Re: [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process

From: Michal Hocko <mhocko@kernel.org>
To: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Hari Bathini <hbathini@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] fork.c: Move check of clone NEWIPC and SYSVSEM to copy_process
Date: Thu, 30 Nov 2017 11:04:06 +0100	[thread overview]
Message-ID: <20171130100406.qnn2zofbfaviorgs@dhcp22.suse.cz> (raw)
In-Reply-To: <20171126160717.14727-1-marcos.souza.org@gmail.com>

CC Eric

On Sun 26-11-17 14:06:52, Marcos Paulo de Souza wrote:
> Currently this check for CLONE_NEWIPC with CLONE_SYSVSEM is done inside
> copy_namespaces, resulting in a handful of error paths being executed if
> these flags were used together. So, move this check to the beginning of
> copy_process, exiting earlier if the condition is true.
> 
> This move is safe because copy_namespaces is called just from
> copy_process function.

I am not familiar with the code all that much but the justification is
not clear to me. Thesea re namespace related flags so why should we pull
them out of copy_namespaces. I do not see any simplifications in the
error code paths or something like that.

> Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> ---
>  kernel/fork.c    | 11 +++++++++++
>  kernel/nsproxy.c | 11 -----------
>  2 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 2113e252cb9d..691f9ba135fc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1600,6 +1600,17 @@ static __latent_entropy struct task_struct *copy_process(
>  		return ERR_PTR(-EINVAL);
>  
>  	/*
> +	 * CLONE_NEWIPC must detach from the undolist: after switching
> +	 * to a new ipc namespace, the semaphore arrays from the old
> +	 * namespace are unreachable.  In clone parlance, CLONE_SYSVSEM
> +	 * means share undolist with parent, so we must forbid using
> +	 * it along with CLONE_NEWIPC.
> +	 */
> +	if ((clone_flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> +		(CLONE_NEWIPC | CLONE_SYSVSEM))
> +		return ERR_PTR(-EINVAL);
> +
> +	/*
>  	 * Thread groups must share signals as well, and detached threads
>  	 * can only be started up within the thread group.
>  	 */
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index f6c5d330059a..30882727dff5 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -151,17 +151,6 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
>  	if (!ns_capable(user_ns, CAP_SYS_ADMIN))
>  		return -EPERM;
>  
> -	/*
> -	 * CLONE_NEWIPC must detach from the undolist: after switching
> -	 * to a new ipc namespace, the semaphore arrays from the old
> -	 * namespace are unreachable.  In clone parlance, CLONE_SYSVSEM
> -	 * means share undolist with parent, so we must forbid using
> -	 * it along with CLONE_NEWIPC.
> -	 */
> -	if ((flags & (CLONE_NEWIPC | CLONE_SYSVSEM)) ==
> -		(CLONE_NEWIPC | CLONE_SYSVSEM)) 
> -		return -EINVAL;
> -
>  	new_ns = create_new_namespaces(flags, tsk, user_ns, tsk->fs);
>  	if (IS_ERR(new_ns))
>  		return  PTR_ERR(new_ns);
> -- 
> 2.13.6
> 

-- 
Michal Hocko
SUSE Labs