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

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Message-ID: <6822b1f41c3c0_104f1029470@willemb.c.googlers.com.notmuch>
Date: Mon, 12 May 2025 22:44:04 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>, 
 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 6/9] af_unix: Move SOCK_PASS{CRED,PIDFD,SEC}
 to struct sock.

Kuniyuki Iwashima wrote:
> From: Willem de Bruijn <willemdebruijn.kernel@...il.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@...zon.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.