1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Support for async notification of waitid
4 */
5#include <linux/kernel.h>
6#include <linux/errno.h>
7#include <linux/fs.h>
8#include <linux/file.h>
9#include <linux/compat.h>
10#include <linux/io_uring.h>
11
12#include <uapi/linux/io_uring.h>
13
14#include "io_uring.h"
15#include "cancel.h"
16#include "waitid.h"
17#include "../kernel/exit.h"
18
19static void io_waitid_cb(struct io_kiocb *req, io_tw_token_t tw);
20
21#define IO_WAITID_CANCEL_FLAG BIT(31)
22#define IO_WAITID_REF_MASK GENMASK(30, 0)
23
24struct io_waitid {
25 struct file *file;
26 int which;
27 pid_t upid;
28 int options;
29 atomic_t refs;
30 struct wait_queue_head *head;
31 struct siginfo __user *infop;
32 struct waitid_info info;
33};
34
35static void io_waitid_free(struct io_kiocb *req)
36{
37 struct io_waitid_async *iwa = req->async_data;
38
39 put_pid(pid: iwa->wo.wo_pid);
40 io_req_async_data_free(req);
41}
42
43static bool io_waitid_compat_copy_si(struct io_waitid *iw, int signo)
44{
45 struct compat_siginfo __user *infop;
46 bool ret;
47
48 infop = (struct compat_siginfo __user *) iw->infop;
49
50 if (!user_write_access_begin(infop, sizeof(*infop)))
51 return false;
52
53 unsafe_put_user(signo, &infop->si_signo, Efault);
54 unsafe_put_user(0, &infop->si_errno, Efault);
55 unsafe_put_user(iw->info.cause, &infop->si_code, Efault);
56 unsafe_put_user(iw->info.pid, &infop->si_pid, Efault);
57 unsafe_put_user(iw->info.uid, &infop->si_uid, Efault);
58 unsafe_put_user(iw->info.status, &infop->si_status, Efault);
59 ret = true;
60done:
61 user_write_access_end();
62 return ret;
63Efault:
64 ret = false;
65 goto done;
66}
67
68static bool io_waitid_copy_si(struct io_kiocb *req, int signo)
69{
70 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
71 bool ret;
72
73 if (!iw->infop)
74 return true;
75
76 if (io_is_compat(ctx: req->ctx))
77 return io_waitid_compat_copy_si(iw, signo);
78
79 if (!user_write_access_begin(iw->infop, sizeof(*iw->infop)))
80 return false;
81
82 unsafe_put_user(signo, &iw->infop->si_signo, Efault);
83 unsafe_put_user(0, &iw->infop->si_errno, Efault);
84 unsafe_put_user(iw->info.cause, &iw->infop->si_code, Efault);
85 unsafe_put_user(iw->info.pid, &iw->infop->si_pid, Efault);
86 unsafe_put_user(iw->info.uid, &iw->infop->si_uid, Efault);
87 unsafe_put_user(iw->info.status, &iw->infop->si_status, Efault);
88 ret = true;
89done:
90 user_write_access_end();
91 return ret;
92Efault:
93 ret = false;
94 goto done;
95}
96
97static int io_waitid_finish(struct io_kiocb *req, int ret)
98{
99 int signo = 0;
100
101 if (ret > 0) {
102 signo = SIGCHLD;
103 ret = 0;
104 }
105
106 if (!io_waitid_copy_si(req, signo))
107 ret = -EFAULT;
108 io_waitid_free(req);
109 return ret;
110}
111
112static void io_waitid_complete(struct io_kiocb *req, int ret)
113{
114 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
115
116 /* anyone completing better be holding a reference */
117 WARN_ON_ONCE(!(atomic_read(&iw->refs) & IO_WAITID_REF_MASK));
118
119 lockdep_assert_held(&req->ctx->uring_lock);
120
121 hlist_del_init(n: &req->hash_node);
122
123 ret = io_waitid_finish(req, ret);
124 if (ret < 0)
125 req_set_fail(req);
126 io_req_set_res(req, res: ret, cflags: 0);
127}
128
129static bool __io_waitid_cancel(struct io_kiocb *req)
130{
131 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
132 struct io_waitid_async *iwa = req->async_data;
133
134 /*
135 * Mark us canceled regardless of ownership. This will prevent a
136 * potential retry from a spurious wakeup.
137 */
138 atomic_or(IO_WAITID_CANCEL_FLAG, v: &iw->refs);
139
140 /* claim ownership */
141 if (atomic_fetch_inc(v: &iw->refs) & IO_WAITID_REF_MASK)
142 return false;
143
144 spin_lock_irq(lock: &iw->head->lock);
145 list_del_init(entry: &iwa->wo.child_wait.entry);
146 spin_unlock_irq(lock: &iw->head->lock);
147 io_waitid_complete(req, ret: -ECANCELED);
148 io_req_queue_tw_complete(req, res: -ECANCELED);
149 return true;
150}
151
152int io_waitid_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
153 unsigned int issue_flags)
154{
155 return io_cancel_remove(ctx, cd, issue_flags, list: &ctx->waitid_list, cancel: __io_waitid_cancel);
156}
157
158bool io_waitid_remove_all(struct io_ring_ctx *ctx, struct io_uring_task *tctx,
159 bool cancel_all)
160{
161 return io_cancel_remove_all(ctx, tctx, list: &ctx->waitid_list, cancel_all, cancel: __io_waitid_cancel);
162}
163
164static inline bool io_waitid_drop_issue_ref(struct io_kiocb *req)
165{
166 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
167 struct io_waitid_async *iwa = req->async_data;
168
169 if (!atomic_sub_return(i: 1, v: &iw->refs))
170 return false;
171
172 /*
173 * Wakeup triggered, racing with us. It was prevented from
174 * completing because of that, queue up the tw to do that.
175 */
176 req->io_task_work.func = io_waitid_cb;
177 io_req_task_work_add(req);
178 remove_wait_queue(wq_head: iw->head, wq_entry: &iwa->wo.child_wait);
179 return true;
180}
181
182static void io_waitid_cb(struct io_kiocb *req, io_tw_token_t tw)
183{
184 struct io_waitid_async *iwa = req->async_data;
185 struct io_ring_ctx *ctx = req->ctx;
186 int ret;
187
188 io_tw_lock(ctx, tw);
189
190 ret = __do_wait(wo: &iwa->wo);
191
192 /*
193 * If we get -ERESTARTSYS here, we need to re-arm and check again
194 * to ensure we get another callback. If the retry works, then we can
195 * just remove ourselves from the waitqueue again and finish the
196 * request.
197 */
198 if (unlikely(ret == -ERESTARTSYS)) {
199 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
200
201 /* Don't retry if cancel found it meanwhile */
202 ret = -ECANCELED;
203 if (!(atomic_read(v: &iw->refs) & IO_WAITID_CANCEL_FLAG)) {
204 iw->head = &current->signal->wait_chldexit;
205 add_wait_queue(wq_head: iw->head, wq_entry: &iwa->wo.child_wait);
206 ret = __do_wait(wo: &iwa->wo);
207 if (ret == -ERESTARTSYS) {
208 /* retry armed, drop our ref */
209 io_waitid_drop_issue_ref(req);
210 return;
211 }
212
213 remove_wait_queue(wq_head: iw->head, wq_entry: &iwa->wo.child_wait);
214 }
215 }
216
217 io_waitid_complete(req, ret);
218 io_req_task_complete(req, tw);
219}
220
221static int io_waitid_wait(struct wait_queue_entry *wait, unsigned mode,
222 int sync, void *key)
223{
224 struct wait_opts *wo = container_of(wait, struct wait_opts, child_wait);
225 struct io_waitid_async *iwa = container_of(wo, struct io_waitid_async, wo);
226 struct io_kiocb *req = iwa->req;
227 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
228 struct task_struct *p = key;
229
230 if (!pid_child_should_wake(wo, p))
231 return 0;
232
233 list_del_init(entry: &wait->entry);
234
235 /* cancel is in progress */
236 if (atomic_fetch_inc(v: &iw->refs) & IO_WAITID_REF_MASK)
237 return 1;
238
239 req->io_task_work.func = io_waitid_cb;
240 io_req_task_work_add(req);
241 return 1;
242}
243
244int io_waitid_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
245{
246 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
247 struct io_waitid_async *iwa;
248
249 if (sqe->addr || sqe->buf_index || sqe->addr3 || sqe->waitid_flags)
250 return -EINVAL;
251
252 iwa = io_uring_alloc_async_data(NULL, req);
253 if (!unlikely(iwa))
254 return -ENOMEM;
255 iwa->req = req;
256
257 iw->which = READ_ONCE(sqe->len);
258 iw->upid = READ_ONCE(sqe->fd);
259 iw->options = READ_ONCE(sqe->file_index);
260 iw->infop = u64_to_user_ptr(READ_ONCE(sqe->addr2));
261 return 0;
262}
263
264int io_waitid(struct io_kiocb *req, unsigned int issue_flags)
265{
266 struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
267 struct io_waitid_async *iwa = req->async_data;
268 struct io_ring_ctx *ctx = req->ctx;
269 int ret;
270
271 ret = kernel_waitid_prepare(wo: &iwa->wo, which: iw->which, upid: iw->upid, infop: &iw->info,
272 options: iw->options, NULL);
273 if (ret)
274 goto done;
275
276 /*
277 * Mark the request as busy upfront, in case we're racing with the
278 * wakeup. If we are, then we'll notice when we drop this initial
279 * reference again after arming.
280 */
281 atomic_set(v: &iw->refs, i: 1);
282
283 /*
284 * Cancel must hold the ctx lock, so there's no risk of cancelation
285 * finding us until a) we remain on the list, and b) the lock is
286 * dropped. We only need to worry about racing with the wakeup
287 * callback.
288 */
289 io_ring_submit_lock(ctx, issue_flags);
290 hlist_add_head(n: &req->hash_node, h: &ctx->waitid_list);
291
292 init_waitqueue_func_entry(wq_entry: &iwa->wo.child_wait, func: io_waitid_wait);
293 iwa->wo.child_wait.private = req->tctx->task;
294 iw->head = &current->signal->wait_chldexit;
295 add_wait_queue(wq_head: iw->head, wq_entry: &iwa->wo.child_wait);
296
297 ret = __do_wait(wo: &iwa->wo);
298 if (ret == -ERESTARTSYS) {
299 /*
300 * Nobody else grabbed a reference, it'll complete when we get
301 * a waitqueue callback, or if someone cancels it.
302 */
303 if (!io_waitid_drop_issue_ref(req)) {
304 io_ring_submit_unlock(ctx, issue_flags);
305 return IOU_ISSUE_SKIP_COMPLETE;
306 }
307
308 /*
309 * Wakeup triggered, racing with us. It was prevented from
310 * completing because of that, queue up the tw to do that.
311 */
312 io_ring_submit_unlock(ctx, issue_flags);
313 return IOU_ISSUE_SKIP_COMPLETE;
314 }
315
316 hlist_del_init(n: &req->hash_node);
317 remove_wait_queue(wq_head: iw->head, wq_entry: &iwa->wo.child_wait);
318 ret = io_waitid_finish(req, ret);
319
320 io_ring_submit_unlock(ctx, issue_flags);
321done:
322 if (ret < 0)
323 req_set_fail(req);
324 io_req_set_res(req, res: ret, cflags: 0);
325 return IOU_COMPLETE;
326}
327