On Mon, 29 Sep 2014 10:49:15 +0200 Yann Droneaud <ydroneaud@xxxxxxxxxx> wrote:
> According to commit 80af258867648 ('fanotify: groups can specify
> their f_flags for new fd'), file descriptors 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().
>
> But it seems logical to set close-on-exec flag on the file
> descriptor if userspace is allowed to request it with O_CLOEXEC.
>
> In fact, according to some lookup on http://codesearch.debian.net/
> and various search engine, there's already some userspace code
> requesting it:
>
> - in systemd's readahead[2]:
>
> fanotify_fd = fanotify_init(FAN_CLOEXEC|FAN_NONBLOCK, O_RDONLY|O_LARGEFILE|O_CLOEXEC|O_NOATIME);
>
> - in clsync[3]:
>
> #define FANOTIFY_EVFLAGS (O_LARGEFILE|O_RDONLY|O_CLOEXEC)
>
> int fanotify_d = fanotify_init(FANOTIFY_FLAGS, FANOTIFY_EVFLAGS);
>
> - in examples [4] from "Filesystem monitoring in the Linux
> kernel" article[5] by Aleksander Morgado:
>
> if ((fanotify_fd = fanotify_init (FAN_CLOEXEC,
> O_RDONLY | O_CLOEXEC | O_LARGEFILE)) < 0)
So we have a number of apps which are setting O_CLOEXEC, but it doesn't
actually work. With this change it *will* work, so the behaviour of
those apps might change, possibly breaking them?
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