io_uring: don't use 'fd' for openat/openat2/statx

io_uring: don't use 'fd' for openat/openat2/statx

Based on commit 63ff822358b276137059520cf16e587e8073e80f upstream.

If an operation's flag `needs_file` is set, the function
io_req_set_file() calls io_file_get() to obtain a `struct file*`.

This fails for `O_PATH` file descriptors, because io_file_get() calls
fget(), which rejects `O_PATH` file descriptors.  To support `O_PATH`,
fdget_raw() must be used (like path_init() in `fs/namei.c` does).
This rejection causes io_req_set_file() to throw `-EBADF`.  This
breaks the operations `openat`, `openat2` and `statx`, where `O_PATH`
file descriptors are commonly used.

This could be solved by adding support for `O_PATH` file descriptors
with another `io_op_def` flag, but since those three operations don't
need the `struct file*` but operate directly on the numeric file
descriptors, the best solution here is to simply remove `needs_file`
(and the accompanying flag `fd_non_reg`).

Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <mk@cm4all.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>