Root/fs/signalfd.c

1/*
2 * fs/signalfd.c
3 *
4 * Copyright (C) 2003 Linus Torvalds
5 *
6 * Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
7 * Changed ->read() to return a siginfo strcture instead of signal number.
8 * Fixed locking in ->poll().
9 * Added sighand-detach notification.
10 * Added fd re-use in sys_signalfd() syscall.
11 * Now using anonymous inode source.
12 * Thanks to Oleg Nesterov for useful code review and suggestions.
13 * More comments and suggestions from Arnd Bergmann.
14 * Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
15 * Retrieve multiple signals with one read() call
16 * Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
17 * Attach to the sighand only during read() and poll().
18 */
19
20#include <linux/file.h>
21#include <linux/poll.h>
22#include <linux/init.h>
23#include <linux/fs.h>
24#include <linux/sched.h>
25#include <linux/kernel.h>
26#include <linux/signal.h>
27#include <linux/list.h>
28#include <linux/anon_inodes.h>
29#include <linux/signalfd.h>
30#include <linux/syscalls.h>
31
32struct signalfd_ctx {
33    sigset_t sigmask;
34};
35
36static int signalfd_release(struct inode *inode, struct file *file)
37{
38    kfree(file->private_data);
39    return 0;
40}
41
42static unsigned int signalfd_poll(struct file *file, poll_table *wait)
43{
44    struct signalfd_ctx *ctx = file->private_data;
45    unsigned int events = 0;
46
47    poll_wait(file, &current->sighand->signalfd_wqh, wait);
48
49    spin_lock_irq(&current->sighand->siglock);
50    if (next_signal(&current->pending, &ctx->sigmask) ||
51        next_signal(&current->signal->shared_pending,
52            &ctx->sigmask))
53        events |= POLLIN;
54    spin_unlock_irq(&current->sighand->siglock);
55
56    return events;
57}
58
59/*
60 * Copied from copy_siginfo_to_user() in kernel/signal.c
61 */
62static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
63                 siginfo_t const *kinfo)
64{
65    long err;
66
67    BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
68
69    /*
70     * Unused members should be zero ...
71     */
72    err = __clear_user(uinfo, sizeof(*uinfo));
73
74    /*
75     * If you change siginfo_t structure, please be sure
76     * this code is fixed accordingly.
77     */
78    err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
79    err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
80    err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
81    switch (kinfo->si_code & __SI_MASK) {
82    case __SI_KILL:
83        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
84        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
85        break;
86    case __SI_TIMER:
87         err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
88         err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
89         err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
90        break;
91    case __SI_POLL:
92        err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
93        err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
94        break;
95    case __SI_FAULT:
96        err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
97#ifdef __ARCH_SI_TRAPNO
98        err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
99#endif
100        break;
101    case __SI_CHLD:
102        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
103        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
104        err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
105        err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
106        err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
107        break;
108    case __SI_RT: /* This is not generated by the kernel as of now. */
109    case __SI_MESGQ: /* But this is */
110        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
111        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
112        err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
113        break;
114    default:
115        /*
116         * This case catches also the signals queued by sigqueue().
117         */
118        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
119        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
120        err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
121        err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
122        break;
123    }
124
125    return err ? -EFAULT: sizeof(*uinfo);
126}
127
128static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
129                int nonblock)
130{
131    ssize_t ret;
132    DECLARE_WAITQUEUE(wait, current);
133
134    spin_lock_irq(&current->sighand->siglock);
135    ret = dequeue_signal(current, &ctx->sigmask, info);
136    switch (ret) {
137    case 0:
138        if (!nonblock)
139            break;
140        ret = -EAGAIN;
141    default:
142        spin_unlock_irq(&current->sighand->siglock);
143        return ret;
144    }
145
146    add_wait_queue(&current->sighand->signalfd_wqh, &wait);
147    for (;;) {
148        set_current_state(TASK_INTERRUPTIBLE);
149        ret = dequeue_signal(current, &ctx->sigmask, info);
150        if (ret != 0)
151            break;
152        if (signal_pending(current)) {
153            ret = -ERESTARTSYS;
154            break;
155        }
156        spin_unlock_irq(&current->sighand->siglock);
157        schedule();
158        spin_lock_irq(&current->sighand->siglock);
159    }
160    spin_unlock_irq(&current->sighand->siglock);
161
162    remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
163    __set_current_state(TASK_RUNNING);
164
165    return ret;
166}
167
168/*
169 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
170 * error code. The "count" parameter must be at least the size of a
171 * "struct signalfd_siginfo".
172 */
173static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
174                 loff_t *ppos)
175{
176    struct signalfd_ctx *ctx = file->private_data;
177    struct signalfd_siginfo __user *siginfo;
178    int nonblock = file->f_flags & O_NONBLOCK;
179    ssize_t ret, total = 0;
180    siginfo_t info;
181
182    count /= sizeof(struct signalfd_siginfo);
183    if (!count)
184        return -EINVAL;
185
186    siginfo = (struct signalfd_siginfo __user *) buf;
187    do {
188        ret = signalfd_dequeue(ctx, &info, nonblock);
189        if (unlikely(ret <= 0))
190            break;
191        ret = signalfd_copyinfo(siginfo, &info);
192        if (ret < 0)
193            break;
194        siginfo++;
195        total += ret;
196        nonblock = 1;
197    } while (--count);
198
199    return total ? total: ret;
200}
201
202static const struct file_operations signalfd_fops = {
203    .release = signalfd_release,
204    .poll = signalfd_poll,
205    .read = signalfd_read,
206};
207
208SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
209        size_t, sizemask, int, flags)
210{
211    sigset_t sigmask;
212    struct signalfd_ctx *ctx;
213
214    /* Check the SFD_* constants for consistency. */
215    BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
216    BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
217
218    if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
219        return -EINVAL;
220
221    if (sizemask != sizeof(sigset_t) ||
222        copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
223        return -EINVAL;
224    sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
225    signotset(&sigmask);
226
227    if (ufd == -1) {
228        ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
229        if (!ctx)
230            return -ENOMEM;
231
232        ctx->sigmask = sigmask;
233
234        /*
235         * When we call this, the initialization must be complete, since
236         * anon_inode_getfd() will install the fd.
237         */
238        ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
239                       flags & (O_CLOEXEC | O_NONBLOCK));
240        if (ufd < 0)
241            kfree(ctx);
242    } else {
243        struct file *file = fget(ufd);
244        if (!file)
245            return -EBADF;
246        ctx = file->private_data;
247        if (file->f_op != &signalfd_fops) {
248            fput(file);
249            return -EINVAL;
250        }
251        spin_lock_irq(&current->sighand->siglock);
252        ctx->sigmask = sigmask;
253        spin_unlock_irq(&current->sighand->siglock);
254
255        wake_up(&current->sighand->signalfd_wqh);
256        fput(file);
257    }
258
259    return ufd;
260}
261
262SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
263        size_t, sizemask)
264{
265    return sys_signalfd4(ufd, user_mask, sizemask, 0);
266}
267

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