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Re: [PATCH] xfsprogs: fix use after free in inode_item_done()

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfsprogs: fix use after free in inode_item_done()
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Mon, 03 Mar 2014 16:48:29 -0600
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140303223617.GL13647@dastard>
References: <5314E912.9080708@xxxxxxxxxx> <20140303223617.GL13647@dastard>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.3.0
On 3/3/14, 4:36 PM, Dave Chinner wrote:
> On Mon, Mar 03, 2014 at 02:41:54PM -0600, Eric Sandeen wrote:
>> Commit "3a19fb7 libxfs: stop caching inode structures"
>> introduced a use after free.
>> libxfs_iput() already does the check for ip->i_itemp, and a
>> kmem_zone_free() if it's present, and then frees the ip pointer.
>> Re-checking ip->i_itemp after the libxfs_iput call will access
>> the freed ip pointer, as will setting ip_>i_itemp to NULL.
>> Simply remove the offending code to fix this up.
> which leaves the rest of the ili_done: code looking a little
> strange.
> can you convert that now to be:
> ili_done:
>       if (iip->ili_lock_flags) {
>               iip->ili_lock_flags = 0;
>               return;
>       }
>       /* free the inode */
>       libxfs_iput(ip, 0);
> }

yeah, I actually had that first.  Not sure why I didn't go with it ;)

(Still looks strange to my untrained eye; "if lock flags are set, unset them 
and don't free the inode, otherwise free it")

Anyway, I'll resend.  No need to educate me on these details, for now.  ;)


> Cheers,
> Dave.

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