Hi Al,
Lars-Peter Clausen <lars@xxxxxxxxxx> writes:
> In the current implementation functionfs generates a EFAULT for async read
> operations if the read buffer size is larger than the URB data size. Since
> a application does not necessarily know how much data the host side is
> going to send it typically supplies a buffer larger than the actual data,
> which will then result in a EFAULT error.
>
> This behaviour was introduced while refactoring the code to use iov_iter
> interface in commit c993c39b8639 ("gadget/function/f_fs.c: use put iov_iter
> into io_data"). The original code took the minimum over the URB size and
> the user buffer size and then attempted to copy that many bytes using
> copy_to_user(). If copy_to_user() could not copy all data a EFAULT error
> was generated. Restore the original behaviour by only generating a EFAULT
> error when the number of bytes copied is not the size of the URB and the
> target buffer has not been fully filled.
>
> Commit 342f39a6c8d3 ("usb: gadget: f_fs: fix check in read operation")
> already fixed the same problem for the synchronous read path.
>
> Fixes: c993c39b8639 ("gadget/function/f_fs.c: use put iov_iter into io_data")
> Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> ---
> Changes since v1:
> * copy_to_iter() can fail, make sure that is handled. Test this case by
> mapping part of the target buffer read-only.
>
> Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> ---
> drivers/usb/gadget/function/f_fs.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 8cfce10..3b27aa0 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -650,7 +650,7 @@ static void ffs_user_copy_worker(struct work_struct *work)
> if (io_data->read && ret > 0) {
> use_mm(io_data->mm);
> ret = copy_to_iter(io_data->buf, ret, &io_data->data);
> - if (iov_iter_count(&io_data->data))
> + if (ret != io_data->req->actual && iov_iter_count(&io_data->data))
> ret = -EFAULT;
> unuse_mm(io_data->mm);
> }
does this look good for you now ?
--
balbi
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