From: Vitaliy Makkoveev <otto@bsdbox.dev>
Subject: Re: fstat socket buffer mutex
To: Alexander Bluhm <bluhm@openbsd.org>
Cc: tech@openbsd.org
Date: Sat, 9 Nov 2024 17:50:33 +0300

> On 9 Nov 2024, at 17:38, Alexander Bluhm <bluhm@openbsd.org> wrote:
> 
> Hi,
> 
> I wonder if we should also lock so_snd in soo_stat().  Take so_rcv
> and so_snd mutex together to provide consistent view to userland.
> 
> ok?
> 

We set SS_CANTRCVMORE and SS_CANTSENDMORE independently from each
other, no consistency between them.

I locked so_rcv to keep consistency between sb_cc and sb_state,
but no locks required for so_snd because we only check sb_state.

> bluhm
> 
> Index: kern/sys_socket.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/kern/sys_socket.c,v
> diff -u -p -r1.65 sys_socket.c
> --- kern/sys_socket.c	30 Apr 2024 17:59:15 -0000	1.65
> +++ kern/sys_socket.c	9 Nov 2024 14:33:20 -0000
> @@ -149,12 +149,14 @@ soo_stat(struct file *fp, struct stat *u
> 	ub->st_mode = S_IFSOCK;
> 	solock_shared(so);
> 	mtx_enter(&so->so_rcv.sb_mtx);
> +	mtx_enter(&so->so_snd.sb_mtx);
> 	if ((so->so_rcv.sb_state & SS_CANTRCVMORE) == 0 ||
> 	    so->so_rcv.sb_cc != 0)
> 		ub->st_mode |= S_IRUSR | S_IRGRP | S_IROTH;
> -	mtx_leave(&so->so_rcv.sb_mtx);
> 	if ((so->so_snd.sb_state & SS_CANTSENDMORE) == 0)
> 		ub->st_mode |= S_IWUSR | S_IWGRP | S_IWOTH;
> +	mtx_leave(&so->so_snd.sb_mtx);
> +	mtx_leave(&so->so_rcv.sb_mtx);
> 	ub->st_uid = so->so_euid;
> 	ub->st_gid = so->so_egid;
> 	(void)pru_sense(so, ub);
>