netdev - Re: [PATCH] net/unix: use consistent error code in SO

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Date: Mon, 7 Aug 2023 10:19:40 +0200
From: Alexander Mikhalitsyn <alexander@...alicyn.com>
To: David Rheinsberg <david@...dahead.eu>
Cc: netdev@...r.kernel.org, Christian Brauner <brauner@...nel.org>, 
	"David S . Miller" <davem@...emloft.net>, Stanislav Fomichev <sdf@...gle.com>, Luca Boccassi <bluca@...ian.org>, 
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] net/unix: use consistent error code in SO_PEERPIDFD

On Mon, Aug 7, 2023 at 10:12 AM David Rheinsberg <david@...dahead.eu> wrote:
>
> Change the new (unreleased) SO_PEERPIDFD sockopt to return ENODATA
> rather than ESRCH if a socket type does not support remote peer-PID
> queries.
>
> Currently, SO_PEERPIDFD returns ESRCH when the socket in question is
> not an AF_UNIX socket. This is quite unexpected, given that one would
> assume ESRCH means the peer process already exited and thus cannot be
> found. However, in that case the sockopt actually returns EINVAL (via
> pidfd_prepare()). This is rather inconsistent with other syscalls, which
> usually return ESRCH if a given PID refers to a non-existant process.
>
> This changes SO_PEERPIDFD to return ENODATA instead. This is also what
> SO_PEERGROUPS returns, and thus keeps a consistent behavior across
> sockopts.
>
> Note that this code is returned in 2 cases: First, if the socket type is
> not AF_UNIX, and secondly if the socket was not yet connected. In both
> cases ENODATA seems suitable.
>
> Signed-off-by: David Rheinsberg <david@...dahead.eu>

Hi David!

I generally agree with this. But just to be more precise, l2cap
sockets (AF_BLUETOOTH) also properly
set ->sk_peer_pid and SO_PEERPIDFD will work just fine. This thing is
not limited
only to AF_UNIX sockets.

Kind regards,
Alex

> ---
> Hi!
>
> The SO_PEERPIDFD sockopt has been queued for 6.5, so hopefully we can
> get that in before the release?
>
> Thanks
> David
>
>  net/core/sock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 6d4f28efe29a..732fc37a4771 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1778,7 +1778,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
>                 spin_unlock(&sk->sk_peer_lock);
>
>                 if (!peer_pid)
> -                       return -ESRCH;
> +                       return -ENODATA;
>
>                 pidfd = pidfd_prepare(peer_pid, 0, &pidfd_file);
>                 put_pid(peer_pid);
> --
> 2.41.0
>