From: Sebastien Marie <semarie@kapouay.eu.org>
Subject: Re: Unlock stat(2) & co
To: Martin Pieuchot <mpi@grenadille.net>, tech@openbsd.org
Date: Tue, 07 Jan 2025 13:47:28 +0100

Martin Pieuchot <mpi@grenadille.net> writes:

> Diff below pushes the kernel lock around namei() and vn_stat().
>
> ok?

ok semarie@
-- 
Sebastien Marie

> Index: kern/syscalls.master
> ===================================================================
> RCS file: /cvs/src/sys/kern/syscalls.master,v
> diff -u -p -r1.266 syscalls.master
> --- kern/syscalls.master	6 Jan 2025 08:57:23 -0000	1.266
> +++ kern/syscalls.master	6 Jan 2025 09:06:01 -0000
> @@ -104,11 +104,11 @@
>  35	STD		{ int sys_fchflags(int fd, u_int flags); }
>  36	STD		{ void sys_sync(void); }
>  37	OBSOL		msyscall
> -38	STD		{ int sys_stat(const char *path, struct stat *ub); }
> +38	STD NOLOCK	{ int sys_stat(const char *path, struct stat *ub); }
>  39	STD NOLOCK	{ pid_t sys_getppid(void); }
> -40	STD		{ int sys_lstat(const char *path, struct stat *ub); }
> +40	STD NOLOCK	{ int sys_lstat(const char *path, struct stat *ub); }
>  41	STD NOLOCK	{ int sys_dup(int fd); }
> -42	STD		{ int sys_fstatat(int fd, const char *path, \
> +42	STD NOLOCK	{ int sys_fstatat(int fd, const char *path, \
>  			    struct stat *buf, int flag); }
>  43	STD NOLOCK	{ gid_t sys_getegid(void); }
>  44	STD		{ int sys_profil(caddr_t samples, size_t size, \
> Index: kern/vfs_syscalls.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/vfs_syscalls.c,v
> diff -u -p -r1.370 vfs_syscalls.c
> --- kern/vfs_syscalls.c	5 Nov 2024 06:03:19 -0000	1.370
> +++ kern/vfs_syscalls.c	6 Jan 2025 09:06:02 -0000
> @@ -2066,10 +2066,14 @@ dofstatat(struct proc *p, int fd, const 
>  	NDINITAT(&nd, LOOKUP, follow | LOCKLEAF, UIO_USERSPACE, fd, path, p);
>  	nd.ni_pledge = PLEDGE_RPATH;
>  	nd.ni_unveil = UNVEIL_READ;
> -	if ((error = namei(&nd)) != 0)
> +	KERNEL_LOCK();
> +	if ((error = namei(&nd)) != 0) {
> +		KERNEL_UNLOCK();
>  		return (error);
> +	}
>  	error = vn_stat(nd.ni_vp, &sb, p);
>  	vput(nd.ni_vp);
> +	KERNEL_UNLOCK();
>  	if (error)
>  		return (error);
>  	/* Don't let non-root see generation numbers (for NFS security) */
>
>