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/slab.h>
26#include <linux/kernel.h>
27#include <linux/signal.h>
28#include <linux/list.h>
29#include <linux/anon_inodes.h>
30#include <linux/signalfd.h>
31#include <linux/syscalls.h>
32
33struct signalfd_ctx {
34    sigset_t sigmask;
35};
36
37static int signalfd_release(struct inode *inode, struct file *file)
38{
39    kfree(file->private_data);
40    return 0;
41}
42
43static unsigned int signalfd_poll(struct file *file, poll_table *wait)
44{
45    struct signalfd_ctx *ctx = file->private_data;
46    unsigned int events = 0;
47
48    poll_wait(file, &current->sighand->signalfd_wqh, wait);
49
50    spin_lock_irq(&current->sighand->siglock);
51    if (next_signal(&current->pending, &ctx->sigmask) ||
52        next_signal(&current->signal->shared_pending,
53            &ctx->sigmask))
54        events |= POLLIN;
55    spin_unlock_irq(&current->sighand->siglock);
56
57    return events;
58}
59
60/*
61 * Copied from copy_siginfo_to_user() in kernel/signal.c
62 */
63static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
64                 siginfo_t const *kinfo)
65{
66    long err;
67
68    BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
69
70    /*
71     * Unused members should be zero ...
72     */
73    err = __clear_user(uinfo, sizeof(*uinfo));
74
75    /*
76     * If you change siginfo_t structure, please be sure
77     * this code is fixed accordingly.
78     */
79    err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
80    err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
81    err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
82    switch (kinfo->si_code & __SI_MASK) {
83    case __SI_KILL:
84        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
85        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
86        break;
87    case __SI_TIMER:
88         err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
89         err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
90         err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
91         err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
92        break;
93    case __SI_POLL:
94        err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
95        err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
96        break;
97    case __SI_FAULT:
98        err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
99#ifdef __ARCH_SI_TRAPNO
100        err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
101#endif
102#ifdef BUS_MCEERR_AO
103        /*
104         * Other callers might not initialize the si_lsb field,
105         * so check explicitly for the right codes here.
106         */
107        if (kinfo->si_code == BUS_MCEERR_AR ||
108            kinfo->si_code == BUS_MCEERR_AO)
109            err |= __put_user((short) kinfo->si_addr_lsb,
110                      &uinfo->ssi_addr_lsb);
111#endif
112        break;
113    case __SI_CHLD:
114        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
115        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
116        err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
117        err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
118        err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
119        break;
120    case __SI_RT: /* This is not generated by the kernel as of now. */
121    case __SI_MESGQ: /* But this is */
122        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
123        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
124        err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
125        err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
126        break;
127    default:
128        /*
129         * This case catches also the signals queued by sigqueue().
130         */
131        err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
132        err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
133        err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
134        err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
135        break;
136    }
137
138    return err ? -EFAULT: sizeof(*uinfo);
139}
140
141static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
142                int nonblock)
143{
144    ssize_t ret;
145    DECLARE_WAITQUEUE(wait, current);
146
147    spin_lock_irq(&current->sighand->siglock);
148    ret = dequeue_signal(current, &ctx->sigmask, info);
149    switch (ret) {
150    case 0:
151        if (!nonblock)
152            break;
153        ret = -EAGAIN;
154    default:
155        spin_unlock_irq(&current->sighand->siglock);
156        return ret;
157    }
158
159    add_wait_queue(&current->sighand->signalfd_wqh, &wait);
160    for (;;) {
161        set_current_state(TASK_INTERRUPTIBLE);
162        ret = dequeue_signal(current, &ctx->sigmask, info);
163        if (ret != 0)
164            break;
165        if (signal_pending(current)) {
166            ret = -ERESTARTSYS;
167            break;
168        }
169        spin_unlock_irq(&current->sighand->siglock);
170        schedule();
171        spin_lock_irq(&current->sighand->siglock);
172    }
173    spin_unlock_irq(&current->sighand->siglock);
174
175    remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
176    __set_current_state(TASK_RUNNING);
177
178    return ret;
179}
180
181/*
182 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
183 * error code. The "count" parameter must be at least the size of a
184 * "struct signalfd_siginfo".
185 */
186static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
187                 loff_t *ppos)
188{
189    struct signalfd_ctx *ctx = file->private_data;
190    struct signalfd_siginfo __user *siginfo;
191    int nonblock = file->f_flags & O_NONBLOCK;
192    ssize_t ret, total = 0;
193    siginfo_t info;
194
195    count /= sizeof(struct signalfd_siginfo);
196    if (!count)
197        return -EINVAL;
198
199    siginfo = (struct signalfd_siginfo __user *) buf;
200    do {
201        ret = signalfd_dequeue(ctx, &info, nonblock);
202        if (unlikely(ret <= 0))
203            break;
204        ret = signalfd_copyinfo(siginfo, &info);
205        if (ret < 0)
206            break;
207        siginfo++;
208        total += ret;
209        nonblock = 1;
210    } while (--count);
211
212    return total ? total: ret;
213}
214
215static const struct file_operations signalfd_fops = {
216    .release = signalfd_release,
217    .poll = signalfd_poll,
218    .read = signalfd_read,
219    .llseek = noop_llseek,
220};
221
222SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
223        size_t, sizemask, int, flags)
224{
225    sigset_t sigmask;
226    struct signalfd_ctx *ctx;
227
228    /* Check the SFD_* constants for consistency. */
229    BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
230    BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
231
232    if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
233        return -EINVAL;
234
235    if (sizemask != sizeof(sigset_t) ||
236        copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
237        return -EINVAL;
238    sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
239    signotset(&sigmask);
240
241    if (ufd == -1) {
242        ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
243        if (!ctx)
244            return -ENOMEM;
245
246        ctx->sigmask = sigmask;
247
248        /*
249         * When we call this, the initialization must be complete, since
250         * anon_inode_getfd() will install the fd.
251         */
252        ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
253                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
254        if (ufd < 0)
255            kfree(ctx);
256    } else {
257        struct file *file = fget(ufd);
258        if (!file)
259            return -EBADF;
260        ctx = file->private_data;
261        if (file->f_op != &signalfd_fops) {
262            fput(file);
263            return -EINVAL;
264        }
265        spin_lock_irq(&current->sighand->siglock);
266        ctx->sigmask = sigmask;
267        spin_unlock_irq(&current->sighand->siglock);
268
269        wake_up(&current->sighand->signalfd_wqh);
270        fput(file);
271    }
272
273    return ufd;
274}
275
276SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
277        size_t, sizemask)
278{
279    return sys_signalfd4(ufd, user_mask, sizemask, 0);
280}
281

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