Subject: Re: [PATCH] af_unix: Don't set err in unix_stream_read_generic unless there was an error

From: Joseph Salisbury <[email-masked]>
Date: Thu, 11 Feb 2016 16:31:52 -0500

On 02/05/2016 05:30 PM, Rainer Weikusat wrote:
> The present unix_stream_read_generic contains various code sequences of
> the form
>
> err = -EDISASTER;
> if (<test>)
> 	goto out;
>
> This has the unfortunate side effect of possibly causing the error code
> to bleed through to the final
>
> out:
> 	return copied ? : err;
>
> and then to be wrongly returned if no data was copied because the caller
> didn't supply a data buffer, as demonstrated by the program available at
>
> http://pad.lv/1540731
>
> Change it such that err is only set if an error condition was detected.
>
> Signed-off-by: Rainer Weikusat <[email-masked]>
> ---
>
> With proper subject this time (at least I hope so).
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 49d5093..138787d 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2277,13 +2277,15 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
>  	size_t size = state->size;
>  	unsigned int last_len;
>  
> -	err = -EINVAL;
> -	if (sk->sk_state != TCP_ESTABLISHED)
> +	if (sk->sk_state != TCP_ESTABLISHED) {
> +		err = -EINVAL;
>  		goto out;
> +	}
>  
> -	err = -EOPNOTSUPP;
> -	if (flags & MSG_OOB)
> +	if (flags & MSG_OOB) {
> +		err = -EOPNOTSUPP;
>  		goto out;
> +	}
>  
>  	target = sock_rcvlowat(sk, flags & MSG_WAITALL, size);
>  	timeo = sock_rcvtimeo(sk, noblock);
> @@ -2329,9 +2331,11 @@ again:
>  				goto unlock;
>  
>  			unix_state_unlock(sk);
> -			err = -EAGAIN;
> -			if (!timeo)
> +			if (!timeo) {
> +				err = -EAGAIN;
>  				break;
> +			}
> +
>  			mutex_unlock(&u->readlock);
>  
>  			timeo = unix_stream_data_wait(sk, timeo, last,
I tested your patch, Rainer.  I can confirm that it fixes the reported
bug[0].

Thanks for the quick response!

Joe

[0] http://pad.lv/1540731