2020-04-20 05:47:50

by Xiyu Yang

Subject: [PATCH] staging: comedi: Fix comedi_device refcnt leak in comedi_open

comedi_open() invokes comedi_dev_get_from_minor(), which returns a
reference of the COMEDI device to "dev" with increased refcount.

When comedi_open() returns, "dev" becomes invalid, so the refcount
should be decreased to keep refcount balanced.

The reference counting issue happens in one exception handling path of
comedi_open(). When "cfp" allocation is failed, the refcnt increased by
comedi_dev_get_from_minor() is not decreased, causing a refcnt leak.

Fix this issue by calling comedi_dev_put() on this error path when "cfp"
allocation is failed.

Fixes: 20f083c07565 ("staging: comedi: prepare support for per-file read
and write subdevices")
Signed-off-by: Xiyu Yang <[email protected]>
Signed-off-by: Xin Tan <[email protected]>
---
drivers/staging/comedi/comedi_fops.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 08d1bbbebf2d..e84b4fb493d6 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2725,8 +2725,10 @@ static int comedi_open(struct inode *inode, struct file *file)
}

cfp = kzalloc(sizeof(*cfp), GFP_KERNEL);
- if (!cfp)
+ if (!cfp) {
+ comedi_dev_put(dev);
return -ENOMEM;
+ }

cfp->dev = dev;

--
2.7.4

2020-04-20 10:24:29

by Ian Abbott

Subject: Re: [PATCH] staging: comedi: Fix comedi_device refcnt leak in comedi_open

On 20/04/2020 06:44, Xiyu Yang wrote:
> comedi_open() invokes comedi_dev_get_from_minor(), which returns a
> reference of the COMEDI device to "dev" with increased refcount.
>
> When comedi_open() returns, "dev" becomes invalid, so the refcount
> should be decreased to keep refcount balanced.
>
> The reference counting issue happens in one exception handling path of
> comedi_open(). When "cfp" allocation is failed, the refcnt increased by
> comedi_dev_get_from_minor() is not decreased, causing a refcnt leak.
>
> Fix this issue by calling comedi_dev_put() on this error path when "cfp"
> allocation is failed.
>
> Fixes: 20f083c07565 ("staging: comedi: prepare support for per-file read
> and write subdevices")
> Signed-off-by: Xiyu Yang <[email protected]>
> Signed-off-by: Xin Tan <[email protected]>
> ---
> drivers/staging/comedi/comedi_fops.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
> index 08d1bbbebf2d..e84b4fb493d6 100644
> --- a/drivers/staging/comedi/comedi_fops.c
> +++ b/drivers/staging/comedi/comedi_fops.c
> @@ -2725,8 +2725,10 @@ static int comedi_open(struct inode *inode, struct file *file)
> }
>
> cfp = kzalloc(sizeof(*cfp), GFP_KERNEL);
> - if (!cfp)
> + if (!cfp) {
> + comedi_dev_put(dev);
> return -ENOMEM;
> + }
>
> cfp->dev = dev;
>
>

Thanks for spotting that!

Signed-off-by: Ian Abbott <[email protected]>

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