseport_lock));
 164         old_reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
 165                                              lockdep_is_held(&reuseport_lock));
 166         if (old_reuse && old_reuse->num_socks != 1) {
 167                 spin_unlock_bh(&reuseport_lock);
 168                 return -EBUSY;
 169         }
 170
 171         if (reuse->num_socks == reuse->max_socks) {
 172                 reuse = reuseport_grow(reuse);
 173                 if (!reuse) {
 174                         spin_unlock_bh(&reuseport_lock);
 175                         return -ENOMEM;
 176                 }
 177         }
 178
 179         reuse->socks[reuse->num_socks] = sk;
 180         /* paired with smp_rmb() in reuseport_select_sock() */
 181         smp_wmb();
 182         reuse->num_socks++;
 183         rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
 184
 185         spin_unlock_bh(&reuseport_lock);
 186
 187         if (old_reuse)
 188                 call_rcu(&old_reuse->rcu, reuseport_free_rcu);
 189         return 0;
 190 }
 191 EXPORT_SYMBOL(reuseport_add_sock);
 192
 193 void reuseport_detach_sock(struct sock *sk)
 194 {
 195         struct sock_reuseport *reuse;
 196         int i;
 197
 198         spin_lock_bh(&reuseport_lock);
 199         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
 200                                           lockdep_is_held(&reuseport_lock));
 201
 202         /* At least one of the sk in this reuseport group is added to
 203          * a bpf map.  Notify the bpf side.  The bpf map logic will
 204          * remove the sk if it is indeed added to a bpf map.
 205          */
 206         if (reuse->reuseport_id)
 207                 bpf_sk_reuseport_detach(sk);
 208
 209         rcu_assign_pointer(sk->sk_reuseport_cb, NULL);
 210
 211         for (i = 0; i < reuse->num_socks; i++) {
 212                 if (reuse->socks[i] == sk) {
 213                         reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
 214                         reuse->num_socks--;
 215                         if (reuse->num_socks == 0)
 216                                 call_rcu(&reuse->rcu, reuseport_free_rcu);
 217                         break;
 218                 }
 219         }
 220         spin_unlock_bh(&reuseport_lock);
 221 }
 222 EXPORT_SYMBOL(reuseport_detach_sock);
 223
 224 static struct sock *run_bpf_filter(struct sock_reuseport *reuse, u16 socks,
 225                                    struct bpf_prog *prog, struct sk_buff *skb,
 226                                    int hdr_len)
 227 {
 228         struct sk_buff *nskb = NULL;
 229         u32 index;
 230
 231         if (skb_shared(skb)) {
 232                 nskb = skb_clone(skb, GFP_ATOMIC);
 233                 if (!nskb)
 234                         return NULL;
 235                 skb = nskb;
 236         }
 237
 238         /* temporarily advance data past protocol header */
 239         if (!pskb_pull(skb, hdr_len)) {
 240                 kfree_skb(nskb);
 241                 return NULL;
 242         }
 243         index = bpf_prog_run_save_cb(prog, skb);
 244         __skb_push(skb, hdr_len);
 245
 246         consume_skb(nskb);
 247
 248         if (index >= socks)
 249                 return NULL;
 250
 251         return reuse->socks[index];
 252 }
 253
 254 /**
 255  *  reuseport_select_sock - Select a socket from an SO_REUSEPORT group.
 256  *  @sk: First socket in the group.
 257  *  @hash: When no BPF filter is available, use this hash to select.
 258  *  @skb: skb to run through BPF filter.
 259  *  @hdr_len: BPF filter expects skb data pointer at payload data.  If
 260  *    the skb does not yet point at the payload, this parameter represents
 261  *    how far the pointer needs to advance to reach the payload.
 262  *  Returns a socket that should receive the packet (or NULL on error).
 263  */
 264 struct sock *reuseport_select_sock(struct sock *sk,
 265                                    u32 hash,
 266                                    struct sk_buff *skb,
 267                                    int hdr_len)
 268 {
 269         struct sock_reuseport *reuse;
 270         struct bpf_prog *prog;
 271         struct sock *sk2 = NULL;
 272         u16 socks;
 273
 274         rcu_read_lock();
 275         reuse = rcu_dereference(sk->sk_reuseport_cb);
 276
 277         /* if memory allocation failed or add call is not yet complete */
 278         if (!reuse)
 279                 goto out;
 280
 281         prog = rcu_dereference(reuse->prog);
 282         socks = READ_ONCE(reuse->num_socks);
 283         if (likely(socks)) {
 284                 /* paired with smp_wmb() in reuseport_add_sock() */
 285                 smp_rmb();
 286
 287                 if (!prog || !skb)
 288                         goto select_by_hash;
 289
 290                 if (prog->type == BPF_PROG_TYPE_SK_REUSEPORT)
 291                         sk2 = bpf_run_sk_reuseport(reuse, sk, prog, skb, hash);
 292                 else
 293                         sk2 = run_bpf_filter(reuse, socks, prog, skb, hdr_len);
 294
 295 select_by_hash:
 296                 /* no bpf or invalid bpf result: fall back to hash usage */
 297                 if (!sk2) {
 298                         int i, j;
 299
 300                         i = j = reciprocal_scale(hash, socks);
 301                         while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {
 302                                 i++;
 303                                 if (i >= reuse->num_socks)
 304                                         i = 0;
 305                                 if (i == j)
 306                                         goto out;
 307                         }
 308                         sk2 = reuse->socks[i];
 309                 }
 310         }
 311
 312 out:
 313         rcu_read_unlock();
 314         return sk2;
 315 }
 316 EXPORT_SYMBOL(reuseport_select_sock);
 317
 318 int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog)
 319 {
 320         struct sock_reuseport *reuse;
 321         struct bpf_prog *old_prog;
 322
 323         if (sk_unhashed(sk) && sk->sk_reuseport) {
 324                 int err = reuseport_alloc(sk, false);
 325
 326                 if (err)
 327                         return err;
 328         } else if (!rcu_access_pointer(sk->sk_reuseport_cb)) {
 329                 /* The socket wasn't bound with SO_REUSEPORT */
 330                 return -EINVAL;
 331         }
 332
 333         spin_lock_bh(&reuseport_lock);
 334         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
 335                                           lockdep_is_held(&reuseport_lock));
 336         old_prog = rcu_dereference_protected(reuse->prog,
 337                                              lockdep_is_held(&reuseport_lock));
 338         rcu_assign_pointer(reuse->prog, prog);
 339         spin_unlock_bh(&reuseport_lock);
 340
 341         sk_reuseport_prog_free(old_prog);
 342         return 0;
 343 }
 344 EXPORT_SYMBOL(reuseport_attach_prog);
 345
 346 int reuseport_detach_prog(struct sock *sk)
 347 {
 348         struct sock_reuseport *reuse;
 349         struct bpf_prog *old_prog;
 350
 351         if (!rcu_access_pointer(sk->sk_reuseport_cb))
 352                 return sk->sk_reuseport ? -ENOENT : -EINVAL;
 353
 354         old_prog = NULL;
 355         spin_lock_bh(&reuseport_lock);
 356         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
 357                                           lockdep_is_held(&reuseport_lock));
 358         old_prog = rcu_replace_pointer(reuse->prog, old_prog,
 359                                        lockdep_is_held(&reuseport_lock));
 360         spin_unlock_bh(&reuseport_lock);
 361
 362         if (!old_prog)
 363                 return -ENOENT;
 364
 365         sk_reuseport_prog_free(old_prog);
 366         return 0;
 367 }
 368 EXPORT_SYMBOL(reuseport_detach_prog);