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Date:   Tue, 10 Mar 2020 13:17:56 -0700
From:   Kees Cook <keescook@chromium.org>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Bernd Edlinger <bernd.edlinger@hotmail.de>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrei Vagin <avagin@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Yuyang Du <duyuyang@gmail.com>,
        David Hildenbrand <david@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        David Howells <dhowells@redhat.com>,
        James Morris <jamorris@linux.microsoft.com>,
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        Christian Kellner <christian@kellner.me>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
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Subject: Re: [PATCH v2 1/5] exec: Only compute current once in flush_old_exec
Message-ID: <202003101317.20BD018D9@keescook>
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On Sun, Mar 08, 2020 at 04:35:26PM -0500, Eric W. Biederman wrote:
> 
> Make it clear that current only needs to be computed once in
> flush_old_exec.  This may have some efficiency improvements and it
> makes the code easier to change.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

modulo my suggestion of adding more comments (it could even be kerndoc!)
that explicitly states that "me" should always be "current", yup, looks
good:

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

-Kees

> ---
>  fs/exec.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index db17be51b112..c3f34791f2f0 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1260,13 +1260,14 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
>   */
>  int flush_old_exec(struct linux_binprm * bprm)
>  {
> +	struct task_struct *me = current;
>  	int retval;
>  
>  	/*
>  	 * Make sure we have a private signal table and that
>  	 * we are unassociated from the previous thread group.
>  	 */
> -	retval = de_thread(current);
> +	retval = de_thread(me);
>  	if (retval)
>  		goto out;
>  
> @@ -1294,10 +1295,10 @@ int flush_old_exec(struct linux_binprm * bprm)
>  	bprm->mm = NULL;
>  
>  	set_fs(USER_DS);
> -	current->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
> +	me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
>  					PF_NOFREEZE | PF_NO_SETAFFINITY);
>  	flush_thread();
> -	current->personality &= ~bprm->per_clear;
> +	me->personality &= ~bprm->per_clear;
>  
>  	/*
>  	 * We have to apply CLOEXEC before we change whether the process is
> @@ -1305,7 +1306,7 @@ int flush_old_exec(struct linux_binprm * bprm)
>  	 * trying to access the should-be-closed file descriptors of a process
>  	 * undergoing exec(2).
>  	 */
> -	do_close_on_exec(current->files);
> +	do_close_on_exec(me->files);
>  	return 0;
>  
>  out:
> -- 
> 2.25.0
> 

-- 
Kees Cook