xref: /openbmc/linux/kernel/bpf/reuseport_array.c (revision abe9af53)
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 
10 struct reuseport_array {
11 	struct bpf_map map;
12 	struct sock __rcu *ptrs[];
13 };
14 
15 static struct reuseport_array *reuseport_array(struct bpf_map *map)
16 {
17 	return (struct reuseport_array *)map;
18 }
19 
20 /* The caller must hold the reuseport_lock */
21 void bpf_sk_reuseport_detach(struct sock *sk)
22 {
23 	uintptr_t sk_user_data;
24 
25 	write_lock_bh(&sk->sk_callback_lock);
26 	sk_user_data = (uintptr_t)sk->sk_user_data;
27 	if (sk_user_data & SK_USER_DATA_BPF) {
28 		struct sock __rcu **socks;
29 
30 		socks = (void *)(sk_user_data & SK_USER_DATA_PTRMASK);
31 		WRITE_ONCE(sk->sk_user_data, NULL);
32 		/*
33 		 * Do not move this NULL assignment outside of
34 		 * sk->sk_callback_lock because there is
35 		 * a race with reuseport_array_free()
36 		 * which does not hold the reuseport_lock.
37 		 */
38 		RCU_INIT_POINTER(*socks, NULL);
39 	}
40 	write_unlock_bh(&sk->sk_callback_lock);
41 }
42 
43 static int reuseport_array_alloc_check(union bpf_attr *attr)
44 {
45 	if (attr->value_size != sizeof(u32) &&
46 	    attr->value_size != sizeof(u64))
47 		return -EINVAL;
48 
49 	return array_map_alloc_check(attr);
50 }
51 
52 static void *reuseport_array_lookup_elem(struct bpf_map *map, void *key)
53 {
54 	struct reuseport_array *array = reuseport_array(map);
55 	u32 index = *(u32 *)key;
56 
57 	if (unlikely(index >= array->map.max_entries))
58 		return NULL;
59 
60 	return rcu_dereference(array->ptrs[index]);
61 }
62 
63 /* Called from syscall only */
64 static int reuseport_array_delete_elem(struct bpf_map *map, void *key)
65 {
66 	struct reuseport_array *array = reuseport_array(map);
67 	u32 index = *(u32 *)key;
68 	struct sock *sk;
69 	int err;
70 
71 	if (index >= map->max_entries)
72 		return -E2BIG;
73 
74 	if (!rcu_access_pointer(array->ptrs[index]))
75 		return -ENOENT;
76 
77 	spin_lock_bh(&reuseport_lock);
78 
79 	sk = rcu_dereference_protected(array->ptrs[index],
80 				       lockdep_is_held(&reuseport_lock));
81 	if (sk) {
82 		write_lock_bh(&sk->sk_callback_lock);
83 		WRITE_ONCE(sk->sk_user_data, NULL);
84 		RCU_INIT_POINTER(array->ptrs[index], NULL);
85 		write_unlock_bh(&sk->sk_callback_lock);
86 		err = 0;
87 	} else {
88 		err = -ENOENT;
89 	}
90 
91 	spin_unlock_bh(&reuseport_lock);
92 
93 	return err;
94 }
95 
96 static void reuseport_array_free(struct bpf_map *map)
97 {
98 	struct reuseport_array *array = reuseport_array(map);
99 	struct sock *sk;
100 	u32 i;
101 
102 	/*
103 	 * ops->map_*_elem() will not be able to access this
104 	 * array now. Hence, this function only races with
105 	 * bpf_sk_reuseport_detach() which was triggerred by
106 	 * close() or disconnect().
107 	 *
108 	 * This function and bpf_sk_reuseport_detach() are
109 	 * both removing sk from "array".  Who removes it
110 	 * first does not matter.
111 	 *
112 	 * The only concern here is bpf_sk_reuseport_detach()
113 	 * may access "array" which is being freed here.
114 	 * bpf_sk_reuseport_detach() access this "array"
115 	 * through sk->sk_user_data _and_ with sk->sk_callback_lock
116 	 * held which is enough because this "array" is not freed
117 	 * until all sk->sk_user_data has stopped referencing this "array".
118 	 *
119 	 * Hence, due to the above, taking "reuseport_lock" is not
120 	 * needed here.
121 	 */
122 
123 	/*
124 	 * Since reuseport_lock is not taken, sk is accessed under
125 	 * rcu_read_lock()
126 	 */
127 	rcu_read_lock();
128 	for (i = 0; i < map->max_entries; i++) {
129 		sk = rcu_dereference(array->ptrs[i]);
130 		if (sk) {
131 			write_lock_bh(&sk->sk_callback_lock);
132 			/*
133 			 * No need for WRITE_ONCE(). At this point,
134 			 * no one is reading it without taking the
135 			 * sk->sk_callback_lock.
136 			 */
137 			sk->sk_user_data = NULL;
138 			write_unlock_bh(&sk->sk_callback_lock);
139 			RCU_INIT_POINTER(array->ptrs[i], NULL);
140 		}
141 	}
142 	rcu_read_unlock();
143 
144 	/*
145 	 * Once reaching here, all sk->sk_user_data is not
146 	 * referenceing this "array".  "array" can be freed now.
147 	 */
148 	bpf_map_area_free(array);
149 }
150 
151 static struct bpf_map *reuseport_array_alloc(union bpf_attr *attr)
152 {
153 	int err, numa_node = bpf_map_attr_numa_node(attr);
154 	struct reuseport_array *array;
155 	struct bpf_map_memory mem;
156 	u64 array_size;
157 
158 	if (!bpf_capable())
159 		return ERR_PTR(-EPERM);
160 
161 	array_size = sizeof(*array);
162 	array_size += (u64)attr->max_entries * sizeof(struct sock *);
163 
164 	err = bpf_map_charge_init(&mem, array_size);
165 	if (err)
166 		return ERR_PTR(err);
167 
168 	/* allocate all map elements and zero-initialize them */
169 	array = bpf_map_area_alloc(array_size, numa_node);
170 	if (!array) {
171 		bpf_map_charge_finish(&mem);
172 		return ERR_PTR(-ENOMEM);
173 	}
174 
175 	/* copy mandatory map attributes */
176 	bpf_map_init_from_attr(&array->map, attr);
177 	bpf_map_charge_move(&array->map.memory, &mem);
178 
179 	return &array->map;
180 }
181 
182 int bpf_fd_reuseport_array_lookup_elem(struct bpf_map *map, void *key,
183 				       void *value)
184 {
185 	struct sock *sk;
186 	int err;
187 
188 	if (map->value_size != sizeof(u64))
189 		return -ENOSPC;
190 
191 	rcu_read_lock();
192 	sk = reuseport_array_lookup_elem(map, key);
193 	if (sk) {
194 		*(u64 *)value = __sock_gen_cookie(sk);
195 		err = 0;
196 	} else {
197 		err = -ENOENT;
198 	}
199 	rcu_read_unlock();
200 
201 	return err;
202 }
203 
204 static int
205 reuseport_array_update_check(const struct reuseport_array *array,
206 			     const struct sock *nsk,
207 			     const struct sock *osk,
208 			     const struct sock_reuseport *nsk_reuse,
209 			     u32 map_flags)
210 {
211 	if (osk && map_flags == BPF_NOEXIST)
212 		return -EEXIST;
213 
214 	if (!osk && map_flags == BPF_EXIST)
215 		return -ENOENT;
216 
217 	if (nsk->sk_protocol != IPPROTO_UDP && nsk->sk_protocol != IPPROTO_TCP)
218 		return -ENOTSUPP;
219 
220 	if (nsk->sk_family != AF_INET && nsk->sk_family != AF_INET6)
221 		return -ENOTSUPP;
222 
223 	if (nsk->sk_type != SOCK_STREAM && nsk->sk_type != SOCK_DGRAM)
224 		return -ENOTSUPP;
225 
226 	/*
227 	 * sk must be hashed (i.e. listening in the TCP case or binded
228 	 * in the UDP case) and
229 	 * it must also be a SO_REUSEPORT sk (i.e. reuse cannot be NULL).
230 	 *
231 	 * Also, sk will be used in bpf helper that is protected by
232 	 * rcu_read_lock().
233 	 */
234 	if (!sock_flag(nsk, SOCK_RCU_FREE) || !sk_hashed(nsk) || !nsk_reuse)
235 		return -EINVAL;
236 
237 	/* READ_ONCE because the sk->sk_callback_lock may not be held here */
238 	if (READ_ONCE(nsk->sk_user_data))
239 		return -EBUSY;
240 
241 	return 0;
242 }
243 
244 /*
245  * Called from syscall only.
246  * The "nsk" in the fd refcnt.
247  * The "osk" and "reuse" are protected by reuseport_lock.
248  */
249 int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
250 				       void *value, u64 map_flags)
251 {
252 	struct reuseport_array *array = reuseport_array(map);
253 	struct sock *free_osk = NULL, *osk, *nsk;
254 	struct sock_reuseport *reuse;
255 	u32 index = *(u32 *)key;
256 	uintptr_t sk_user_data;
257 	struct socket *socket;
258 	int err, fd;
259 
260 	if (map_flags > BPF_EXIST)
261 		return -EINVAL;
262 
263 	if (index >= map->max_entries)
264 		return -E2BIG;
265 
266 	if (map->value_size == sizeof(u64)) {
267 		u64 fd64 = *(u64 *)value;
268 
269 		if (fd64 > S32_MAX)
270 			return -EINVAL;
271 		fd = fd64;
272 	} else {
273 		fd = *(int *)value;
274 	}
275 
276 	socket = sockfd_lookup(fd, &err);
277 	if (!socket)
278 		return err;
279 
280 	nsk = socket->sk;
281 	if (!nsk) {
282 		err = -EINVAL;
283 		goto put_file;
284 	}
285 
286 	/* Quick checks before taking reuseport_lock */
287 	err = reuseport_array_update_check(array, nsk,
288 					   rcu_access_pointer(array->ptrs[index]),
289 					   rcu_access_pointer(nsk->sk_reuseport_cb),
290 					   map_flags);
291 	if (err)
292 		goto put_file;
293 
294 	spin_lock_bh(&reuseport_lock);
295 	/*
296 	 * Some of the checks only need reuseport_lock
297 	 * but it is done under sk_callback_lock also
298 	 * for simplicity reason.
299 	 */
300 	write_lock_bh(&nsk->sk_callback_lock);
301 
302 	osk = rcu_dereference_protected(array->ptrs[index],
303 					lockdep_is_held(&reuseport_lock));
304 	reuse = rcu_dereference_protected(nsk->sk_reuseport_cb,
305 					  lockdep_is_held(&reuseport_lock));
306 	err = reuseport_array_update_check(array, nsk, osk, reuse, map_flags);
307 	if (err)
308 		goto put_file_unlock;
309 
310 	sk_user_data = (uintptr_t)&array->ptrs[index] | SK_USER_DATA_NOCOPY |
311 		SK_USER_DATA_BPF;
312 	WRITE_ONCE(nsk->sk_user_data, (void *)sk_user_data);
313 	rcu_assign_pointer(array->ptrs[index], nsk);
314 	free_osk = osk;
315 	err = 0;
316 
317 put_file_unlock:
318 	write_unlock_bh(&nsk->sk_callback_lock);
319 
320 	if (free_osk) {
321 		write_lock_bh(&free_osk->sk_callback_lock);
322 		WRITE_ONCE(free_osk->sk_user_data, NULL);
323 		write_unlock_bh(&free_osk->sk_callback_lock);
324 	}
325 
326 	spin_unlock_bh(&reuseport_lock);
327 put_file:
328 	fput(socket->file);
329 	return err;
330 }
331 
332 /* Called from syscall */
333 static int reuseport_array_get_next_key(struct bpf_map *map, void *key,
334 					void *next_key)
335 {
336 	struct reuseport_array *array = reuseport_array(map);
337 	u32 index = key ? *(u32 *)key : U32_MAX;
338 	u32 *next = (u32 *)next_key;
339 
340 	if (index >= array->map.max_entries) {
341 		*next = 0;
342 		return 0;
343 	}
344 
345 	if (index == array->map.max_entries - 1)
346 		return -ENOENT;
347 
348 	*next = index + 1;
349 	return 0;
350 }
351 
352 static int reuseport_array_map_btf_id;
353 const struct bpf_map_ops reuseport_array_ops = {
354 	.map_meta_equal = bpf_map_meta_equal,
355 	.map_alloc_check = reuseport_array_alloc_check,
356 	.map_alloc = reuseport_array_alloc,
357 	.map_free = reuseport_array_free,
358 	.map_lookup_elem = reuseport_array_lookup_elem,
359 	.map_get_next_key = reuseport_array_get_next_key,
360 	.map_delete_elem = reuseport_array_delete_elem,
361 	.map_btf_name = "reuseport_array",
362 	.map_btf_id = &reuseport_array_map_btf_id,
363 };
364