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

Luis Henriques
2021-04-06T15:37:35Z

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.

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. ;-)

Cheers,
--
Luís

> + 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
>