Re: [PATCH v3 2/2] binder: Validate the default binderfs device names.

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Aug 08, 2019 at 03:27:26PM -0700, Hridya Valsaraju wrote:
> Length of a binderfs device name cannot exceed BINDERFS_MAX_NAME.
> This patch adds a check in binderfs_init() to ensure the same
> for the default binder devices that will be created in every
> binderfs instance.
> 
> Co-developed-by: Christian Brauner <christian.brauner@ubuntu.com>
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
> Signed-off-by: Hridya Valsaraju <hridya@google.com>
> ---
>  drivers/android/binderfs.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
> index aee46dd1be91..55c5adb87585 100644
> --- a/drivers/android/binderfs.c
> +++ b/drivers/android/binderfs.c
> @@ -570,6 +570,18 @@ static struct file_system_type binder_fs_type = {
>  int __init init_binderfs(void)
>  {
>  	int ret;
> +	const char *name;
> +	size_t len;
> +
> +	/* Verify that the default binderfs device names are valid. */

And by "valid" you only mean "not bigger than BINDERFS_MAX_NAME, right?

> +	name = binder_devices_param;
> +	for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
> +		if (len > BINDERFS_MAX_NAME)
> +			return -E2BIG;
> +		name += len;
> +		if (*name == ',')
> +			name++;
> +	}

We already tokenize the binderfs device names in binder_init(), why not
check this there instead?  Parsing the same string over and over isn't
the nicest.

thanks,

greg k-h