linux-kernel - Re: [PATCH 3/3] exec: Rename the flag called_exec_mmap point_of_no

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Message-ID: <202004070903.CC08A70A@keescook>
Date:   Tue, 7 Apr 2020 09:03:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: Re: [PATCH 3/3] exec: Rename the flag called_exec_mmap
 point_of_no_return

On Mon, Apr 06, 2020 at 08:32:23PM -0500, Eric W. Biederman wrote:
> 
> Update the comments and make the code easier to understand by
> renaming this flag.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

I like it, yes!

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

-Kees

> ---
>  fs/exec.c               | 12 ++++++------
>  include/linux/binfmts.h |  6 +++---
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index 28c87020da9b..a61987d6dc33 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1300,12 +1300,12 @@ int flush_old_exec(struct linux_binprm * bprm)
>  		goto out;
>  
>  	/*
> -	 * After setting bprm->called_exec_mmap (to mark that current is
> -	 * using the prepared mm now), we have nothing left of the original
> -	 * process. If anything from here on returns an error, the check
> -	 * in search_binary_handler() will SEGV current.
> +	 * With the new mm installed it is completely impossible to
> +	 * fail and return to the original process.  If anything from
> +	 * here on returns an error, the check in
> +	 * search_binary_handler() will SEGV current.
>  	 */
> -	bprm->called_exec_mmap = 1;
> +	bprm->point_of_no_return = true;
>  	bprm->mm = NULL;
>  
>  #ifdef CONFIG_POSIX_TIMERS
> @@ -1694,7 +1694,7 @@ int search_binary_handler(struct linux_binprm *bprm)
>  
>  		read_lock(&binfmt_lock);
>  		put_binfmt(fmt);
> -		if (retval < 0 && bprm->called_exec_mmap) {
> +		if (retval < 0 && bprm->point_of_no_return) {
>  			/* we got to flush_old_exec() and failed after it */
>  			read_unlock(&binfmt_lock);
>  			force_sigsegv(SIGSEGV);
> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
> index 6f564b9ad882..8f479dad7931 100644
> --- a/include/linux/binfmts.h
> +++ b/include/linux/binfmts.h
> @@ -46,10 +46,10 @@ struct linux_binprm {
>  		 */
>  		secureexec:1,
>  		/*
> -		 * Set by flush_old_exec, when exec_mmap has been called.
> -		 * This is past the point of no return.
> +		 * Set when errors can no longer be returned to the
> +		 * original userspace.
>  		 */
> -		called_exec_mmap:1;
> +		point_of_no_return:1;
>  #ifdef __alpha__
>  	unsigned int taso:1;
>  #endif
> -- 
> 2.25.0
> 

-- 
Kees Cook