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Linux/net/core/sock_reuseport.c

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  1 /*
  2  * To speed up listener socket lookup, create an array to store all sockets
  3  * listening on the same port.  This allows a decision to be made after finding
  4  * the first socket.  An optional BPF program can also be configured for
  5  * selecting the socket index from the array of available sockets.
  6  */
  7 
  8 #include <net/sock_reuseport.h>
  9 #include <linux/bpf.h>
 10 #include <linux/rcupdate.h>
 11 
 12 #define INIT_SOCKS 128
 13 
 14 static DEFINE_SPINLOCK(reuseport_lock);
 15 
 16 static struct sock_reuseport *__reuseport_alloc(u16 max_socks)
 17 {
 18         size_t size = sizeof(struct sock_reuseport) +
 19                       sizeof(struct sock *) * max_socks;
 20         struct sock_reuseport *reuse = kzalloc(size, GFP_ATOMIC);
 21 
 22         if (!reuse)
 23                 return NULL;
 24 
 25         reuse->max_socks = max_socks;
 26 
 27         RCU_INIT_POINTER(reuse->prog, NULL);
 28         return reuse;
 29 }
 30 
 31 int reuseport_alloc(struct sock *sk)
 32 {
 33         struct sock_reuseport *reuse;
 34 
 35         /* bh lock used since this function call may precede hlist lock in
 36          * soft irq of receive path or setsockopt from process context
 37          */
 38         spin_lock_bh(&reuseport_lock);
 39         WARN_ONCE(rcu_dereference_protected(sk->sk_reuseport_cb,
 40                                             lockdep_is_held(&reuseport_lock)),
 41                   "multiple allocations for the same socket");
 42         reuse = __reuseport_alloc(INIT_SOCKS);
 43         if (!reuse) {
 44                 spin_unlock_bh(&reuseport_lock);
 45                 return -ENOMEM;
 46         }
 47 
 48         reuse->socks[0] = sk;
 49         reuse->num_socks = 1;
 50         rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
 51 
 52         spin_unlock_bh(&reuseport_lock);
 53 
 54         return 0;
 55 }
 56 EXPORT_SYMBOL(reuseport_alloc);
 57 
 58 static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse)
 59 {
 60         struct sock_reuseport *more_reuse;
 61         u32 more_socks_size, i;
 62 
 63         more_socks_size = reuse->max_socks * 2U;
 64         if (more_socks_size > U16_MAX)
 65                 return NULL;
 66 
 67         more_reuse = __reuseport_alloc(more_socks_size);
 68         if (!more_reuse)
 69                 return NULL;
 70 
 71         more_reuse->max_socks = more_socks_size;
 72         more_reuse->num_socks = reuse->num_socks;
 73         more_reuse->prog = reuse->prog;
 74 
 75         memcpy(more_reuse->socks, reuse->socks,
 76                reuse->num_socks * sizeof(struct sock *));
 77 
 78         for (i = 0; i < reuse->num_socks; ++i)
 79                 rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
 80                                    more_reuse);
 81 
 82         /* Note: we use kfree_rcu here instead of reuseport_free_rcu so
 83          * that reuse and more_reuse can temporarily share a reference
 84          * to prog.
 85          */
 86         kfree_rcu(reuse, rcu);
 87         return more_reuse;
 88 }
 89 
 90 /**
 91  *  reuseport_add_sock - Add a socket to the reuseport group of another.
 92  *  @sk:  New socket to add to the group.
 93  *  @sk2: Socket belonging to the existing reuseport group.
 94  *  May return ENOMEM and not add socket to group under memory pressure.
 95  */
 96 int reuseport_add_sock(struct sock *sk, struct sock *sk2)
 97 {
 98         struct sock_reuseport *reuse;
 99 
100         if (!rcu_access_pointer(sk2->sk_reuseport_cb)) {
101                 int err = reuseport_alloc(sk2);
102 
103                 if (err)
104                         return err;
105         }
106 
107         spin_lock_bh(&reuseport_lock);
108         reuse = rcu_dereference_protected(sk2->sk_reuseport_cb,
109                                           lockdep_is_held(&reuseport_lock)),
110         WARN_ONCE(rcu_dereference_protected(sk->sk_reuseport_cb,
111                                             lockdep_is_held(&reuseport_lock)),
112                   "socket already in reuseport group");
113 
114         if (reuse->num_socks == reuse->max_socks) {
115                 reuse = reuseport_grow(reuse);
116                 if (!reuse) {
117                         spin_unlock_bh(&reuseport_lock);
118                         return -ENOMEM;
119                 }
120         }
121 
122         reuse->socks[reuse->num_socks] = sk;
123         /* paired with smp_rmb() in reuseport_select_sock() */
124         smp_wmb();
125         reuse->num_socks++;
126         rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
127 
128         spin_unlock_bh(&reuseport_lock);
129 
130         return 0;
131 }
132 
133 static void reuseport_free_rcu(struct rcu_head *head)
134 {
135         struct sock_reuseport *reuse;
136 
137         reuse = container_of(head, struct sock_reuseport, rcu);
138         if (reuse->prog)
139                 bpf_prog_destroy(reuse->prog);
140         kfree(reuse);
141 }
142 
143 void reuseport_detach_sock(struct sock *sk)
144 {
145         struct sock_reuseport *reuse;
146         int i;
147 
148         spin_lock_bh(&reuseport_lock);
149         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
150                                           lockdep_is_held(&reuseport_lock));
151         rcu_assign_pointer(sk->sk_reuseport_cb, NULL);
152 
153         for (i = 0; i < reuse->num_socks; i++) {
154                 if (reuse->socks[i] == sk) {
155                         reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
156                         reuse->num_socks--;
157                         if (reuse->num_socks == 0)
158                                 call_rcu(&reuse->rcu, reuseport_free_rcu);
159                         break;
160                 }
161         }
162         spin_unlock_bh(&reuseport_lock);
163 }
164 EXPORT_SYMBOL(reuseport_detach_sock);
165 
166 static struct sock *run_bpf(struct sock_reuseport *reuse, u16 socks,
167                             struct bpf_prog *prog, struct sk_buff *skb,
168                             int hdr_len)
169 {
170         struct sk_buff *nskb = NULL;
171         u32 index;
172 
173         if (skb_shared(skb)) {
174                 nskb = skb_clone(skb, GFP_ATOMIC);
175                 if (!nskb)
176                         return NULL;
177                 skb = nskb;
178         }
179 
180         /* temporarily advance data past protocol header */
181         if (!pskb_pull(skb, hdr_len)) {
182                 kfree_skb(nskb);
183                 return NULL;
184         }
185         index = bpf_prog_run_save_cb(prog, skb);
186         __skb_push(skb, hdr_len);
187 
188         consume_skb(nskb);
189 
190         if (index >= socks)
191                 return NULL;
192 
193         return reuse->socks[index];
194 }
195 
196 /**
197  *  reuseport_select_sock - Select a socket from an SO_REUSEPORT group.
198  *  @sk: First socket in the group.
199  *  @hash: When no BPF filter is available, use this hash to select.
200  *  @skb: skb to run through BPF filter.
201  *  @hdr_len: BPF filter expects skb data pointer at payload data.  If
202  *    the skb does not yet point at the payload, this parameter represents
203  *    how far the pointer needs to advance to reach the payload.
204  *  Returns a socket that should receive the packet (or NULL on error).
205  */
206 struct sock *reuseport_select_sock(struct sock *sk,
207                                    u32 hash,
208                                    struct sk_buff *skb,
209                                    int hdr_len)
210 {
211         struct sock_reuseport *reuse;
212         struct bpf_prog *prog;
213         struct sock *sk2 = NULL;
214         u16 socks;
215 
216         rcu_read_lock();
217         reuse = rcu_dereference(sk->sk_reuseport_cb);
218 
219         /* if memory allocation failed or add call is not yet complete */
220         if (!reuse)
221                 goto out;
222 
223         prog = rcu_dereference(reuse->prog);
224         socks = READ_ONCE(reuse->num_socks);
225         if (likely(socks)) {
226                 /* paired with smp_wmb() in reuseport_add_sock() */
227                 smp_rmb();
228 
229                 if (prog && skb)
230                         sk2 = run_bpf(reuse, socks, prog, skb, hdr_len);
231                 else
232                         sk2 = reuse->socks[reciprocal_scale(hash, socks)];
233         }
234 
235 out:
236         rcu_read_unlock();
237         return sk2;
238 }
239 EXPORT_SYMBOL(reuseport_select_sock);
240 
241 struct bpf_prog *
242 reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog)
243 {
244         struct sock_reuseport *reuse;
245         struct bpf_prog *old_prog;
246 
247         spin_lock_bh(&reuseport_lock);
248         reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
249                                           lockdep_is_held(&reuseport_lock));
250         old_prog = rcu_dereference_protected(reuse->prog,
251                                              lockdep_is_held(&reuseport_lock));
252         rcu_assign_pointer(reuse->prog, prog);
253         spin_unlock_bh(&reuseport_lock);
254 
255         return old_prog;
256 }
257 EXPORT_SYMBOL(reuseport_attach_prog);
258 

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