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

[Eric Sandeen <sandeen@sandeen.net>]

On 3/5/14, 11:02 AM, Christoph Hellwig 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.
> 
> I see the use after free, but I don't see how I would have introduced it
> in that commit.  Before that libxfs_iput already was freeing the inode
> through the cache code, now we do it directly.

Ok, sorry if I wrongly implicated that commit.

>> @@ -739,12 +738,6 @@ ili_done:
>>  	} else {
>>  		libxfs_iput(ip, 0);
>>  	}
>> -
>> -	if (ip->i_itemp)
>> -		kmem_zone_free(xfs_ili_zone, ip->i_itemp);
>> -	else
>> -		ASSERT(0);
>> -	ip->i_itemp = NULL;
>>  }
> 
> Seems like inode_item_done should call into inode_item_unlock, which
> factors the exact sequence we want into a nice helper.

Yeah, that does seem better!   Thanks for spotting that.

The difference when calling inode_item_unlock is a bit more zeroing-out:

        ip->i_transp = NULL;

        iip->ili_flags = 0;

I'm not sure of the implications of that offhand, TBH.

Dave, hold off on my commit I guess ;)

-Eric

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