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Date: Thu, 10 Dec 2015 16:48:56 -0700
From: Andreas Dilger <adilger@...ger.ca>
To: Theodore Ts'o <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
mhalcrow@...gle.com
Subject: Re: [PATCH v3 2/3] ext4 crypto: add ioctls to allow backup of encryption metadata
On Dec 10, 2015, at 8:04 AM, Theodore Ts'o <tytso@....edu> wrote:
>
> Add new ioctls which allow for the metadata of encrypted files (the
> filename and the crypto policy) to be backed up. We can restore the
> crypto policy, but for now we can't restore the encrypted filename
> because messing with encrypted directories directly while bypassing
> the VFS would get fairly tricky/nasty.
Instead of exposing these via ioctls, why not use virtual xattrs
(e.g. "trusted.crypt_meta" or similar) so that this can be backed
up and restored using a normal backup tool instead of basically
nothing that exists today.
For reading the ciphertext, do existing tools such as tar and rsync
allow reading with O_DIRECT with CIPHERTEXT_ACCESS? If not, one might
consider to allow normal reads w/o the file key to return the
ciphertext so that "tar --xattr" by some process with CAP_SYS_ADMIN
but out any keys could be used to backup and restore the ciphertext
in a sensible manner. That is no more risk than the same process
reading the blocks from the disk device directly, but would be a lot
more useful (i.e. it is practical to use normal backup tools for
encrypted files).
Cheers, Andreas
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> ---
> fs/ext4/crypto_key.c | 57 ++++++++++++++++++++++++++++++++++++++++++++-
> fs/ext4/ext4.h | 9 ++++++++
> fs/ext4/ext4_crypto.h | 8 +++++++
> fs/ext4/ioctl.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++
> fs/ext4/namei.c | 24 +++++++++++++++++++
> 5 files changed, 161 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c
> index c5882b3..039b22d 100644
> --- a/fs/ext4/crypto_key.c
> +++ b/fs/ext4/crypto_key.c
> @@ -14,7 +14,7 @@
> #include <linux/scatterlist.h>
> #include <uapi/linux/keyctl.h>
>
> -#include "ext4.h"
> +#include "ext4_jbd2.h"
> #include "xattr.h"
>
> static void derive_crypt_complete(struct crypto_async_request *req, int rc)
> @@ -270,3 +270,58 @@ int ext4_has_encryption_key(struct inode *inode)
>
> return (ei->i_crypt_info != NULL);
> }
> +
> +int ext4_get_encryption_metadata(struct inode *inode,
> + struct ext4_encrypted_metadata *mdata)
> +{
> + int res;
> +
> + if (mdata->len < sizeof(struct ext4_encryption_context))
> + return -EINVAL;
> +
> + res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
> + EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
> + &mdata->metadata, mdata->len);
> + if (res < 0)
> + return res;
> + mdata->len = res;
> + return 0;
> +}
> +
> +int ext4_set_encryption_metadata(struct inode *inode,
> + struct ext4_encrypted_metadata *mdata)
> +{
> + struct ext4_encryption_context *ctx;
> + handle_t *handle;
> + int res;
> +
> + if (mdata->len != sizeof(struct ext4_encryption_context))
> + return -EINVAL;
> + ctx = (struct ext4_encryption_context *) &mdata->metadata;
> + if (ctx->format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
> + return -EINVAL;
> +
> + res = ext4_convert_inline_data(inode);
> + if (res)
> + return res;
> +
> + handle = ext4_journal_start(inode, EXT4_HT_MISC,
> + ext4_jbd2_credits_xattr(inode));
> + if (IS_ERR(handle))
> + return PTR_ERR(handle);
> + res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
> + EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, ctx,
> + sizeof(struct ext4_encryption_context), 0);
> + if (res < 0)
> + goto errout;
> + ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
> + ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
> + res = ext4_mark_inode_dirty(handle, inode);
> + if (res)
> + EXT4_ERROR_INODE(inode, "Failed to mark inode dirty");
> + else
> + res = ext4_get_encryption_info(inode);
> +errout:
> + ext4_journal_stop(handle);
> + return res;
> +}
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index cf7a885..c569430 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -617,6 +617,9 @@ enum {
> #define EXT4_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct ext4_encryption_policy)
> #define EXT4_IOC_GET_ENCRYPTION_PWSALT _IOW('f', 20, __u8[16])
> #define EXT4_IOC_GET_ENCRYPTION_POLICY _IOW('f', 21, struct ext4_encryption_policy)
> +#define EXT4_IOC_GET_ENCRYPTION_METADATA _IOWR('f', 22, struct ext4_encrypted_metadata)
> +#define EXT4_IOC_SET_ENCRYPTION_METADATA _IOR('f', 23, struct ext4_encrypted_metadata)
> +#define EXT4_IOC_GET_ENCRYPTED_FILENAME _IOWR('f', 24, struct ext4_encrypted_metadata)
>
> #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
> /*
> @@ -2311,6 +2314,10 @@ static inline void ext4_fname_free_filename(struct ext4_filename *fname) { }
> void ext4_free_crypt_info(struct ext4_crypt_info *ci);
> void ext4_free_encryption_info(struct inode *inode, struct ext4_crypt_info *ci);
> int _ext4_get_encryption_info(struct inode *inode);
> +int ext4_set_encryption_metadata(struct inode *inode,
> + struct ext4_encrypted_metadata *mdata);
> +int ext4_get_encryption_metadata(struct inode *inode,
> + struct ext4_encrypted_metadata *mdata);
>
> #ifdef CONFIG_EXT4_FS_ENCRYPTION
> int ext4_has_encryption_key(struct inode *inode);
> @@ -2546,6 +2553,8 @@ extern int ext4_generic_delete_entry(handle_t *handle,
> int buf_size,
> int csum_size);
> extern int ext4_empty_dir(struct inode *inode);
> +extern int ext4_get_encrypted_filename(struct file *filp,
> + struct ext4_encrypted_metadata *mdata);
>
> /* resize.c */
> extern int ext4_group_add(struct super_block *sb,
> diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
> index ac7d4e8..f267cd3 100644
> --- a/fs/ext4/ext4_crypto.h
> +++ b/fs/ext4/ext4_crypto.h
> @@ -156,4 +156,12 @@ static inline u32 encrypted_symlink_data_len(u32 l)
> return (l + sizeof(struct ext4_encrypted_symlink_data) - 1);
> }
>
> +/**
> + * Structure used for communicating encrypted metadata with userspace
> + */
> +struct ext4_encrypted_metadata {
> + u32 len;
> + char metadata[288];
> +};
> +
> #endif /* _EXT4_CRYPTO_H */
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 5e872fd..afb51f5 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -689,6 +689,67 @@ encryption_policy_out:
> return -EOPNOTSUPP;
> #endif
> }
> + case EXT4_IOC_GET_ENCRYPTION_METADATA: {
> +#ifdef CONFIG_EXT4_FS_ENCRYPTION
> + struct ext4_encrypted_metadata mdata;
> + int err = 0;
> +
> + if (get_user(mdata.len, (u32 __user *) arg))
> + return -EFAULT;
> + if (mdata.len > sizeof(mdata.metadata))
> + return -EINVAL;
> +
> + if (!ext4_encrypted_inode(inode))
> + return -ENOENT;
> + err = ext4_get_encryption_metadata(inode, &mdata);
> + if (err)
> + return err;
> + if (copy_to_user((void __user *)arg, &mdata, sizeof(mdata)))
> + return -EFAULT;
> + return 0;
> +#else
> + return -EOPNOTSUPP;
> +#endif
> + }
> + case EXT4_IOC_SET_ENCRYPTION_METADATA: {
> +#ifdef CONFIG_EXT4_FS_ENCRYPTION
> + struct ext4_encrypted_metadata mdata;
> + int err = 0;
> +
> + if (ext4_encrypted_inode(inode))
> + return -EINVAL;
> + if (copy_from_user(&mdata,
> + (struct ext4_encrypted_metadata __user *)arg,
> + sizeof(mdata)))
> + return -EFAULT;
> + err = ext4_set_encryption_metadata(inode, &mdata);
> + return err;
> +#else
> + return -EOPNOTSUPP;
> +#endif
> + }
> + case EXT4_IOC_GET_ENCRYPTED_FILENAME: {
> +#ifdef CONFIG_EXT4_FS_ENCRYPTION
> + struct ext4_encrypted_metadata mdata;
> + int err = 0;
> +
> + if (get_user(mdata.len, (u32 __user *) arg))
> + return -EFAULT;
> + if (mdata.len > sizeof(mdata.metadata))
> + return -EINVAL;
> +
> + if (!ext4_encrypted_inode(inode))
> + return -ENOENT;
> + err = ext4_get_encrypted_filename(filp, &mdata);
> + if (err)
> + return err;
> + if (copy_to_user((void __user *)arg, &mdata, sizeof(mdata)))
> + return -EFAULT;
> + return 0;
> +#else
> + return -EOPNOTSUPP;
> +#endif
> + }
> default:
> return -ENOTTY;
> }
> @@ -755,6 +816,9 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> case EXT4_IOC_SET_ENCRYPTION_POLICY:
> case EXT4_IOC_GET_ENCRYPTION_PWSALT:
> case EXT4_IOC_GET_ENCRYPTION_POLICY:
> + case EXT4_IOC_GET_ENCRYPTION_METADATA:
> + case EXT4_IOC_SET_ENCRYPTION_METADATA:
> + case EXT4_IOC_GET_ENCRYPTED_FILENAME:
> break;
> default:
> return -ENOIOCTLCMD;
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index a969ab3..1cc4eef 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -3861,3 +3861,27 @@ const struct inode_operations ext4_special_inode_operations = {
> .get_acl = ext4_get_acl,
> .set_acl = ext4_set_acl,
> };
> +
> +int ext4_get_encrypted_filename(struct file *filp,
> + struct ext4_encrypted_metadata *mdata)
> +{
> + struct dentry *dentry = filp->f_path.dentry;
> + struct inode *dir = dentry->d_parent->d_inode;
> + struct buffer_head *bh;
> + struct ext4_dir_entry_2 *de;
> +
> + if (!dir || !ext4_encrypted_inode(dir))
> + return -EINVAL;
> +
> + bh = ext4_find_entry(dir, &dentry->d_name, &de, NULL);
> + if (IS_ERR(bh))
> + return PTR_ERR(bh);
> + if (de == NULL)
> + return -ENOENT;
> +
> + if (mdata->len < de->name_len)
> + return -ENOSPC;
> + mdata->len = de->name_len;
> + memcpy(mdata->metadata, de->name, de->name_len);
> + return 0;
> +}
> --
> 2.5.0
>
> --
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Cheers, Andreas
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