Re: [PATCH] io_uring: Initialize variable before use

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

On Mon, Mar 22, 2021 at 11:41:58PM +0500, Muhammad Usama Anjum wrote:
> 1) Initialize the struct msghdr msg in the start of the function
> 2) Uninitialized variable msg.msg_flags can get used if branch happens to
> out_free before initialization.
> 
> So initialize variable in question in the start of the function for
> simplicity in logic and use.
> 
> Addresses-Coverity: ("Uninitialized variable")
> Addresses-Coverity: ("Uninitialized variable read")

This bug is a false positive.

When msg.msg_flags is uninitialized then ret is negative and min_ret is
zero.

fs/io_uring.c
  4666                  ret = -EINTR;
  4667  out_free:
  4668          if (req->flags & REQ_F_BUFFER_SELECTED)
  4669                  cflags = io_put_recv_kbuf(req);
  4670          if (ret < min_ret || ((flags & MSG_WAITALL) && (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC))))
                    ^^^^^^^^^^^^^                               ^^^^^^^^^^^^^
The first part of the condition is true so the second part is not used.

  4671                  req_set_fail_links(req);
  4672          __io_req_complete(req, issue_flags, ret, cflags);
  4673          return 0;
  4674  }

regards,
dan carpenter