linux-kernel - Re: [PATCH] inotify: hide internal kernel bits from fdinfo

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Date:	Mon, 21 Sep 2015 22:28:49 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Dave Hansen <dave@...1.net>
Cc:	dave.hansen@...ux.intel.com, avagin@...il.com,
	akpm@...ux-foundation.org, xemul@...allels.com, eparis@...hat.com,
	john@...nmccutchan.com, rlove@...ve.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] inotify: hide internal kernel bits from fdinfo

On Mon, Sep 21, 2015 at 11:45:01AM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> There was a report that my patch:
> 
> 	inotify: actually check for invalid bits in sys_inotify_add_watch()
> 
> broke CRIU.
> 
> The reason is that CRIU looks up raw flags in /proc/$pid/fdinfo/*
> to figure out how to rebuild inotify watches and then passes those
> flags directly back in to the inotify API.  One of those flags
> (FS_EVENT_ON_CHILD) is set in mark->mask, but is not part of the
> inotify API.  It is used inside the kernel to _implement_ inotify
> but it is not and has never been part of the API.
> 
> My patch above ensured that we only allow bits which are part of
> the API (IN_ALL_EVENTS).  This broke CRIU.
> 
> FS_EVENT_ON_CHILD is really internal to the kernel.  It is set
> _anyway_ on all inotify marks.  So, CRIU was really just trying
> to set a bit that was already set.
> 
> This patch hides that bit from fdinfo.  CRIU will not see the
> bit, not try to set it, and should work as before.  We should not
> have been exposing this bit in the first place, so this is a good
> patch independent of the CRIU problem.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Reported-by: Andrey Wagin <avagin@...il.com>
Acked-by: Cyrill Gorcunov <gorcunov@...nvz.org>

Thank you!
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