linux-kernel - Re: [PATCHv5 5/7] fanotify: enable close-on-exec on events' fd when requested in fanotify

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Date:	Mon, 20 Jan 2014 18:15:30 +0100
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Lino Sanfilippo <LinoSanfilippo@....de>
Cc:	linux-kernel@...r.kernel.org, Eric Paris <eparis@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv5 5/7] fanotify: enable close-on-exec on events' fd when
 requested in fanotify_init()

Hi Lino,

I've recently sent this patch which may fix a bug in the way fanotify
creates its file descriptors.

I failed to noticed you've been working recently on fanotify subsystem
and miss the opportunity to add you in the Cc:s. 

Please have a look to this patch and help to get it merged.

Le dimanche 05 janvier 2014 à 21:36 +0100, Yann Droneaud a écrit :
> According to commit 80af258867648, file descriptor created as part
> of file access notification events inherit flags from the event_f_flags
> argument passed to syscall fanotify_init(2).
> 
> So while it is legal for userspace to call fanotify_init() with O_CLOEXEC
> as part of its second argument, O_CLOEXEC is currently silently ignored.
> 
> Indeed event_f_flags are only given to dentry_open(), which only
> seems to care about O_ACCMODE and O_PATH in do_dentry_open(), O_DIRECT
> in open_check_o_direct() and O_LARGEFILE in generic_file_open().
> 
> More, there's no effective check on event_f_flags value that would
> catch unknown / unsupported values, unlike the one on f_flags argument
> of the syscall (see FAN_ALL_INIT_FLAGS in include/uapi/linux/fanotify.h).

...

> But it seems logical to set close-on-exec flag on the file descriptor
> if userspace is allowed to request it with O_CLOEXEC.
> 

...

> So this patch replaces call to macro get_unused_fd() by a call to
> function get_unused_fd_flags() with event_f_flags value as argument.
> This way O_CLOEXEC flag in the second argument of fanotify_init(2)
> syscall is interpreted so that close-on-exec get enabled.

...

> Cc: Eric Paris <eparis@...hat.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: stable@...r.kernel.org
> Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>
> Link:
> http://lkml.kernel.org/r/cover.1388952061.git.ydroneaud@opteya.com
> 
> ---
>  fs/notify/fanotify/fanotify_user.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 57d7c083cb4b..6d0eaabba02e 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -71,7 +71,7 @@ static int create_fd(struct fsnotify_group *group,
>  
>  	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
>  
> -	client_fd = get_unused_fd();
> +	client_fd = get_unused_fd_flags(group->fanotify_data.f_flags);
>  	if (client_fd < 0)
>  		return client_fd;
>  

Regards.

-- 
Yann Droneaud
OPTEYA



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