On Sat, Apr 29, 2017 at 11:22:28PM +0200, David Härdeman wrote:
> ir_lirc_register() currently creates its own lirc_buffer before
> passing the lirc_driver to lirc_register_driver().
>
> When a module is later unloaded, ir_lirc_unregister() gets called
> which performs a call to lirc_unregister_driver() and then free():s
> the lirc_buffer.
>
> The problem is that:
>
> a) there can still be a userspace app holding an open lirc fd
> when lirc_unregister_driver() returns; and
>
> b) the lirc_buffer contains "wait_queue_head_t wait_poll" which
> is potentially used as long as any userspace app is still around.
>
> The result is an oops which can be triggered quite easily by a
> userspace app monitoring its lirc fd using epoll() and not closing
> the fd promptly on device removal.
You're right, the rbuf is freed too early. Good catch! I missed this one.
However, when I test your patch it does not work.
[sean@bigcore bin]$ ./ir-ctl -d /dev/lirc1 -r
/dev/lirc1: read returned 2 bytes
The lirc_buffer is no longer has a chunk size of 4.
Thanks,
Sean
>
> The minimalistic fix is to let lirc_dev create the lirc_buffer since
> lirc_dev will then also free the buffer once it believes it is safe to
> do so.
>
> Version 2: make sure that the allocated buffer is communicated back to
> ir-lirc-codec so that ir_lirc_decode() can use it.
>
> CC: sta...@vger.kernel.org
> Signed-off-by: David Härdeman <da...@hardeman.nu>
> ---
> drivers/media/rc/ir-lirc-codec.c | 23 +++++------------------
> drivers/media/rc/lirc_dev.c | 13 ++++++++++++-
> 2 files changed, 17 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/media/rc/ir-lirc-codec.c
> b/drivers/media/rc/ir-lirc-codec.c
> index de85f1d7ce43..7b961357d333 100644
> --- a/drivers/media/rc/ir-lirc-codec.c
> +++ b/drivers/media/rc/ir-lirc-codec.c
> @@ -354,7 +354,6 @@ static const struct file_operations lirc_fops = {
> static int ir_lirc_register(struct rc_dev *dev)
> {
> struct lirc_driver *drv;
> - struct lirc_buffer *rbuf;
> int rc = -ENOMEM;
> unsigned long features = 0;
>
> @@ -362,19 +361,12 @@ static int ir_lirc_register(struct rc_dev *dev)
> if (!drv)
> return rc;
>
> - rbuf = kzalloc(sizeof(struct lirc_buffer), GFP_KERNEL);
> - if (!rbuf)
> - goto rbuf_alloc_failed;
> -
> - rc = lirc_buffer_init(rbuf, sizeof(int), LIRCBUF_SIZE);
> - if (rc)
> - goto rbuf_init_failed;
> -
> if (dev->driver_type != RC_DRIVER_IR_RAW_TX) {
> features |= LIRC_CAN_REC_MODE2;
> if (dev->rx_resolution)
> features |= LIRC_CAN_GET_REC_RESOLUTION;
> }
> +
> if (dev->tx_ir) {
> features |= LIRC_CAN_SEND_PULSE;
> if (dev->s_tx_mask)
> @@ -403,7 +395,7 @@ static int ir_lirc_register(struct rc_dev *dev)
> drv->minor = -1;
> drv->features = features;
> drv->data = &dev->raw->lirc;
> - drv->rbuf = rbuf;
> + drv->rbuf = NULL;
> drv->set_use_inc = &ir_lirc_open;
> drv->set_use_dec = &ir_lirc_close;
> drv->code_length = sizeof(struct ir_raw_event) * 8;
> @@ -415,19 +407,15 @@ static int ir_lirc_register(struct rc_dev *dev)
> drv->minor = lirc_register_driver(drv);
> if (drv->minor < 0) {
> rc = -ENODEV;
> - goto lirc_register_failed;
> + goto out;
> }
>
> dev->raw->lirc.drv = drv;
> dev->raw->lirc.dev = dev;
> return 0;
>
> -lirc_register_failed:
> -rbuf_init_failed:
> - kfree(rbuf);
> -rbuf_alloc_failed:
> +out:
> kfree(drv);
> -
> return rc;
> }
>
> @@ -436,9 +424,8 @@ static int ir_lirc_unregister(struct rc_dev *dev)
> struct lirc_codec *lirc = &dev->raw->lirc;
>
> lirc_unregister_driver(lirc->drv->minor);
> - lirc_buffer_free(lirc->drv->rbuf);
> - kfree(lirc->drv->rbuf);
> kfree(lirc->drv);
> + lirc->drv = NULL;
>
> return 0;
> }
> diff --git a/drivers/media/rc/lirc_dev.c b/drivers/media/rc/lirc_dev.c
> index 8d60c9f00df9..42704552b005 100644
> --- a/drivers/media/rc/lirc_dev.c
> +++ b/drivers/media/rc/lirc_dev.c
> @@ -52,6 +52,7 @@ struct irctl {
>
> struct mutex irctl_lock;
> struct lirc_buffer *buf;
> + bool buf_internal;
> unsigned int chunk_size;
>
> struct device dev;
> @@ -83,7 +84,7 @@ static void lirc_release(struct device *ld)
>
> put_device(ir->dev.parent);
>
> - if (ir->buf != ir->d.rbuf) {
> + if (ir->buf_internal) {
> lirc_buffer_free(ir->buf);
> kfree(ir->buf);
> }
> @@ -198,6 +199,7 @@ static int lirc_allocate_buffer(struct irctl *ir)
>
> if (d->rbuf) {
> ir->buf = d->rbuf;
> + ir->buf_internal = false;
> } else {
> ir->buf = kmalloc(sizeof(struct lirc_buffer), GFP_KERNEL);
> if (!ir->buf) {
> @@ -208,8 +210,11 @@ static int lirc_allocate_buffer(struct irctl *ir)
> err = lirc_buffer_init(ir->buf, chunk_size, buffer_size);
> if (err) {
> kfree(ir->buf);
> + ir->buf = NULL;
> goto out;
> }
> +
> + ir->buf_internal = true;
> }
> ir->chunk_size = ir->buf->chunk_size;
>
> @@ -362,6 +367,12 @@ int lirc_register_driver(struct lirc_driver *d)
> err = lirc_allocate_buffer(irctls[minor]);
> if (err)
> lirc_unregister_driver(minor);
> + else
> + /*
> + * This is kind of a hack but ir-lirc-codec needs
> + * access to the buffer that lirc_dev allocated.
> + */
> + d->rbuf = irctls[minor]->buf;
> }
>
> return err ? err : minor;
