xref: /linux/kernel/bpf/reuseport_array.c (revision db10cb9b) 
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 #include <linux/btf_ids.h>
10 
11 struct reuseport_array {
12 	struct bpf_map map;
13 	struct sock __rcu *ptrs[];
14 };
15 
16 static struct reuseport_array *reuseport_array(struct bpf_map *map)
17 {
18 	return (struct reuseport_array *)map;
19 }
20 
21 /* The caller must hold the reuseport_lock */
22 void bpf_sk_reuseport_detach(struct sock *sk)
23 {
24 	struct sock __rcu **socks;
25 
26 	write_lock_bh(&sk->sk_callback_lock);
27 	socks = __locked_read_sk_user_data_with_flags(sk, SK_USER_DATA_BPF);
28 	if (socks) {
29 		WRITE_ONCE(sk->sk_user_data, NULL);
30 		/*
31 		 * Do not move this NULL assignment outside of
32 		 * sk->sk_callback_lock because there is
33 		 * a race with reuseport_array_free()
34 		 * which does not hold the reuseport_lock.
35 		 */
36 		RCU_INIT_POINTER(*socks, NULL);
37 	}
38 	write_unlock_bh(&sk->sk_callback_lock);
39 }
40 
41 static int reuseport_array_alloc_check(union bpf_attr *attr)
42 {
43 	if (attr->value_size != sizeof(u32) &&
44 	    attr->value_size != sizeof(u64))
45 		return -EINVAL;
46 
47 	return array_map_alloc_check(attr);
48 }
49 
50 static void *reuseport_array_lookup_elem(struct bpf_map *map, void *key)
51 {
52 	struct reuseport_array *array = reuseport_array(map);
53 	u32 index = *(u32 *)key;
54 
55 	if (unlikely(index >= array->map.max_entries))
56 		return NULL;
57 
58 	return rcu_dereference(array->ptrs[index]);
59 }
60 
61 /* Called from syscall only */
62 static long reuseport_array_delete_elem(struct bpf_map *map, void *key)
63 {
64 	struct reuseport_array *array = reuseport_array(map);
65 	u32 index = *(u32 *)key;
66 	struct sock *sk;
67 	int err;
68 
69 	if (index >= map->max_entries)
70 		return -E2BIG;
71 
72 	if (!rcu_access_pointer(array->ptrs[index]))
73 		return -ENOENT;
74 
75 	spin_lock_bh(&reuseport_lock);
76 
77 	sk = rcu_dereference_protected(array->ptrs[index],
78 				       lockdep_is_held(&reuseport_lock));
79 	if (sk) {
80 		write_lock_bh(&sk->sk_callback_lock);
81 		WRITE_ONCE(sk->sk_user_data, NULL);
82 		RCU_INIT_POINTER(array->ptrs[index], NULL);
83 		write_unlock_bh(&sk->sk_callback_lock);
84 		err = 0;
85 	} else {
86 		err = -ENOENT;
87 	}
88 
89 	spin_unlock_bh(&reuseport_lock);
90 
91 	return err;
92 }
93 
94 static void reuseport_array_free(struct bpf_map *map)
95 {
96 	struct reuseport_array *array = reuseport_array(map);
97 	struct sock *sk;
98 	u32 i;
99 
100 	/*
101 	 * ops->map_*_elem() will not be able to access this
102 	 * array now. Hence, this function only races with
103 	 * bpf_sk_reuseport_detach() which was triggered by
104 	 * close() or disconnect().
105 	 *
106 	 * This function and bpf_sk_reuseport_detach() are
107 	 * both removing sk from "array".  Who removes it
108 	 * first does not matter.
109 	 *
110 	 * The only concern here is bpf_sk_reuseport_detach()
111 	 * may access "array" which is being freed here.
112 	 * bpf_sk_reuseport_detach() access this "array"
113 	 * through sk->sk_user_data _and_ with sk->sk_callback_lock
114 	 * held which is enough because this "array" is not freed
115 	 * until all sk->sk_user_data has stopped referencing this "array".
116 	 *
117 	 * Hence, due to the above, taking "reuseport_lock" is not
118 	 * needed here.
119 	 */
120 
121 	/*
122 	 * Since reuseport_lock is not taken, sk is accessed under
123 	 * rcu_read_lock()
124 	 */
125 	rcu_read_lock();
126 	for (i = 0; i < map->max_entries; i++) {
127 		sk = rcu_dereference(array->ptrs[i]);
128 		if (sk) {
129 			write_lock_bh(&sk->sk_callback_lock);
130 			/*
131 			 * No need for WRITE_ONCE(). At this point,
132 			 * no one is reading it without taking the
133 			 * sk->sk_callback_lock.
134 			 */
135 			sk->sk_user_data = NULL;
136 			write_unlock_bh(&sk->sk_callback_lock);
137 			RCU_INIT_POINTER(array->ptrs[i], NULL);
138 		}
139 	}
140 	rcu_read_unlock();
141 
142 	/*
143 	 * Once reaching here, all sk->sk_user_data is not
144 	 * referencing this "array". "array" can be freed now.
145 	 */
146 	bpf_map_area_free(array);
147 }
148 
149 static struct bpf_map *reuseport_array_alloc(union bpf_attr *attr)
150 {
151 	int numa_node = bpf_map_attr_numa_node(attr);
152 	struct reuseport_array *array;
153 
154 	/* allocate all map elements and zero-initialize them */
155 	array = bpf_map_area_alloc(struct_size(array, ptrs, attr->max_entries), numa_node);
156 	if (!array)
157 		return ERR_PTR(-ENOMEM);
158 
159 	/* copy mandatory map attributes */
160 	bpf_map_init_from_attr(&array->map, attr);
161 
162 	return &array->map;
163 }
164 
165 int bpf_fd_reuseport_array_lookup_elem(struct bpf_map *map, void *key,
166 				       void *value)
167 {
168 	struct sock *sk;
169 	int err;
170 
171 	if (map->value_size != sizeof(u64))
172 		return -ENOSPC;
173 
174 	rcu_read_lock();
175 	sk = reuseport_array_lookup_elem(map, key);
176 	if (sk) {
177 		*(u64 *)value = __sock_gen_cookie(sk);
178 		err = 0;
179 	} else {
180 		err = -ENOENT;
181 	}
182 	rcu_read_unlock();
183 
184 	return err;
185 }
186 
187 static int
188 reuseport_array_update_check(const struct reuseport_array *array,
189 			     const struct sock *nsk,
190 			     const struct sock *osk,
191 			     const struct sock_reuseport *nsk_reuse,
192 			     u32 map_flags)
193 {
194 	if (osk && map_flags == BPF_NOEXIST)
195 		return -EEXIST;
196 
197 	if (!osk && map_flags == BPF_EXIST)
198 		return -ENOENT;
199 
200 	if (nsk->sk_protocol != IPPROTO_UDP && nsk->sk_protocol != IPPROTO_TCP)
201 		return -ENOTSUPP;
202 
203 	if (nsk->sk_family != AF_INET && nsk->sk_family != AF_INET6)
204 		return -ENOTSUPP;
205 
206 	if (nsk->sk_type != SOCK_STREAM && nsk->sk_type != SOCK_DGRAM)
207 		return -ENOTSUPP;
208 
209 	/*
210 	 * sk must be hashed (i.e. listening in the TCP case or binded
211 	 * in the UDP case) and
212 	 * it must also be a SO_REUSEPORT sk (i.e. reuse cannot be NULL).
213 	 *
214 	 * Also, sk will be used in bpf helper that is protected by
215 	 * rcu_read_lock().
216 	 */
217 	if (!sock_flag(nsk, SOCK_RCU_FREE) || !sk_hashed(nsk) || !nsk_reuse)
218 		return -EINVAL;
219 
220 	/* READ_ONCE because the sk->sk_callback_lock may not be held here */
221 	if (READ_ONCE(nsk->sk_user_data))
222 		return -EBUSY;
223 
224 	return 0;
225 }
226 
227 /*
228  * Called from syscall only.
229  * The "nsk" in the fd refcnt.
230  * The "osk" and "reuse" are protected by reuseport_lock.
231  */
232 int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
233 				       void *value, u64 map_flags)
234 {
235 	struct reuseport_array *array = reuseport_array(map);
236 	struct sock *free_osk = NULL, *osk, *nsk;
237 	struct sock_reuseport *reuse;
238 	u32 index = *(u32 *)key;
239 	uintptr_t sk_user_data;
240 	struct socket *socket;
241 	int err, fd;
242 
243 	if (map_flags > BPF_EXIST)
244 		return -EINVAL;
245 
246 	if (index >= map->max_entries)
247 		return -E2BIG;
248 
249 	if (map->value_size == sizeof(u64)) {
250 		u64 fd64 = *(u64 *)value;
251 
252 		if (fd64 > S32_MAX)
253 			return -EINVAL;
254 		fd = fd64;
255 	} else {
256 		fd = *(int *)value;
257 	}
258 
259 	socket = sockfd_lookup(fd, &err);
260 	if (!socket)
261 		return err;
262 
263 	nsk = socket->sk;
264 	if (!nsk) {
265 		err = -EINVAL;
266 		goto put_file;
267 	}
268 
269 	/* Quick checks before taking reuseport_lock */
270 	err = reuseport_array_update_check(array, nsk,
271 					   rcu_access_pointer(array->ptrs[index]),
272 					   rcu_access_pointer(nsk->sk_reuseport_cb),
273 					   map_flags);
274 	if (err)
275 		goto put_file;
276 
277 	spin_lock_bh(&reuseport_lock);
278 	/*
279 	 * Some of the checks only need reuseport_lock
280 	 * but it is done under sk_callback_lock also
281 	 * for simplicity reason.
282 	 */
283 	write_lock_bh(&nsk->sk_callback_lock);
284 
285 	osk = rcu_dereference_protected(array->ptrs[index],
286 					lockdep_is_held(&reuseport_lock));
287 	reuse = rcu_dereference_protected(nsk->sk_reuseport_cb,
288 					  lockdep_is_held(&reuseport_lock));
289 	err = reuseport_array_update_check(array, nsk, osk, reuse, map_flags);
290 	if (err)
291 		goto put_file_unlock;
292 
293 	sk_user_data = (uintptr_t)&array->ptrs[index] | SK_USER_DATA_NOCOPY |
294 		SK_USER_DATA_BPF;
295 	WRITE_ONCE(nsk->sk_user_data, (void *)sk_user_data);
296 	rcu_assign_pointer(array->ptrs[index], nsk);
297 	free_osk = osk;
298 	err = 0;
299 
300 put_file_unlock:
301 	write_unlock_bh(&nsk->sk_callback_lock);
302 
303 	if (free_osk) {
304 		write_lock_bh(&free_osk->sk_callback_lock);
305 		WRITE_ONCE(free_osk->sk_user_data, NULL);
306 		write_unlock_bh(&free_osk->sk_callback_lock);
307 	}
308 
309 	spin_unlock_bh(&reuseport_lock);
310 put_file:
311 	fput(socket->file);
312 	return err;
313 }
314 
315 /* Called from syscall */
316 static int reuseport_array_get_next_key(struct bpf_map *map, void *key,
317 					void *next_key)
318 {
319 	struct reuseport_array *array = reuseport_array(map);
320 	u32 index = key ? *(u32 *)key : U32_MAX;
321 	u32 *next = (u32 *)next_key;
322 
323 	if (index >= array->map.max_entries) {
324 		*next = 0;
325 		return 0;
326 	}
327 
328 	if (index == array->map.max_entries - 1)
329 		return -ENOENT;
330 
331 	*next = index + 1;
332 	return 0;
333 }
334 
335 static u64 reuseport_array_mem_usage(const struct bpf_map *map)
336 {
337 	struct reuseport_array *array;
338 
339 	return struct_size(array, ptrs, map->max_entries);
340 }
341 
342 BTF_ID_LIST_SINGLE(reuseport_array_map_btf_ids, struct, reuseport_array)
343 const struct bpf_map_ops reuseport_array_ops = {
344 	.map_meta_equal = bpf_map_meta_equal,
345 	.map_alloc_check = reuseport_array_alloc_check,
346 	.map_alloc = reuseport_array_alloc,
347 	.map_free = reuseport_array_free,
348 	.map_lookup_elem = reuseport_array_lookup_elem,
349 	.map_get_next_key = reuseport_array_get_next_key,
350 	.map_delete_elem = reuseport_array_delete_elem,
351 	.map_mem_usage = reuseport_array_mem_usage,
352 	.map_btf_id = &reuseport_array_map_btf_ids[0],
353 };
354