linux-kernel - Re: [PATCH v2 1/3] fs: add ksys

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Date:   Fri, 10 May 2019 23:28:31 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     viro@...iv.linux.org.uk, linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, initramfs@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        silviu.vlasceanu@...wei.com, dmitry.kasatkin@...wei.com,
        takondra@...co.com, kamensky@...co.com, hpa@...or.com,
        arnd@...db.de, rob@...dley.net, james.w.mcmechan@...il.com
Subject: Re: [PATCH v2 1/3] fs: add ksys_lsetxattr() wrapper

On Thu, May 09, 2019 at 01:24:18PM +0200, Roberto Sassu wrote:
> Similarly to commit 03450e271a16 ("fs: add ksys_fchmod() and do_fchmodat()
> helpers and ksys_chmod() wrapper; remove in-kernel calls to syscall"), this
> patch introduces the ksys_lsetxattr() helper to avoid in-kernel calls to
> the sys_lsetxattr() syscall.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
[...]
> +int ksys_lsetxattr(const char __user *pathname,
> +		   const char __user *name, const void __user *value,
> +		   size_t size, int flags)
> +{
> +	return path_setxattr(pathname, name, value, size, flags, 0);
> +}

Instead of exposing ksys_lsetxattr(), wouldn't it be cleaner to use
kern_path() and vfs_setxattr(), or something like that? Otherwise you're
adding more code that has to cast between kernel and user pointers.