linux-kernel - Re: [PATCH] media: uvcvideo: Fix a memory leak in an error handling path of 'uvc_ioctl_ctrl

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Date:   Thu, 11 Nov 2021 13:33:03 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     laurent.pinchart@...asonboard.com, mchehab@...nel.org,
        ribalda@...omium.org, hverkuil-cisco@...all.nl,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Fix a memory leak in an error handling
 path of 'uvc_ioctl_ctrl_map()'

On Thu, Nov 11, 2021 at 09:06:11AM +0100, Christophe JAILLET wrote:
> If 'map->name' can't be allocated, 'map' must be released before returning.
> 
> Fixes: 70fa906d6fce ("media: uvcvideo: Use control names from framework")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  drivers/media/usb/uvc/uvc_v4l2.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index f4e4aff8ddf7..5aa76a9a6080 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -44,8 +44,10 @@ static int uvc_ioctl_ctrl_map(struct uvc_video_chain *chain,
>  	if (v4l2_ctrl_get_name(map->id) == NULL) {
>  		map->name = kmemdup(xmap->name, sizeof(xmap->name),
>  				    GFP_KERNEL);
> -		if (!map->name)
> +		if (!map->name) {
> +			kfree(map);
>  			return -ENOMEM;
> +		}

Your patch is fine but there is a second issue.  The error handling
should free "map->name" as well.  The problem is that this function
frees everything on the success path at all, but freeing map->name on
the success path will lead to a crash so you have to do something
weird like:

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index f4e4aff8ddf7..953a5cbf7945 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -90,6 +90,9 @@ static int uvc_ioctl_ctrl_map(struct uvc_video_chain *chain,
 	ret = uvc_ctrl_add_mapping(chain, map);
 
 	kfree(map->menu_info);
+free_name:
+	if (ret)
+		kfree(map->name);
 free_map:
 	kfree(map);