Re: [PATCH v2 net-next 6/9] af_unix: Move SOCK_PASS{CRED,PIDFD,SEC} to struct sock.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: Mon, 12 May 2025 22:44:04 -0400
> Kuniyuki Iwashima wrote:
> > From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
> > Date: Mon, 12 May 2025 15:20:54 -0400
> > > Kuniyuki Iwashima wrote:
> > > > As explained in the next patch, SO_PASSRIGHTS would have a problem
> > > > if we assigned a corresponding bit to socket->flags, so it must be
> > > > managed in struct sock.
> > > > 
> > > > Mixing socket->flags and sk->sk_flags for similar options will look
> > > > confusing, and sk->sk_flags does not have enough space on 32bit system.
> > > > 
> > > > Also, as mentioned in commit 16e572626961 ("af_unix: dont send
> > > > SCM_CREDENTIALS by default"), SOCK_PASSCRED and SOCK_PASSPID handling
> > > > is known to be slow, and managing the flags in struct socket cannot
> > > > avoid that for embryo sockets.
> > > > 
> > > > Let's move SOCK_PASS{CRED,PIDFD,SEC} to struct sock.
> > > > 
> > > > While at it, other SOCK_XXX flags in net.h are grouped as enum.
> > > > 
> > > > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > > 
> > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > index 1ab59efbafc5..9540cbe3d83e 100644
> > > > --- a/net/core/sock.c
> > > > +++ b/net/core/sock.c
> > > > @@ -1224,19 +1224,19 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
> > > >  		if (!sk_may_scm_recv(sk))
> > > >  			return -EOPNOTSUPP;
> > > >  
> > > > -		assign_bit(SOCK_PASSSEC, &sock->flags, valbool);
> > > > +		sk->sk_scm_security = valbool;
> > > 
> > > Is it safe to switch from atomic to non-atomic updates?
> > > 
> > > Reads and writes can race. Especially given that these are bit stores, so RMW.
> > 
> > Exactly, will move them down after sockopt_lock_sock().
> 
> So all reads in the datapath are with the socket locked? Okay, that
> was not immediately obvious to me. If respinning, please add a
> comment.

Sure, will add a comment.