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

Jeff Layton
2021-04-06T16:03:30Z

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?

> 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.

>
> > + 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>