Re: [PATCH 1/2] NFSD: Fix use-after-free warning when doing inter-server copy

dai.ngo
2021-02-21T04:17:33Z

On 2/20/21 6:08 AM, Olga Kornievskaia wrote:
> On Fri, Feb 19, 2021 at 10:21 PM J. Bruce Fields <bfields@fieldses.org> wrote:
>> On Fri, Feb 19, 2021 at 05:31:58PM -0800, dai.ngo@oracle.com wrote:
>>> If this is the cause why we don't drop the mount after the copy
>>> then I can restore the patch and look into this problem. Unfortunately,
>>> all my test machines are down for maintenance until Sunday/Monday.
>> I think we can take some time to figure out what's actually going on
>> here before reverting anything.
> Yes I agree. We need to fix the use-after-free and also make sure that
> reference will go away. I'm assuming to reproduce the use-after-free I
> need to run with kazan, is that what you did Dai?

I did not use Kasan. I just did an inter-server copy and this message
showed up in /var/log/messages.

-Dai

>
>> --b.
>>
>>> -Dai
>>>
>>> On 2/19/21 5:09 PM, J. Bruce Fields wrote:
>>>> Dai, do you have a copy of the original use-after-free warning?
>>>>
>>>> --b.
>>>>
>>>> On Fri, Feb 19, 2021 at 07:18:53PM -0500, Olga Kornievskaia wrote:
>>>>> Hi Dai (Bruce),
>>>>>
>>>>> This patch is what broke the mount that's now left behind between the
>>>>> source server and the destination server. We are no longer dropping
>>>>> the necessary reference on the mount to go away. I haven't been paying
>>>>> as much attention as I should have been to the changes. The original
>>>>> code called fput(src) so a simple refcount of the file. Then things
>>>>> got complicated and moved to nfsd_file_put(). So I don't understand
>>>>> complexity. But we need to do some kind of put to decrement the needed
>>>>> reference on the superblock. Bruce any ideas? Can we go back to
>>>>> fput()?
>>>>>
>>>>> On Thu, Oct 29, 2020 at 3:08 PM Dai Ngo <dai.ngo@oracle.com> wrote:
>>>>>> The source file nfsd_file is not constructed the same as other
>>>>>> nfsd_file's via nfsd_file_alloc. nfsd_file_put should not be
>>>>>> called to free the object; nfsd_file_put is not the inverse of
>>>>>> kzalloc, instead kfree is called by nfsd4_do_async_copy when done.
>>>>>>
>>>>>> Fixes: ce0887ac96d3 ("NFSD add nfs4 inter ssc to nfsd4_copy")
>>>>>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>>>>>> ---
>>>>>> fs/nfsd/nfs4proc.c | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
>>>>>> index ad2fa1a8e7ad..9c43cad7e408 100644
>>>>>> --- a/fs/nfsd/nfs4proc.c
>>>>>> +++ b/fs/nfsd/nfs4proc.c
>>>>>> @@ -1299,7 +1299,7 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct nfsd_file *src,
>>>>>> struct nfsd_file *dst)
>>>>>> {
>>>>>> nfs42_ssc_close(src->nf_file);
>>>>>> - nfsd_file_put(src);
>>>>>> + /* 'src' is freed by nfsd4_do_async_copy */
>>>>>> nfsd_file_put(dst);
>>>>>> mntput(ss_mnt);
>>>>>> }
>>>>>> --
>>>>>> 2.20.1.1226.g1595ea5.dirty
>>>>>>