Messages in this thread Patch in this message | | | From | Yann Droneaud <> | Subject | [PATCHv8.2] fanotify: enable close-on-exec on events' fd when requested in fanotify_init() | Date | Fri, 3 Oct 2014 10:39:37 +0200 |
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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)[1].
Unfortunately 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().
It's a pity, since, according to some lookup on various search engines and http://codesearch.debian.net/, there's already some userspace code which use O_CLOEXEC:
- 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)
Additionally, since commit 48149e9d3a7e ('fanotify: check file flags passed in fanotify_init'). having O_CLOEXEC as part of fanotify_init() second argument is expressly allowed.
So it seems expected to set close-on-exec flag on the file descriptors if userspace is allowed to request it with O_CLOEXEC.
But Andrew Morton raised[6] the concern that enabling now close-on-exec might break existing applications which ask for O_CLOEXEC but expect the file descriptor to be inherited across exec().
In the other hand, as reported by Mihai Donțu[7], not setting close-on-exec on the file descriptor returned as part of file access notify can break applications due to deadlock. So close-on-exec is needed for most applications.
More, applications asking for close-on-exec are likely expecting it to be enabled, relying on O_CLOEXEC being effective. If not, it might weaken their security, as noted by Jan Kara[8].
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 and close-on-exec get enabled when requested.
[1] http://man7.org/linux/man-pages/man2/fanotify_init.2.html [2] http://cgit.freedesktop.org/systemd/systemd/tree/src/readahead/readahead-collect.c?id=v208#n294 [3] https://github.com/xaionaro/clsync/blob/v0.2.1/sync.c#L1631 https://github.com/xaionaro/clsync/blob/v0.2.1/configuration.h#L38 [4] http://www.lanedo.com/~aleksander/fanotify/fanotify-example.c [5] http://www.lanedo.com/2013/filesystem-monitoring-linux-kernel/ [6] http://lkml.kernel.org/r/20141001153621.65e9258e65a6167bf2e4cb50@linux-foundation.org [7] http://lkml.kernel.org/r/20141002095046.3715eb69@mdontu-l [8] http://lkml.kernel.org/r/20141002104410.GB19748@quack.suse.cz
Link: http://lkml.kernel.org/r/cover.1411562410.git.ydroneaud@opteya.com Cc: Mihai Donțu <mihai.dontu@gmail.com> Cc: Pádraig Brady <P@draigBrady.com> Cc: Heinrich Schuchardt <xypron.glpk@gmx.de> Cc: Jan Kara <jack@suse.cz> Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Cc: Michael Kerrisk-manpages <mtk.manpages@gmail.com> Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de> Cc: Richard Guy Briggs <rgb@redhat.com> Cc: Eric Paris <eparis@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: stable@vger.kernel.org Cc: linux-api@vger.kernel.org Reviewed-by: Jan Kara <jack@suse.cz> Reviewed by: Heinrich Schuchardt <xypron.glpk@gmx.de> Tested-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Signed-off-by: Yann Droneaud <ydroneaud@opteya.com> --- Hi Andrew,
> Fair enough, it sounds like the risk is acceptable. >
OK.
> Can we get a new version sent out with all this new info appropriately > changelogged? >
Of course !
Please find an updated patch with revamped commit message.
Changes from v8.1:
- added more Cc: - added Reviewed-by: - rewrote commit message.
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 b13992a41bd9..c991616acca9 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -78,7 +78,7 @@ 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; -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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