Re: [PATCH][next] usb: gadget: f_fs: Use struct_size() and flex_array_size() helpers

From: Kees Cook
Date: Thu Jan 20 2022 - 18:26:58 EST


On Thu, Jan 20, 2022 at 04:29:33PM -0600, Gustavo A. R. Silva wrote:
> Make use of the struct_size() and flex_array_size() helpers instead of
> an open-coded version, in order to avoid any potential type mistakes
> or integer overflows that, in the worst scenario, could lead to heap
> overflows.
>
> Also, address the following sparse warnings:
> drivers/usb/gadget/function/f_fs.c:922:23: warning: using sizeof on a flexible structure
>
> Link: https://github.com/KSPP/linux/issues/174
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> drivers/usb/gadget/function/f_fs.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 25ad1e97a458..7461d27e9604 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -919,12 +919,12 @@ static ssize_t __ffs_epfile_read_data(struct ffs_epfile *epfile,
> data_len, ret);
>
> data_len -= ret;
> - buf = kmalloc(sizeof(*buf) + data_len, GFP_KERNEL);
> + buf = kmalloc(struct_size(buf, storage, data_len), GFP_KERNEL);
> if (!buf)
> return -ENOMEM;
> buf->length = data_len;
> buf->data = buf->storage;
> - memcpy(buf->storage, data + ret, data_len);
> + memcpy(buf->storage, data + ret, flex_array_size(buf, storage, data_len));

Looks good to me. This is a place where I think we'll be back later to
fix up the alloc/deserialize-from-memory pattern with a future helper,
but in the meantime, yes, let's get this covered by struct_size().

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

>
> /*
> * At this point read_buffer is NULL or READ_BUFFER_DROP (if
> --
> 2.27.0
>

--
Kees Cook