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 attempt to copy that many bytes using
copy_to_user(). If copy_to_user() returned less copied bytes the code would
generate a EFAULT error. This has exactly the same behaviour as using
copy_to_iter() except that copy_to_iter() can't fail since the check
whether access to the user supplied buffer is OK is already done earlier
and copy_to_iter() wont be called in that case. Restore the original
behaviour by simply dropping the code that generates the EFAULT error.
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>
---
drivers/usb/gadget/function/f_fs.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 8cfce10..e219379 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -650,8 +650,6 @@ 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))
- ret = -EFAULT;
unuse_mm(io_data->mm);
}
--
2.1.4
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