qemu/util/event_notifier-posix.c
Halil Pasic aa26292859 event_notifier: prevent accidental use after close
Let's set the handles to the underlying facilities to their extremal
value so no accidental misuse can happen, and to make it obvious that the
notifier is dysfunctional. E.g. if we just close an fd but do not touch
the int holding the fd eventually a read/write could succeed again when
the fd gets reused, and corrupt the file addressed by the fd.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2017-03-29 02:35:23 +03:00

126 lines
2.5 KiB
C

/*
* event notifier support
*
* Copyright Red Hat, Inc. 2010
*
* Authors:
* Michael S. Tsirkin <mst@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
#include "qemu/osdep.h"
#include "qemu-common.h"
#include "qemu/cutils.h"
#include "qemu/event_notifier.h"
#include "sysemu/char.h"
#include "qemu/main-loop.h"
#ifdef CONFIG_EVENTFD
#include <sys/eventfd.h>
#endif
#ifdef CONFIG_EVENTFD
/*
* Initialize @e with existing file descriptor @fd.
* @fd must be a genuine eventfd object, emulation with pipe won't do.
*/
void event_notifier_init_fd(EventNotifier *e, int fd)
{
e->rfd = fd;
e->wfd = fd;
}
#endif
int event_notifier_init(EventNotifier *e, int active)
{
int fds[2];
int ret;
#ifdef CONFIG_EVENTFD
ret = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
#else
ret = -1;
errno = ENOSYS;
#endif
if (ret >= 0) {
e->rfd = e->wfd = ret;
} else {
if (errno != ENOSYS) {
return -errno;
}
if (qemu_pipe(fds) < 0) {
return -errno;
}
ret = fcntl_setfl(fds[0], O_NONBLOCK);
if (ret < 0) {
ret = -errno;
goto fail;
}
ret = fcntl_setfl(fds[1], O_NONBLOCK);
if (ret < 0) {
ret = -errno;
goto fail;
}
e->rfd = fds[0];
e->wfd = fds[1];
}
if (active) {
event_notifier_set(e);
}
return 0;
fail:
close(fds[0]);
close(fds[1]);
return ret;
}
void event_notifier_cleanup(EventNotifier *e)
{
if (e->rfd != e->wfd) {
close(e->rfd);
e->rfd = -1;
}
close(e->wfd);
e->wfd = -1;
}
int event_notifier_get_fd(const EventNotifier *e)
{
return e->rfd;
}
int event_notifier_set(EventNotifier *e)
{
static const uint64_t value = 1;
ssize_t ret;
do {
ret = write(e->wfd, &value, sizeof(value));
} while (ret < 0 && errno == EINTR);
/* EAGAIN is fine, a read must be pending. */
if (ret < 0 && errno != EAGAIN) {
return -errno;
}
return 0;
}
int event_notifier_test_and_clear(EventNotifier *e)
{
int value;
ssize_t len;
char buffer[512];
/* Drain the notify pipe. For eventfd, only 8 bytes will be read. */
value = 0;
do {
len = read(e->rfd, buffer, sizeof(buffer));
value |= (len > 0);
} while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
return value;
}