netdev - Re: [PATCH v4] net/af_unix: don't create a path for a bound socket

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Date:   Thu, 3 Dec 2020 08:30:35 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Denis Kirjanov <kda@...ux-powerpc.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH v4] net/af_unix: don't create a path for a bound socket

On Thu,  3 Dec 2020 11:18:44 +0300 Denis Kirjanov wrote:
> in the case of a socket which is already bound to an adress
> there is no sense to create a path in the next attempts

> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 41c3303c3357..489d49a1739c 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1029,6 +1029,16 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
>  		goto out;
>  	}
>  
> +	/* check if we're already bound to a path */
> +	err = mutex_lock_interruptible(&u->bindlock);
> +	if (err)
> +		goto out;
> +	if (u->addr)
> +		err = -EINVAL;
> +	mutex_unlock(&u->bindlock);

This, like v1, is not atomic with the creation, two threads can pass
this check and then try to assign to u->addr.

Naive question - can't we add the removal of the unnecessary node in
the error path, in the kernel?

> +	if (err)
> +		goto out;
> +
>  	err = unix_mkname(sunaddr, addr_len, &hash);
>  	if (err < 0)
>  		goto out;
> @@ -1049,10 +1059,6 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
>  	if (err)
>  		goto out_put;
>  
> -	err = -EINVAL;
> -	if (u->addr)
> -		goto out_up;
> -
>  	err = -ENOMEM;
>  	addr = kmalloc(sizeof(*addr)+addr_len, GFP_KERNEL);
>  	if (!addr)