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

To: xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH 6/5]: XFS: Prevent use-after-free caused by synchronous inode reclaim
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 9 Oct 2008 03:02:45 -0400
In-reply-to: <20081009042134.GD9597@disturbed>
References: <1223416332-7026-1-git-send-email-david@xxxxxxxxxxxxx> <20081009042134.GD9597@disturbed>
User-agent: Mutt/1.5.18 (2008-05-17)
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.

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