On Thu, 31 May 2007 14:09:15 -0400
Ulrich Drepper <[email protected]> wrote:
> I've brought this topic up before but didn't provide a patch. Well, here
> we go again, this time with a patch. I even throw in a test program.
>
> The problem is as follows: in multi-threaded code (or more correctly: all
> code using clone() with CLONE_FILES) we have a race when exec'ing.
>
> thread #1 thread #2
>
> fd=open()
>
> fork + exec
>
> fcntl(fd,F_SETFD,FD_CLOEXEC)
>
> In some applications this can happen frequently. Take a web browser. One
> thread opens a file and another thread starts, say, an external PDF viewer.
> The result can even be a security issue if that open file descriptor refers
> to a sensitive file and the external program can somehow be tricked into
> using that descriptor.
>
> Just adding O_CLOEXEC support to open() doesn't solve the whole set of
> problems. There are other ways to create file descriptors (socket,
> epoll_create, Unix domain socket transfer, etc). These can and should
> be addressed separately though. open() is such an easy case that it makes
> not much sense putting the fix off.
>
> ...
>
> diff --git a/include/asm-generic/fcntl.h b/include/asm-generic/fcntl.h
> index c154b9d..b847741 100644
> --- a/include/asm-generic/fcntl.h
> +++ b/include/asm-generic/fcntl.h
> @@ -48,6 +48,9 @@
> #ifndef O_NOATIME
> #define O_NOATIME 01000000
> #endif
> +#ifndef O_CLOEXEC
> +#define O_CLOEXEC 02000000 /* set close_on_exec */
> +#endif
> #ifndef O_NDELAY
> #define O_NDELAY O_NONBLOCK
> #endif
This will break xtensa, because that architecture (and only that
architecture) doesn't include asm-generic/fcntl.h from asm/fcntl.h.
But let's leave this patch as-is: it's xtensa which needs fixing.
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