Re: [RFC PATCH v3 14/16] ceph: add support to readdir for encrypted filenames

Eric Biggers
2020-09-15T01:57:24Z

On Mon, Sep 14, 2020 at 03:17:05PM -0400, Jeff Layton wrote:
> Add helper functions for buffer management and for decrypting filenames
> returned by the MDS. Wire those into the readdir codepaths.
>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
> fs/ceph/crypto.c | 47 +++++++++++++++++++++++++++++++++++++++
> fs/ceph/crypto.h | 35 +++++++++++++++++++++++++++++
> fs/ceph/dir.c | 58 +++++++++++++++++++++++++++++++++++++++---------
> fs/ceph/inode.c | 31 +++++++++++++++++++++++---
> 4 files changed, 157 insertions(+), 14 deletions(-)
>
> diff --git a/fs/ceph/crypto.c b/fs/ceph/crypto.c
> index f037a4939026..e3038c88c7a0 100644
> --- a/fs/ceph/crypto.c
> +++ b/fs/ceph/crypto.c
> @@ -107,3 +107,50 @@ int ceph_fscrypt_prepare_context(struct inode *dir, struct inode *inode,
> ceph_pagelist_release(pagelist);
> return ret;
> }
> +
> +int ceph_fname_to_usr(struct inode *parent, char *name, u32 len,
> + struct fscrypt_str *tname, struct fscrypt_str *oname,
> + bool *is_nokey)
> +{
> + int ret, declen;
> + u32 save_len;
> + struct fscrypt_str myname = FSTR_INIT(NULL, 0);
> +
> + if (!IS_ENCRYPTED(parent)) {
> + oname->name = name;
> + oname->len = len;
> + return 0;
> + }
> +
> + ret = fscrypt_get_encryption_info(parent);
> + if (ret)
> + return ret;
> +
> + if (tname) {
> + save_len = tname->len;
> + } else {
> + int err;
> +
> + save_len = 0;
> + err = fscrypt_fname_alloc_buffer(NAME_MAX, &myname);
> + if (err)
> + return err;
> + tname = &myname;

The 'err' variable isn't needed, since 'ret' can be used instead.

> + }
> +
> + declen = fscrypt_base64_decode(name, len, tname->name);
> + if (declen < 0 || declen > NAME_MAX) {
> + ret = -EIO;
> + goto out;
> + }

declen <= 0, to cover the empty name case.

Also, is there a point in checking for > NAME_MAX?

> +
> + tname->len = declen;
> +
> + ret = fscrypt_fname_disk_to_usr(parent, 0, 0, tname, oname, is_nokey);
> +
> + if (save_len)
> + tname->len = save_len;

This logic for temporarily overwriting the length is weird.
How about something like the following instead:

int ceph_fname_to_usr(struct inode *parent, char *name, u32 len,
struct fscrypt_str *tname, struct fscrypt_str *oname,
bool *is_nokey)
{
int err, declen;
struct fscrypt_str _tname = FSTR_INIT(NULL, 0);
struct fscrypt_str iname;

if (!IS_ENCRYPTED(parent)) {
oname->name = name;
oname->len = len;
return 0;
}

err = fscrypt_get_encryption_info(parent);
if (err)
return err;

if (!tname) {
err = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
if (err)
return err;
tname = &_tname;
}

declen = fscrypt_base64_decode(name, len, tname->name);
if (declen <= 0) {
err = -EIO;
goto out;
}

iname.name = tname->name;
iname.len = declen;
err = fscrypt_fname_disk_to_usr(parent, 0, 0, &iname, oname, is_nokey);
out:
fscrypt_fname_free_buffer(&_tname);
return err;
}