linux-kernel - Re: [PATCH 2/3] misc: fastrpc: Don't remove map on creater_process and device

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Date:   Thu, 22 Sep 2022 23:46:22 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Abel Vesa <abel.vesa@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Ekansh Gupta <ekangupt@....qualcomm.com>,
        Vamsi Krishna Gattupalli <quic_vgattupa@...cinc.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ola Jeppsson <ola@...p.com>
Subject: Re: [PATCH 2/3] misc: fastrpc: Don't remove map on creater_process
 and device_release



On 02/09/2022 16:14, Abel Vesa wrote:
> Do not remove the map from the list on error path in
> fastrpc_init_create_process, instead call fastrpc_map_put, to avoid
> use-after-free. Do not remove it on fastrpc_device_release either,
> call fastrpc_map_put instead.
> 
> The fastrpc_free_map is the only proper place to remove the map.
> This is called only after the reference count is 0.
> 
> Fixes: b49f6d83e290f ("misc: fastrpc: Fix a possible double free")
> Co-developed-by: Ola Jeppsson <ola@...p.com>
> Signed-off-by: Ola Jeppsson <ola@...p.com>
> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> ---

Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>

>   drivers/misc/fastrpc.c | 18 +++++++++---------
>   1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 0c816a11eeec..50c17f5da3a8 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -316,6 +316,13 @@ static void fastrpc_free_map(struct kref *ref)
>   		dma_buf_put(map->buf);
>   	}
>   
> +	if (map->fl) {
> +		spin_lock(&map->fl->lock);
> +		list_del(&map->node);
> +		spin_unlock(&map->fl->lock);
> +		map->fl = NULL;
> +	}
> +
>   	kfree(map);
>   }
>   
> @@ -1266,12 +1273,7 @@ static int fastrpc_init_create_process(struct fastrpc_user *fl,
>   	fl->init_mem = NULL;
>   	fastrpc_buf_free(imem);
>   err_alloc:
> -	if (map) {
> -		spin_lock(&fl->lock);
> -		list_del(&map->node);
> -		spin_unlock(&fl->lock);
> -		fastrpc_map_put(map);
> -	}
> +	fastrpc_map_put(map);
>   err:
>   	kfree(args);
>   
> @@ -1347,10 +1349,8 @@ static int fastrpc_device_release(struct inode *inode, struct file *file)
>   		fastrpc_context_put(ctx);
>   	}
>   
> -	list_for_each_entry_safe(map, m, &fl->maps, node) {
> -		list_del(&map->node);
> +	list_for_each_entry_safe(map, m, &fl->maps, node)
>   		fastrpc_map_put(map);
> -	}
>   
>   	list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
>   		list_del(&buf->node);