Re: [PATCH v1 1/2] fork: add clone3

From: Christian Brauner <christian@brauner.io>
To: Yann Droneaud <ydroneaud@opteya.com>
Cc: viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org, jannh@google.com,
	fweimer@redhat.com, oleg@redhat.com, arnd@arndb.de,
	dhowells@redhat.com, Pavel Emelyanov <xemul@virtuozzo.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Adrian Reber <adrian@lisas.de>, Andrei Vagin <avagin@gmail.com>,
	linux-api@vger.kernel.org
Subject: Re: [PATCH v1 1/2] fork: add clone3
Date: Sat, 1 Jun 2019 00:08:16 +0200	[thread overview]
Message-ID: <20190531220815.owrc5kbbdemmwdhs@brauner.io> (raw)
In-Reply-To: <1058006e0df4b52b3e53c7b3202c04140899aeb5.camel@opteya.com>

On Wed, May 29, 2019 at 05:42:14PM +0200, Yann Droneaud wrote:
> Le mercredi 29 mai 2019 à 17:22 +0200, Christian Brauner a écrit :
> > This adds the clone3 system call.
> > 
> > 
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index b4cba953040a..6bc3e3d17150 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -2472,7 +2475,96 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
> >  		 unsigned long, tls)
> >  #endif
> >  {
> > -	return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls);
> > +	struct kernel_clone_args args = {
> > +		.flags = clone_flags,
> > +		.stack = newsp,
> > +		.pidfd = parent_tidptr,
> > +		.parent_tidptr = parent_tidptr,
> > +		.tls = tls,
> > +		.child_tidptr = child_tidptr,
> > +	};
> > +
> > +	/* clone(CLONE_PIDFD) uses parent_tidptr to return a pidfd */
> > +	if ((clone_flags & CLONE_PIDFD) && (clone_flags & CLONE_PARENT_SETTID))
> > +		return -EINVAL;
> > +
> > +	return _do_fork(&args);
> > +}
> > +
> > +static bool clone3_flags_valid(u64 flags)
> > +{
> > +	if (flags & CLONE_DETACHED)
> > +		return false;
> > +
> > +	if (flags & ~CLONE_MAX)
> > +		return false;
> > +
> > +	return true;
> > +}
> > +
> > +static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> > +				     struct clone_args __user *uargs,
> > +				     size_t size)
> > +{
> > +	struct clone_args args;
> > +
> > +	if (unlikely(size > PAGE_SIZE))
> > +		return -E2BIG;
> > +
> > +	if (unlikely(size < sizeof(struct clone_args)))
> > +		return -EINVAL;
> > +
> > +	if (unlikely(!access_ok(uargs, size)))
> > +		return -EFAULT;
> > +
> > +	if (size > sizeof(struct clone_args)) {
> > +		unsigned char __user *addr;
> > +		unsigned char __user *end;
> > +		unsigned char val;
> > +
> > +		addr = (void __user *)uargs + sizeof(struct clone_args);
> > +		end = (void __user *)uargs + size;
> > +
> > +		for (; addr < end; addr++) {
> > +			if (get_user(val, addr))
> > +				return -EFAULT;
> > +			if (val)
> > +				return -E2BIG;
> 
> Should be -EINVAL: having something after the structure should be
> handled just like an invalid flags, while still allowing future
> userspace program to probe for support for newer feature.

(Traveling until Monday, so sorry for delayed responses.)

This copies what:

kernel/sched/core.c:sched_copy_attr()
kernel/event/core.c:perf_copy_attr()

are already doing. Consistency might be good here but, I think.

Christian