linux-kernel - Re: [PATCHv5 6/7] perf: introduce a flag to enable close-on-exec in perf_event

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Date:	Mon, 6 Jan 2014 10:29:29 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yann Droneaud <ydroneaud@...eya.com>
Cc:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv5 6/7] perf: introduce a flag to enable close-on-exec in
 perf_event_open()

On Sun, Jan 05, 2014 at 09:36:33PM +0100, Yann Droneaud wrote:
> Unlike recent modern userspace API such as
>   epoll_create1 (EPOLL_CLOEXEC), eventfd (EFD_CLOEXEC),
>   fanotify_init (FAN_CLOEXEC), inotify_init1 (IN_CLOEXEC),
>   signalfd (SFD_CLOEXEC), timerfd_create (TFD_CLOEXEC),
>   or the venerable general purpose open (O_CLOEXEC),
> perf_event_open() syscall lack a flag to atomically set FD_CLOEXEC
> (eg. close-on-exec) flag on file descriptor it returns to userspace.
> 
> The present patch adds a PERF_FLAG_FD_CLOEXEC flag to allow
> perf_event_open() syscall to atomically set close-on-exec.
> 
> Having this flag will enable userspace to remove the file descriptor
> from the list of file descriptors being inherited across exec,
> without the need to call fcntl(fd, F_SETFD, FD_CLOEXEC) and the
> associated race condition between the current thread and another
> thread calling fork(2) then execve(2).
> 
> Links:
> 
>  - Secure File Descriptor Handling (Ulrich Drepper, 2008)
>    http://udrepper.livejournal.com/20407.html
> 
>  - Excuse me son, but your code is leaking !!! (Dan Walsh, March 2012)
>    http://danwalsh.livejournal.com/53603.html
> 
>  - Notes in DMA buffer sharing: leak and security hole
>    http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/dma-buf-sharing.txt?id=v3.13-rc3#n428
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>

Seems sane enough.

Thanks!
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