linux-kernel - Re: [BUG] fs: inotify_handle_event() reading un-init memory

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Message-ID: <20150617081319.GA1614@quack.suse.cz>
Date:	Wed, 17 Jun 2015 10:13:19 +0200
From:	Jan Kara <jack@...e.cz>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] fs: inotify_handle_event() reading un-init memory

On Tue 16-06-15 22:22:34, Jesper Dangaard Brouer wrote:
> 
> On Tue, 16 Jun 2015 15:52:09 +0200 Jan Kara <jack@...e.cz> wrote:
> 
> > On Tue 16-06-15 13:33:18, Jesper Dangaard Brouer wrote:
> > > Caught by kmemcheck.
> > > 
> > > Don't know the fix... just pointed at the bug.
> > > 
> > > Introduced in commit 7053aee26a3 ("fsnotify: do not share
> > > events between notification groups").
> > > ---
> > >  fs/notify/inotify/inotify_fsnotify.c |    3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
> > > index 2cd900c2c737..370d66dc4ddb 100644
> > > --- a/fs/notify/inotify/inotify_fsnotify.c
> > > +++ b/fs/notify/inotify/inotify_fsnotify.c
> > > @@ -96,11 +96,12 @@ int inotify_handle_event(struct fsnotify_group *group,
> > >  	i_mark = container_of(inode_mark, struct inotify_inode_mark,
> > >  			      fsn_mark);
> > >  
> > > +	// new object alloc here
> > >  	event = kmalloc(alloc_len, GFP_KERNEL);
> > >  	if (unlikely(!event))
> > >  		return -ENOMEM;
> > >  
> > > -	fsn_event = &event->fse;
> > > +	fsn_event = &event->fse; // This looks wrong!?! read from un-init mem?
> > 
> > Where is here any read? This is just a pointer arithmetics where we add
> > offset of 'fse' entry to 'event' address.
> 
> I was kmemcheck that complained, perhaps it is a false-positive?
  May be. What was the kmemcheck warning you saw? And can you also attach
disassembly of inotify_handle_event() from your kernel? Thanks!

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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