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/rcupdate.h>
  12
  13 #define INIT_SOCKS 128
  14
  15 static DEFINE_SPINLOCK(reuseport_lock);
  16
  17 static struct sock_reuseport *__reuseport_alloc(unsigned int max_socks)
  18 {
  19         unsigned int size = sizeof(struct sock_reuseport) +
  20                       sizeof(struct sock *) * max_socks;
  21         struct sock_reuseport *reuse = kzalloc(size, GFP_ATOMIC);
  22
  23         if (!reuse)
  24                 return NULL;
  25
  26         reuse->max_socks = max_socks;
  27
  28         RCU_INIT_POINTER(reuse->prog, NULL);
  29         return reuse;
  30 }
  31
  32 int reuseport_alloc(struct sock *sk)
  33 {
  34         struct sock_reuseport *reuse;
  35
  36         /* bh lock used since this function call may precede hlist lock in
  37          * soft irq of receive path or setsockopt from process context
  38          */
  39         spin_lock_bh(&reuseport_lock);
  40
  41         /* Allocation attempts can occur concurrently via the setsockopt path
  42          * and the bind/hash path.  Nothing to do when we lose the race.
  43          */
  44         if (rcu_dereference_protected(sk->sk_reuseport_cb,
  45                                       lockdep_is_held(&reuseport_lock)))
  46                 goto out;
  47
  48         reuse = __reuseport_alloc(INIT_SOCKS);
  49         if (!reuse) {
  50                 spin_unlock_bh(&reuseport_lock);
  51                 return -ENOMEM;
  52         }
  53
  54         reuse->socks[0] = sk;
  55         reuse->num_socks = 1;
  56         rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
  57
  58 out:
  59         spin_unlock_bh(&reuseport_lock);
  60
  61         return 0;
  62 }
  63 EXPORT_SYMBOL(reuseport_alloc);
  64
  65 static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse)
  66 {
  67         struct sock_reuseport *more_reuse;
  68         u32 more_socks_size, i;
  69
  70         more_socks_size = reuse->max_socks * 2U;
  71         if (more_socks_size > U16_MAX)
  72                 return NULL;
  73
  74         more_reuse = __reuseport_alloc(more_socks_size);
  75         if (!more_reuse)
  76                 return NULL;
  77
  78         more_reuse->max_socks = more_socks_size;
  79         more_reuse->num_socks = reuse->num_socks;
  80         more_reuse->prog = reuse->prog;
  81
  82         memcpy(more_reuse->socks, reuse->socks,
  83                reuse->num_socks * sizeof(struct sock *));
  84
  85         for (i = 0; i < reuse->num_socks; ++i)
  86                 rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
  87                                    more_reuse);
  88
  89         /* Note: we use kfree_rcu here instead of reuseport_free_rcu so
  90          * that reuse and more_reuse can temporarily share a reference
  91          * to prog.
  92          */
  93         kfree_rcu(reuse, rcu);
  94         return more_reuse;
  95 }
  96
  97 /**
  98  *  reuseport_add_sock - Add a socket to the reuseport group of another.
  99  *  @sk:  New socket to add to the group.
 100  *  @sk2: Socket belonging to the existing reuseport group.
 101  *  May return ENOMEM and not add socket to group under memory pressure.
 102  */
 103 int reuseport_add_sock(struct sock *sk, struct sock *sk2)
 104 {
 105         struct sock_reuseport *reuse;
 106
 107         if (!rcu_access_pointer(sk2->sk_reuseport_cb)) {
 108                 int err = reuseport_alloc(sk2);
 109
 110                 if (err)
 111                         return err;
 112         }
 113
 114         spin_lock_bh(&reuseport_lock);
 115         reuse = rcu_dereference_protected(sk2->sk_reuseport_cb,
 116                                           lockdep_is_held(&reuseport_lock)),
 117         WARN_ONCE(rcu_dereference_protected(sk->sk_reuseport_cb,
 118                                             lockdep_is_held(&reuseport_lock)),
 119                   "socket already in reuseport group");
 120
 121         if (reuse->num_socks == reuse->max_socks) {
 122                 reuse = reuseport_grow(reuse);
 123                 if (!reuse) {
 124                         spin_unlock_bh(&reuseport_lock);
 125                         return -ENOMEM;
 126                 }
 127         }
 128
 129         reuse->socks[reuse->num_socks] = sk;
 130         /* paired with smp_rmb() in reuseport_select_sock() */
 131         smp_wmb();
 132         reuse->num_socks++;
 133         rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
 134
 135         spin_unlock_bh(&reuseport_lock);
 136
 137         return 0;
 138 }
 139
 140 static void reuseport_free_rcu(struct rcu_head *head)
 141 {
 142         struct sock_reuseport *reuse;
 143
 144         reuse = container_of(head, struct sock_reuseport, rcu);
 145         if (reuse->prog)
 146                 bpf_prog_destroy(reuse->prog);
 147         kfree(reuse);
 148 }
 149
 150 void reuseport_detach_sock(struct sock *sk)
 151 {
 152         struct sock_reuseport *reuse;
 153         int i;
 154
 155         spin_lock_bh(&reuseport_lock);
 156         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
 157                                           lockdep_is_held(&reuseport_lock));
 158         rcu_assign_pointer(sk->sk_reuseport_cb, NULL);
 159
 160         for (i = 0; i < reuse->num_socks; i++) {
 161                 if (reuse->socks[i] == sk) {
 162                         reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
 163                         reuse->num_socks--;
 164                         if (reuse->num_socks == 0)
 165                                 call_rcu(&reuse->rcu, reuseport_free_rcu);
 166                         break;
 167                 }
 168         }
 169         spin_unlock_bh(&reuseport_lock);
 170 }
 171 EXPORT_SYMBOL(reuseport_detach_sock);
 172
 173 static struct sock *run_bpf(struct sock_reuseport *reuse, u16 socks,
 174                             struct bpf_prog *prog, struct sk_buff *skb,
 175                             int hdr_len)
 176 {
 177         struct sk_buff *nskb = NULL;
 178         u32 index;
 179
 180         if (skb_shared(skb)) {
 181                 nskb = skb_clone(skb, GFP_ATOMIC);
 182                 if (!nskb)
 183                         return NULL;
 184                 skb = nskb;
 185         }
 186
 187         /* temporarily advance data past protocol header */
 188         if (!pskb_pull(skb, hdr_len)) {
 189                 kfree_skb(nskb);
 190                 return NULL;
 191         }
 192         index = bpf_prog_run_save_cb(prog, skb);
 193         __skb_push(skb, hdr_len);
 194
 195         consume_skb(nskb);
 196
 197         if (index >= socks)
 198                 return NULL;
 199
 200         return reuse->socks[index];
 201 }
 202
 203 /**
 204  *  reuseport_select_sock - Select a socket from an SO_REUSEPORT group.
 205  *  @sk: First socket in the group.
 206  *  @hash: When no BPF filter is available, use this hash to select.
 207  *  @skb: skb to run through BPF filter.
 208  *  @hdr_len: BPF filter expects skb data pointer at payload data.  If
 209  *    the skb does not yet point at the payload, this parameter represents
 210  *    how far the pointer needs to advance to reach the payload.
 211  *  Returns a socket that should receive the packet (or NULL on error).
 212  */
 213 struct sock *reuseport_select_sock(struct sock *sk,
 214                                    u32 hash,
 215                                    struct sk_buff *skb,
 216                                    int hdr_len)
 217 {
 218         struct sock_reuseport *reuse;
 219         struct bpf_prog *prog;
 220         struct sock *sk2 = NULL;
 221         u16 socks;
 222
 223         rcu_read_lock();
 224         reuse = rcu_dereference(sk->sk_reuseport_cb);
 225
 226         /* if memory allocation failed or add call is not yet complete */
 227         if (!reuse)
 228                 goto out;
 229
 230         prog = rcu_dereference(reuse->prog);
 231         socks = READ_ONCE(reuse->num_socks);
 232         if (likely(socks)) {
 233                 /* paired with smp_wmb() in reuseport_add_sock() */
 234                 smp_rmb();
 235
 236                 if (prog && skb)
 237                         sk2 = run_bpf(reuse, socks, prog, skb, hdr_len);
 238                 else
 239                         sk2 = reuse->socks[reciprocal_scale(hash, socks)];
 240         }
 241
 242 out:
 243         rcu_read_unlock();
 244         return sk2;
 245 }
 246 EXPORT_SYMBOL(reuseport_select_sock);
 247
 248 struct bpf_prog *
 249 reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog)
 250 {
 251         struct sock_reuseport *reuse;
 252         struct bpf_prog *old_prog;
 253
 254         spin_lock_bh(&reuseport_lock);
 255         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
 256                                           lockdep_is_held(&reuseport_lock));
 257         old_prog = rcu_dereference_protected(reuse->prog,
 258                                              lockdep_is_held(&reuseport_lock));
 259         rcu_assign_pointer(reuse->prog, prog);
 260         spin_unlock_bh(&reuseport_lock);
 261
 262         return old_prog;
 263 }
 264 EXPORT_SYMBOL(reuseport_attach_prog);