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