[lvc-project] [PATCH] [RFC] net: smc: fix fasync leak in smc_release()

[Dmitry Antipov]

On 2/23/24 06:36, Wen Gu wrote:

> One solution to this issue I can think of is to check whether
> filp->private_data has been changed when the sock_fasync holds the sock lock,
> but it inevitably changes the general code..
> 
> diff --git a/net/socket.c b/net/socket.c
> index ed3df2f749bf..a28435195854 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1443,6 +1443,11 @@ static int sock_fasync(int fd, struct file *filp, int on)
>                  return -EINVAL;
> 
>          lock_sock(sk);
> +       /* filp->private_data has changed */
> +       if (on && unlikely(sock != filp->private_data)) {
> +               release_sock(sk);
> +               return -EAGAIN;
> +       }
>          fasync_helper(fd, filp, on, &wq->fasync_list);
> 
>          if (!wq->fasync_list)
> 
> Let's see if anyone else has a better idea.

IIUC this is not a solution just because it decreases the probability of the race
but doesn't eliminate it completely - an underlying socket switch (e.g. changing
'filp->private_data') may happen when 'fasync_helper()' is in progress.

Dmitry