netdev - Re: [PATCH v2 net-next 4/9] tcp: Restrict SO

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Message-ID: <20250513031151.94700-1-kuniyu@amazon.com>
Date: Mon, 12 May 2025 20:11:18 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <willemdebruijn.kernel@...il.com>
CC: <brauner@...nel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<horms@...nel.org>, <kuba@...nel.org>, <kuni1840@...il.com>,
	<kuniyu@...zon.com>, <netdev@...r.kernel.org>, <pabeni@...hat.com>,
	<willemb@...gle.com>
Subject: Re: [PATCH v2 net-next 4/9] tcp: Restrict SO_TXREHASH to TCP socket.

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Mon, 12 May 2025 22:42:25 -0400
> Kuniyuki Iwashima wrote:
> > From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> > Date: Mon, 12 May 2025 15:18:12 -0400
> > > Kuniyuki Iwashima wrote:
> > > > sk->sk_txrehash is only used for TCP.
> > > > 
> > > > Let's restrict SO_TXREHASH to TCP to reflect this.
> > > > 
> > > > Later, we will make sk_txrehash a part of the union for other
> > > > protocol families, so we set 0 explicitly in getsockopt().
> > > > 
> > > > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > > > ---
> > > >  net/core/sock.c | 9 +++++++--
> > > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > index b64df2463300..5c84a608ddd7 100644
> > > > --- a/net/core/sock.c
> > > > +++ b/net/core/sock.c
> > > > @@ -1276,6 +1276,8 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
> > > >  		return 0;
> > > >  		}
> > > >  	case SO_TXREHASH:
> > > > +		if (!sk_is_tcp(sk))
> > > > +			return -EOPNOTSUPP;
> > > >  		if (val < -1 || val > 1)
> > > >  			return -EINVAL;
> > > >  		if ((u8)val == SOCK_TXREHASH_DEFAULT)
> > > > @@ -2102,8 +2104,11 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
> > > >  		break;
> > > >  
> > > >  	case SO_TXREHASH:
> > > > -		/* Paired with WRITE_ONCE() in sk_setsockopt() */
> > > > -		v.val = READ_ONCE(sk->sk_txrehash);
> > > > +		if (sk_is_tcp(sk))
> > > > +			/* Paired with WRITE_ONCE() in sk_setsockopt() */
> > > > +			v.val = READ_ONCE(sk->sk_txrehash);
> > > > +		else
> > > > +			v.val = 0;
> > > 
> > > Here and in the following getsockopt calls: should the call fail with
> > > EOPNOTSUPP rather than return a value that is legal where the option
> > > is supported (in TCP).
> > 
> > I was wondering which is better but didn't have preference, so will
> > return -EOPNOTSUPP in v3.
> 
> It's a reminder that this is breaking an existing API.
> 
> It is unlikely to affect any real users in this case, as SO_TXREHASH
> never was function for Unix sockets. But for this and subsequent such
> changes we have to be aware that it is in principle a user visible
> change.

I agree it's unlikely, and given we recently added 5b0af621c3f6 ("net:
restrict SO_REUSEPORT to inet sockets"), I think this type of change
is okay where it's appropriate.

And I noticed 5b0af621c3f6 didn't change getsockopt().