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

dai.ngo
2021-02-20T01:33:07Z

Hi Olga and Bruce,

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.

-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
>>>