Re: [RFC PATCH 1/2] ceph: add support for encrypted snapshot names
From: Xiubo Li
Date: Tue Mar 15 2022 - 03:29:25 EST
On 3/15/22 2:32 AM, Luís Henriques wrote:
Xiubo Li <xiubli@xxxxxxxxxx> 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@xxxxxxx>
---
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.
OK, you were right. However, I don't see a simple way around it. And I
don't think that adding a fscrypt new interface to copy an existent nonce
makes sense.
So, here's another possible option: instead of setting the
DCACHE_NOKEY_NAME flag, we could simply do d_invalidate(dentry) before
leaving ceph_mkdir (if we're creating an encrypted snapshot, of course).
Would this be acceptable?
I think there has one simple way. Just think about without setting the
fscrypt_auth for the '.snap' dir's inode, that is without your this
patch it works well.
That's because when we create a snapshot under '.snap' dir, since the
'.snap' dir related inode doesn't have the fscrypt_auth been filled, so
when creating a new inode for the snapshot it won't fill the
fscrypt_auth for the new inode. And then in the handle_reply() it can
fill the fscrypt auth as expected.
You can make sure that in the ceph_new_inode() just skip setting the
fscrypt_auth for the new inode if the parent dir is a snapdir, that is
'.snap/'. And this will just leave it to be filled in the handle_reply().
-- Xiubo
Cheers,