[PATCH] ir-lirc-codec: let lirc_dev handle the lirc_buffer

[David Härdeman]

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.

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.

I'm pretty certain that any driver which creates its own lirc_buffer
is quite likely to be buggy as well, but that seems to only concern
staging.

Signed-off-by: David Härdeman <da...@hardeman.nu>
---
 drivers/media/rc/ir-lirc-codec.c |   23 +++++------------------
 1 file changed, 5 insertions(+), 18 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;
 }