Re: [RFC PATCH v5 19/19] ceph: add fscrypt ioctls

Jeff Layton
2021-04-06T17:27:27Z

On Tue, 2021-04-06 at 17:24 +0100, Luis Henriques wrote:
> On Tue, Apr 06, 2021 at 12:03:27PM -0400, Jeff Layton wrote:
> > On Tue, 2021-04-06 at 16:38 +0100, Luis Henriques wrote:
> > > Hi Jeff!
> > >
> > > On Fri, Mar 26, 2021 at 01:32:27PM -0400, Jeff Layton wrote:
> > > > We gate most of the ioctls on MDS feature support. The exception is the
> > > > key removal and status functions that we still want to work if the MDS's
> > > > were to (inexplicably) lose the feature.
> > > >
> > > > For the set_policy ioctl, we take Fcx caps to ensure that nothing can
> > > > create files in the directory while the ioctl is running. That should
> > > > be enough to ensure that the "empty_dir" check is reliable.
> > > >
> > > > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > > > ---
> > > > fs/ceph/ioctl.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 94 insertions(+)
> > > >
> > > > diff --git a/fs/ceph/ioctl.c b/fs/ceph/ioctl.c
> > > > index 6e061bf62ad4..34b85bcfcfc7 100644
> > > > --- a/fs/ceph/ioctl.c
> > > > +++ b/fs/ceph/ioctl.c
> > > > @@ -6,6 +6,7 @@
> > > > #include "mds_client.h"
> > > > #include "ioctl.h"
> > > > #include <linux/ceph/striper.h>
> > > > +#include <linux/fscrypt.h>
> > > >
> > > > /*
> > > > * ioctls
> > > > @@ -268,8 +269,56 @@ static long ceph_ioctl_syncio(struct file *file)
> > > > return 0;
> > > > }
> > > >
> > > > +static int vet_mds_for_fscrypt(struct file *file)
> > > > +{
> > > > + int i, ret = -EOPNOTSUPP;
> > > > + struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(file_inode(file)->i_sb);
> > > > +
> > > > + mutex_lock(&mdsc->mutex);
> > > > + for (i = 0; i < mdsc->max_sessions; i++) {
> > > > + struct ceph_mds_session *s = mdsc->sessions[i];
> > > > +
> > > > + if (!s)
> > > > + continue;
> > > > + if (test_bit(CEPHFS_FEATURE_ALTERNATE_NAME, &s->s_features))
> > > > + ret = 0;
> > > > + break;
> > > > + }
> > > > + mutex_unlock(&mdsc->mutex);
> > > > + return ret;
> > > > +}
> > > > +
> > > > +static long ceph_set_encryption_policy(struct file *file, unsigned long arg)
> > > > +{
> > > > + int ret, got = 0;
> > > > + struct page *page = NULL;
> > > > + struct inode *inode = file_inode(file);
> > > > + struct ceph_inode_info *ci = ceph_inode(inode);
> > > > +
> > > > + ret = vet_mds_for_fscrypt(file);
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + /*
> > > > + * Ensure we hold these caps so that we _know_ that the rstats check
> > > > + * in the empty_dir check is reliable.
> > > > + */
> > > > + ret = ceph_get_caps(file, CEPH_CAP_FILE_SHARED, 0, -1, &got, &page);
> > > > + if (ret)
> > > > + return ret;
> > > > + if (page)
> > > > + put_page(page);
> > > > + ret = fscrypt_ioctl_set_policy(file, (const void __user *)arg);
> > > > + if (got)
> > > > + ceph_put_cap_refs(ci, got);
> > > > + return ret;
> > > > +}
> > > > +
> > > > long ceph_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > > > {
> > > > + int ret;
> > > > + struct ceph_inode_info *ci = ceph_inode(file_inode(file));
> > > > +
> > > > dout("ioctl file %p cmd %u arg %lu\n", file, cmd, arg);
> > > > switch (cmd) {
> > > > case CEPH_IOC_GET_LAYOUT:
> > > > @@ -289,6 +338,51 @@ long ceph_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> > > >
> > > > case CEPH_IOC_SYNCIO:
> > > > return ceph_ioctl_syncio(file);
> > > > +
> > > > + case FS_IOC_SET_ENCRYPTION_POLICY:
> > > > + return ceph_set_encryption_policy(file, arg);
> > > > +
> > > > + case FS_IOC_GET_ENCRYPTION_POLICY:
> > > > + ret = vet_mds_for_fscrypt(file);
> > > > + if (ret)
> > > > + return ret;
> > > > + return fscrypt_ioctl_get_policy(file, (void __user *)arg);
> > > > +
> > > > + case FS_IOC_GET_ENCRYPTION_POLICY_EX:
> > > > + ret = vet_mds_for_fscrypt(file);
> > > > + if (ret)
> > > > + return ret;
> > > > + return fscrypt_ioctl_get_policy_ex(file, (void __user *)arg);
> > > > +
> > > > + case FS_IOC_ADD_ENCRYPTION_KEY:
> > > > + ret = vet_mds_for_fscrypt(file);
> > > > + if (ret)
> > > > + return ret;
> > > > + atomic_inc(&ci->i_shared_gen);
> > >
> > > I've spent a few hours already looking at the bug I reported before, and I
> > > can't really understand this code. What does it mean to increment
> > > ->i_shared_gen at this point?
> > >
> > > The reason I'm asking is because it looks like the problem I'm seeing goes
> > > away if I remove this code. Here's what I'm doing/seeing:
> > >
> > > # mount ...
> > > # fscrypt unlock d
> > >
> > > -> 'd' dentry is eventually pruned at this point *if* ->i_shared_gen was
> > > incremented by the line above.
> > >
> > > # cat d/f
> > >
> > > -> when ceph_fill_inode() is executed, 'd' isn't *not* set as encrypted
> > > because both ci->i_xattrs.version and info->xattr_version are both
> > > set to 0.
> > >
> >
> > Interesting. That sounds like it might be the bug right there. "d"
> > should clearly have a fscrypt context in its xattrs at that point. If
> > the MDS isn't passing that back, then that could be a problem.
> >
> > I had a concern about that when I was developing this, and I *thought*
> > Zheng had assured us that the MDS will always pass along the xattr blob
> > in a trace. Maybe that's not correct?
>
> Hmm, that's what I thought too. I was hoping not having to go look at the
> MDS, but seems like I'll have to :-)
>

That'd be good, if possible.

> > > cat: d/f: No such file or directory
> > >
> > > I'm not sure anymore if the issue is on the client or on the MDS side.
> > > Before digging deeper, I wonder if this ring any bell. ;-)
> > >
> > >
> >
> > No, this is not something I've seen before.
> >
> > Dentries that live in a directory have a copy of the i_shared_gen of the
> > directory when they are instantiated. Bumping that value on a directory
> > should basically ensure that its child dentries end up invalidated,
> > which is what we want once we add the key to the directory. Once we add
> > a key, any old dentries in that directory are no longer valid.
> >
> > That said, I could certainly have missed some subtlety here.
>
> Great, thanks for clarifying. This should help me investigate a little
> bit more.
>
> [ And I'm also surprised you don't see this behaviour as it's very easy to
> reproduce. ]
>
>

It is odd... fwiw, I ran this for 5 mins or so and never saw a problem:

$ while [ $? -eq 0 ]; do sudo umount /mnt/crypt; sudo mount /mnt/crypt; fscrypt unlock --key=/home/jlayton/fscrypt-keyfile /mnt/crypt/d; cat /mnt/crypt/d/f; done

...do I need some other operations in between? Also, the cluster in this
case is Pacific. It's possible this is a result of changes since then if
you're on a vstart cluster or something.

$ sudo ./cephadm version
Using recent ceph image docker.io/ceph/ceph@sha256:9b04c0f15704c49591640a37c7adfd40ffad0a4b42fecb950c3407687cb4f29a
ceph version 16.2.0 (0c2054e95bcd9b30fdd908a79ac1d8bbc3394442) pacific (stable)

> > >
> > > > + ceph_dir_clear_ordered(file_inode(file));
> > > > + ceph_dir_clear_complete(file_inode(file));
> > > > + return fscrypt_ioctl_add_key(file, (void __user *)arg);
> > > > +
> > > > + case FS_IOC_REMOVE_ENCRYPTION_KEY:
> > > > + atomic_inc(&ci->i_shared_gen);
> > > > + ceph_dir_clear_ordered(file_inode(file));
> > > > + ceph_dir_clear_complete(file_inode(file));
> > > > + return fscrypt_ioctl_remove_key(file, (void __user *)arg);
> > > > +
> > > > + case FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS:
> > > > + atomic_inc(&ci->i_shared_gen);
> > > > + ceph_dir_clear_ordered(file_inode(file));
> > > > + ceph_dir_clear_complete(file_inode(file));
> > > > + return fscrypt_ioctl_remove_key_all_users(file, (void __user *)arg);
> > > > +
> > > > + case FS_IOC_GET_ENCRYPTION_KEY_STATUS:
> > > > + return fscrypt_ioctl_get_key_status(file, (void __user *)arg);
> > > > +
> > > > + case FS_IOC_GET_ENCRYPTION_NONCE:
> > > > + ret = vet_mds_for_fscrypt(file);
> > > > + if (ret)
> > > > + return ret;
> > > > + return fscrypt_ioctl_get_nonce(file, (void __user *)arg);
> > > > }
> > > >
> > > > return -ENOTTY;
> > > > --
> > > > 2.30.2
> > > >
> >
> > --
> > Jeff Layton <jlayton@kernel.org>
> >

--
Jeff Layton <jlayton@kernel.org>