From: Eric Biggers <ebiggers@kernel.org>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-mtd@lists.infradead.org, linux-api@vger.kernel.org,
linux-crypto@vger.kernel.org, keyrings@vger.kernel.org,
Paul Crowley <paulcrowley@google.com>,
Satya Tangirala <satyat@google.com>
Subject: Re: [PATCH v7 10/16] fscrypt: v2 encryption policy support
Date: Mon, 29 Jul 2019 13:46:28 -0700 [thread overview]
Message-ID: <20190729204627.GH169027@gmail.com> (raw)
In-Reply-To: <20190728211730.GK6088@mit.edu>
On Sun, Jul 28, 2019 at 05:17:30PM -0400, Theodore Y. Ts'o wrote:
> On Fri, Jul 26, 2019 at 03:41:35PM -0700, Eric Biggers wrote:
> > @@ -319,6 +329,31 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
> > if (!capable(CAP_SYS_ADMIN))
> > goto out_wipe_secret;
> >
> > + if (arg.key_spec.type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) {
>
> This should be "== FSCRYPT_KEY_SPEC_TYPE_INDENTIFIER" instead. That's
> because you use the identifier part of the union:
>
> > + /* Calculate the key identifier and return it to userspace. */
> > + err = fscrypt_hkdf_expand(&secret.hkdf,
> > + HKDF_CONTEXT_KEY_IDENTIFIER,
> > + NULL, 0, arg.key_spec.u.identifier,
>
> If we ever add a new key specifier type, and alternative in the union,
> this is going to come back to bite us.
Well, I did it this way because the next patch changes the code to:
if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) {
...
} else {
...
}
We already validated that it's either TYPE_DESCRIPTOR or TYPE_IDENTIFIER.
But I guess to be more clear I'll just make it handle the default case again.
switch (arg.key_spec.type) {
case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
...
break;
case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
...
break;
default:
err = -EINVAL;
break;
}
>
> > + if (policy->version == FSCRYPT_POLICY_V1) {
> > + /*
> > + * The original encryption policy version provided no way of
> > + * verifying that the correct master key was supplied, which was
> > + * insecure in scenarios where multiple users have access to the
> > + * same encrypted files (even just read-only access).
>
> Which scenario do you have in mind? With read-only access, Alice can
> fetch the encryption policy for a directory, and introduce a key with
> the same descriptor, but the "wrong" key, but that's only going to
> affect Alice's use of the key. It won't affect what key is used by
> Bob, since Alice doesn't have write access to Bob's keyrings.
>
> If what you mean is the risk when there is a single global
> filesystem-specific keyring, where Alice could introduce a "wrong" key
> identified with a specific descriptor, then sure, Alice could trick
> Bob into encrypting his data with the wrong key (one known to Alice).
> But we don't allow keys usable by V1 policies to be used in the
> filesystem-specific keyring, do we?
>
The scenario is that Alice lists the directory with the wrong key, then Bob
lists the directory too and gets the wrong filenames. This happens because the
inode, fscrypt_info, dentry cache, page cache, etc. are the same for everyone.
Bob's key is never looked up because the inode already has a key cached.
This also applies to regular files and symlinks.
- Eric
next prev parent reply other threads:[~2019-07-29 20:46 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 22:41 [PATCH v7 00/16] fscrypt: key management improvements Eric Biggers
2019-07-26 22:41 ` [PATCH v7 01/16] fs, fscrypt: move uapi definitions to new header <linux/fscrypt.h> Eric Biggers
2019-07-28 15:08 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 02/16] fscrypt: use FSCRYPT_ prefix for uapi constants Eric Biggers
2019-07-26 22:41 ` [PATCH v7 03/16] fscrypt: use FSCRYPT_* definitions, not FS_* Eric Biggers
2019-07-26 22:41 ` [PATCH v7 04/16] fscrypt: add ->ci_inode to fscrypt_info Eric Biggers
2019-07-28 15:09 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 05/16] fscrypt: refactor v1 policy key setup into keysetup_legacy.c Eric Biggers
2019-07-28 15:40 ` Theodore Y. Ts'o
2019-07-29 19:37 ` Eric Biggers
2019-07-26 22:41 ` [PATCH v7 06/16] fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl Eric Biggers
2019-07-28 18:50 ` Theodore Y. Ts'o
2019-07-29 19:46 ` Eric Biggers
2019-07-29 20:14 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 07/16] fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl Eric Biggers
2019-07-28 19:24 ` Theodore Y. Ts'o
2019-07-29 19:58 ` Eric Biggers
2019-07-31 18:38 ` Eric Biggers
2019-07-31 23:38 ` Theodore Y. Ts'o
2019-08-01 1:11 ` [f2fs-dev] " Eric Biggers
2019-08-01 5:31 ` Theodore Y. Ts'o
2019-08-01 18:35 ` Eric Biggers
2019-08-01 18:46 ` Eric Biggers
2019-08-01 22:04 ` Eric Biggers
2019-08-02 4:38 ` Eric Biggers
2019-08-12 14:16 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 08/16] fscrypt: add FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl Eric Biggers
2019-07-28 19:30 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 09/16] fscrypt: add an HKDF-SHA512 implementation Eric Biggers
2019-07-28 19:39 ` Theodore Y. Ts'o
2019-07-29 20:29 ` Eric Biggers
2019-07-29 21:42 ` James Bottomley
2019-07-26 22:41 ` [PATCH v7 10/16] fscrypt: v2 encryption policy support Eric Biggers
2019-07-28 21:17 ` Theodore Y. Ts'o
2019-07-29 20:46 ` Eric Biggers [this message]
2019-07-26 22:41 ` [PATCH v7 11/16] fscrypt: allow unprivileged users to add/remove keys for v2 policies Eric Biggers
2019-07-28 21:22 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 12/16] fscrypt: require that key be added when setting a v2 encryption policy Eric Biggers
2019-07-28 21:24 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 13/16] ext4: wire up new fscrypt ioctls Eric Biggers
2019-07-28 21:24 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 14/16] f2fs: " Eric Biggers
2019-07-30 0:36 ` Jaegeuk Kim
2019-08-02 8:10 ` Chao Yu
2019-08-02 17:31 ` Eric Biggers
2019-08-04 9:42 ` [f2fs-dev] " Chao Yu
2019-07-26 22:41 ` [PATCH v7 15/16] ubifs: " Eric Biggers
2019-07-30 0:39 ` Theodore Y. Ts'o
2019-07-26 22:41 ` [PATCH v7 16/16] fscrypt: document the new ioctls and policy version Eric Biggers
2019-07-29 2:00 ` Theodore Y. Ts'o
2019-07-29 21:36 ` Eric Biggers
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