linux-kernel - Re: [PATCH] ceph: fix mdsmap decode for v >= 17

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Date:   Sun, 30 Oct 2022 20:37:53 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Luís Henriques <lhenriques@...e.de>
Cc:     Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ceph: fix mdsmap decode for v >= 17


On 28/10/2022 17:05, Luís Henriques wrote:
> On Fri, Oct 28, 2022 at 09:28:37AM +0800, Xiubo Li wrote:
>> On 27/10/2022 23:28, Luís Henriques wrote:
>>> Commit d93231a6bc8a ("ceph: prevent a client from exceeding the MDS
>>> maximum xattr size") was merged before the corresponding MDS-side changes
>>> have been merged.  With the introduction of 'bal_rank_mask' in the mdsmap,
>>> the decoding of maps with v>=17 is now incorrect.  Fix this by skipping
>>> the 'bal_rank_mask' string decoding.
>>>
>>> Fixes: d93231a6bc8a ("ceph: prevent a client from exceeding the MDS maximum xattr size")
>>> Signed-off-by: Luís Henriques <lhenriques@...e.de>
>>> ---
>>> Hi!
>>>
>>> This inconsistency was introduced by ceph PR #43284; I think that, before
>>> picking this patch, we need to get PR #46357 merged to avoid new
>>> problems.
>>>
>>> Cheers,
>>> --
>>> Luís
>>>
>>>    fs/ceph/mdsmap.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/fs/ceph/mdsmap.c b/fs/ceph/mdsmap.c
>>> index 3fbabc98e1f7..fe4f1a6c3465 100644
>>> --- a/fs/ceph/mdsmap.c
>>> +++ b/fs/ceph/mdsmap.c
>>> @@ -379,6 +379,8 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end, bool msgr2)
>>>    		ceph_decode_skip_8(p, end, bad_ext);
>>>    		/* required_client_features */
>>>    		ceph_decode_skip_set(p, end, 64, bad_ext);
>>> +		/* bal_rank_mask */
>>> +		ceph_decode_skip_string(p, end, bad_ext);
>>>    		ceph_decode_64_safe(p, end, m->m_max_xattr_size, bad_ext);
>>>    	} else {
>>>    		/* This forces the usage of the (sync) SETXATTR Op */
>>>
>> Luis,
>>
>> Because the ceph PR #43284 will break kclient here and your xattr size patch
>> got merged long time ago, we should fix it in ceph. More detail please see
>> my comments in:
>>
>> https://github.com/ceph/ceph/pull/46357#issuecomment-1294290492
> OK, agreed.  I'll update this PR to try to fix it on the MDS side
> instead.  And let's try to have it merged as soon as possible to prevent
> further issues.

Sounds good!

- Xiubo


> Cheers,
> --
> Luís
>