`do_cmd_ioctl()` is called with the comedi device's mutex locked to
process the `COMEDI_CMD` ioctl to set up comedi's asynchronous command
handling on a comedi subdevice. `comedi_read()` and `comedi_write()`
are the `read` and `write` handlers for the comedi device, but do not
lock the mutex (for performance reasons, as some things can hold the
mutex for quite a long time).
There is a race condition if `comedi_read()` or `comedi_write()` is
running at the same time and for the same file object and comedi
subdevice as `do_cmd_ioctl()`. `do_cmd_ioctl()` sets the subdevice's
`busy` pointer to the file object way before it sets the `SRF_RUNNING` flag
in the subdevice's `runflags` member. `comedi_read() and
`comedi_write()` check the subdevice's `busy` pointer is pointing to the
current file object, then if the `SRF_RUNNING` flag is not set, will call
`do_become_nonbusy()` to shut down the asyncronous command. Bad things
can happen if the asynchronous command is being shutdown and set up at
the same time.
To prevent the race, don't set the `busy` pointer until
after the `SRF_RUNNING` flag has been set. Also, make sure the mutex is
held in `comedi_read()` and `comedi_write()` while calling
`do_become_nonbusy()` in order to avoid moving the race condition to a
point within that function.
Change some error handling `goto cleanup` statements in `do_cmd_ioctl()`
to simple `return -ERRFOO` statements as a result of changing when the
`busy` pointer is set.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
DPRINTK("subdevice busy\n");
return -EBUSY;
}
DPRINTK("subdevice busy\n");
return -EBUSY;
}
/* make sure channel/gain list isn't too long */
if (cmd.chanlist_len > s->len_chanlist) {
DPRINTK("channel/gain list too long %u > %d\n",
cmd.chanlist_len, s->len_chanlist);
/* make sure channel/gain list isn't too long */
if (cmd.chanlist_len > s->len_chanlist) {
DPRINTK("channel/gain list too long %u > %d\n",
cmd.chanlist_len, s->len_chanlist);
- ret = -EINVAL;
- goto cleanup;
}
/* make sure channel/gain list isn't too short */
if (cmd.chanlist_len < 1) {
DPRINTK("channel/gain list too short %u < 1\n",
cmd.chanlist_len);
}
/* make sure channel/gain list isn't too short */
if (cmd.chanlist_len < 1) {
DPRINTK("channel/gain list too short %u < 1\n",
cmd.chanlist_len);
- ret = -EINVAL;
- goto cleanup;
kmalloc(async->cmd.chanlist_len * sizeof(int), GFP_KERNEL);
if (!async->cmd.chanlist) {
DPRINTK("allocation failed\n");
kmalloc(async->cmd.chanlist_len * sizeof(int), GFP_KERNEL);
if (!async->cmd.chanlist) {
DPRINTK("allocation failed\n");
- ret = -ENOMEM;
- goto cleanup;
}
if (copy_from_user(async->cmd.chanlist, user_chanlist,
}
if (copy_from_user(async->cmd.chanlist, user_chanlist,
comedi_set_subdevice_runflags(s, ~0, SRF_USER | SRF_RUNNING);
comedi_set_subdevice_runflags(s, ~0, SRF_USER | SRF_RUNNING);
+ /* set s->busy _after_ setting SRF_RUNNING flag to avoid race with
+ * comedi_read() or comedi_write() */
+ s->busy = file;
ret = s->do_cmd(dev, s);
if (ret == 0)
return 0;
ret = s->do_cmd(dev, s);
if (ret == 0)
return 0;
if (!comedi_is_subdevice_running(s)) {
if (count == 0) {
if (!comedi_is_subdevice_running(s)) {
if (count == 0) {
+ mutex_lock(&dev->mutex);
if (comedi_is_subdevice_in_error(s))
retval = -EPIPE;
else
retval = 0;
do_become_nonbusy(dev, s);
if (comedi_is_subdevice_in_error(s))
retval = -EPIPE;
else
retval = 0;
do_become_nonbusy(dev, s);
+ mutex_unlock(&dev->mutex);
if (n == 0) {
if (!comedi_is_subdevice_running(s)) {
if (n == 0) {
if (!comedi_is_subdevice_running(s)) {
+ mutex_lock(&dev->mutex);
do_become_nonbusy(dev, s);
if (comedi_is_subdevice_in_error(s))
retval = -EPIPE;
else
retval = 0;
do_become_nonbusy(dev, s);
if (comedi_is_subdevice_in_error(s))
retval = -EPIPE;
else
retval = 0;
+ mutex_unlock(&dev->mutex);
break;
}
if (file->f_flags & O_NONBLOCK) {
break;
}
if (file->f_flags & O_NONBLOCK) {
buf += n;
break; /* makes device work like a pipe */
}
buf += n;
break; /* makes device work like a pipe */
}
- if (comedi_is_subdevice_idle(s) &&
- async->buf_read_count - async->buf_write_count == 0) {
- do_become_nonbusy(dev, s);
+ if (comedi_is_subdevice_idle(s)) {
+ mutex_lock(&dev->mutex);
+ if (async->buf_read_count - async->buf_write_count == 0)
+ do_become_nonbusy(dev, s);
+ mutex_unlock(&dev->mutex);
}
set_current_state(TASK_RUNNING);
remove_wait_queue(&async->wait_head, &wait);
}
set_current_state(TASK_RUNNING);
remove_wait_queue(&async->wait_head, &wait);