Re: [PATCH] ir-lirc-codec: let lirc_dev handle the lirc_buffer (v2)

[David Härdeman]

On Mon, May 01, 2017 at 01:22:21PM +0100, Sean Young wrote:
>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. I just tested that /dev/lirc0 returned something, but not the
actual data which was returned. I'll spin a v3.

-- 
David Härdeman

Re: [PATCH] ir-lirc-codec: let lirc_dev handle the lirc_buffer (v2)

[Sean Young]

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 
> ---
>  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 = >raw->lirc;
> - drv->rbuf = rbuf;
> + drv->rbuf = NULL;
>   drv->set_use_inc = _lirc_open;
>   drv->set_use_dec = _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 = >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 

[PATCH] ir-lirc-codec: let lirc_dev handle the lirc_buffer (v2)

[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.

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 
---
 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 = >raw->lirc;
-   drv->rbuf = rbuf;
+   drv->rbuf = NULL;
drv->set_use_inc = _lirc_open;
drv->set_use_dec = _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 = >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)