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Re: [PATCH 6/5]: XFS: Prevent use-after-free caused by synchronous inode

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 6/5]: XFS: Prevent use-after-free caused by synchronous inode reclaim
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 9 Oct 2008 19:07:41 +1100
Cc: xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
In-reply-to: <20081009070245.GA16621@xxxxxxxxxxxxx>
Mail-followup-to: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
References: <1223416332-7026-1-git-send-email-david@xxxxxxxxxxxxx> <20081009042134.GD9597@disturbed> <20081009070245.GA16621@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Thu, Oct 09, 2008 at 03:02:45AM -0400, Christoph Hellwig wrote:
> On Thu, Oct 09, 2008 at 03:21:34PM +1100, Dave Chinner wrote:
> > Folks,
> > 
> > The following patch fixes a use after free I just found.
> > It appears that switching between SLAB and SLUB seems to
> > turn off slab/slub memory poisoning, so i d??dn't realise
> > I'd be running for some time without poisoning turned on.
> > Once I turned poisoning back on I found this use-after-free
> > immediately on the first unmount trying to reclaim a clean
> > realtime bitmap inode.
> > 
> > With this patch, the netire patchset that I posted yesterday
> > passes xfsqa with memory poisoning turned on.
> 
> Looks good.
> 
> > +   XFS_STATS_INC(vn_reclaim);
> > +   if (xfs_reclaim(ip))
> > +           panic("%s: cannot reclaim 0x%p\n", __func__, inode);
> 
> Eventually we should kill the return value from xfs_reclaim and just put
> an assert directly into it.  In fact given that xfs_reclaim is quite
> OS dependent we might just merge the content directly into
> destroy_inode.

Yeah, I was thinking of doing exactly that in this patch, but I
figured that I'd just do the minimum needed to fix the bug because
we're getting close to the next merge window.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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