linux-kernel - Re: [PATCH] exec: Copy oldsighand->action under spin-lock

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Message-ID: <202106071617.5713E0A01@keescook>
Date:   Mon, 7 Jun 2021 16:17:41 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Bernd Edlinger <bernd.edlinger@...mail.de>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] exec: Copy oldsighand->action under spin-lock

On Mon, Jun 07, 2021 at 03:54:27PM +0200, Bernd Edlinger wrote:
> unshare_sighand should only access oldsighand->action
> while holding oldsighand->siglock, to make sure that
> newsighand->action is in a consistent state.
> 
> Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>
> ---
>  fs/exec.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index d8af85f..8344fba 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1193,11 +1193,11 @@ static int unshare_sighand(struct task_struct *me)
>  			return -ENOMEM;
>  
>  		refcount_set(&newsighand->count, 1);
> -		memcpy(newsighand->action, oldsighand->action,
> -		       sizeof(newsighand->action));
>  
>  		write_lock_irq(&tasklist_lock);
>  		spin_lock(&oldsighand->siglock);
> +		memcpy(newsighand->action, oldsighand->action,
> +		       sizeof(newsighand->action));
>  		rcu_assign_pointer(me->sighand, newsighand);
>  		spin_unlock(&oldsighand->siglock);
>  		write_unlock_irq(&tasklist_lock);

Oh, yeah, that's a nice catch.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook