Re: [PATCHv5 6/7] perf: introduce a flag to enable close-on-exec inperf_event_open()

From: Peter Zijlstra
Date: Mon Jan 06 2014 - 04:29:55 EST

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)
> - Excuse me son, but your code is leaking !!! (Dan Walsh, March 2012)
> - Notes in DMA buffer sharing: leak and security hole
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Yann Droneaud <ydroneaud@xxxxxxxxxx>

Seems sane enough.

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