linux-kernel - Re: [RFC PATCH 1/2] ceph: add support for encrypted snapshot names

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Message-ID: <87wngw94hh.fsf@brahms.olymp>
Date:   Mon, 14 Mar 2022 11:07:54 +0000
From:   Luís Henriques <lhenriques@...e.de>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] ceph: add support for encrypted snapshot names

Xiubo Li <xiubli@...hat.com> writes:

> On 3/14/22 10:45 AM, Xiubo Li wrote:
>>
>> On 3/12/22 4:30 PM, Xiubo Li wrote:
>>>
>>> On 3/11/22 1:26 AM, Luís Henriques wrote:
>>>> Since filenames in encrypted directories are already encrypted and shown
>>>> as a base64-encoded string when the directory is locked, snapshot names
>>>> should show a similar behaviour.
>>>>
>>>> Signed-off-by: Luís Henriques <lhenriques@...e.de>
>>>> ---
>>>>   fs/ceph/dir.c   |  9 +++++++++
>>>>   fs/ceph/inode.c | 13 +++++++++++++
>>>>   2 files changed, 22 insertions(+)
>>>>
>>>> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
>>>> index 6df2a91af236..123e3b9c8161 100644
>>>> --- a/fs/ceph/dir.c
>>>> +++ b/fs/ceph/dir.c
>>>> @@ -1075,6 +1075,15 @@ static int ceph_mkdir(struct user_namespace
>>>> *mnt_userns, struct inode *dir,
>>>>           op = CEPH_MDS_OP_MKSNAP;
>>>>           dout("mksnap dir %p snap '%pd' dn %p\n", dir,
>>>>                dentry, dentry);
>>>> +        /*
>>>> +         * Encrypted snapshots require d_revalidate to force a
>>>> +         * LOOKUPSNAP to cleanup dcache
>>>> +         */
>>>> +        if (IS_ENCRYPTED(dir)) {
>>>> +            spin_lock(&dentry->d_lock);
>>>> +            dentry->d_flags |= DCACHE_NOKEY_NAME;
>>>
>>> I think this is not correct fix of this issue.
>>>
>>> Actually this dentry's name is a KEY NAME, which is human readable name.
>>>
>>> DCACHE_NOKEY_NAME means the base64_encoded names. This usually will be set
>>> when filling a new dentry if the directory is locked. If the directory is
>>> unlocked the directory inode will be set with the key.
>>>
>>> The root cause should be the snapshot's inode doesn't correctly set the
>>> encrypt stuff when you are reading from it.
>>>
>>> NOTE: when you are 'ls -l .snap/snapXXX' the snapXXX dentry name is correct,
>>> it's just corrupted for the file or directory names under snapXXX/.
>>>
>> When mksnap in ceph_mkdir() before sending the request out it will create a
>> new inode for the snapshot dentry and then will fill the ci->fscrypt_auth from
>> .snap's inode, please see ceph_mkdir()->ceph_new_inode().
>>
>> And in the mksnap request reply it will try to fill the ci->fscrypt_auth again
>> but failed because it was already filled. This time the auth info is from
>> .snap's parent dir from MDS side. In this patch in theory they should be the
>> same, but I am still not sure why when decrypting the dentry names in snapXXX
>> will fail.
>>
>> I just guess it possibly will depend on the inode number from the related
>> inode or something else. Before the request reply it seems the inode isn't set
>> the inode number ?
>>
> It should be the ci_nonce's problem.
>
> In the ceph_mkdir()->ceph_new_inode() it will generate a new random nonce and
> then setup the fscrypt context for the inode of .snap/snapXXX. But this context
> is not correct, because the context of .snap/snapXXX should always be inherit
> from .snap's parent, which will be sent from the MDS in the request reply.

Hmm, OK, let me look closer into this.  What you're saying makes sense and
you're probably right.  Thank you for the hints.

Cheers,
-- 
Luís

>
>
>> - Xiubo
>>
>>>
>>>> + spin_unlock(&dentry->d_lock);
>>>> +        }
>>>>       } else if (ceph_snap(dir) == CEPH_NOSNAP) {
>>>>           dout("mkdir dir %p dn %p mode 0%ho\n", dir, dentry, mode);
>>>>           op = CEPH_MDS_OP_MKDIR;
>>>> diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
>>>> index b573a0f33450..81d3d554d261 100644
>>>> --- a/fs/ceph/inode.c
>>>> +++ b/fs/ceph/inode.c
>>>> @@ -182,6 +182,19 @@ struct inode *ceph_get_snapdir(struct inode *parent)
>>>>       ci->i_rbytes = 0;
>>>>       ci->i_btime = ceph_inode(parent)->i_btime;
>>>>   +    /* if encrypted, just borrow fscrypt_auth from parent */
>>>> +    if (IS_ENCRYPTED(parent)) {
>>>> +        struct ceph_inode_info *pci = ceph_inode(parent);
>>>> +
>>>> +        ci->fscrypt_auth = kmemdup(pci->fscrypt_auth,
>>>> +                       pci->fscrypt_auth_len,
>>>> +                       GFP_KERNEL);
>>>> +        if (ci->fscrypt_auth) {
>>>> +            inode->i_flags |= S_ENCRYPTED;
>>>> +            ci->fscrypt_auth_len = pci->fscrypt_auth_len;
>>>> +        } else
>>>> +            dout("Failed to alloc memory for fscrypt_auth in snapdir\n");
>>>> +    }
>>>
>>> Here I think Jeff has already commented it in your last version, it should
>>> fail by returning NULL ?
>>>
>>> - Xiubo
>>>
>>>>       if (inode->i_state & I_NEW) {
>>>>           inode->i_op = &ceph_snapdir_iops;
>>>>           inode->i_fop = &ceph_snapdir_fops;
>>>>
>