[RFC PATCH v9 10/16] dm-verity: consume root hash digest and signature data via LSM hook
Roberto Sassu
roberto.sassu at huaweicloud.com
Tue Jan 31 13:22:01 UTC 2023
On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote:
> From: Deven Bowers <deven.desai at linux.microsoft.com>
>
> dm-verity provides a strong guarantee of a block device's integrity. As
> a generic way to check the integrity of a block device, it provides
> those integrity guarantees to its higher layers, including the filesystem
> level.
I think you could reuse most of is_trusted_verity_target(), in
particular dm_verity_get_root_digest().
And probably, the previous patch is not necessary.
Roberto
> An LSM that control access to a resource on the system based on the
> available integrity claims can use this transitive property of
> dm-verity, by querying the underlying block_device of a particular
> file.
>
> The digest and signature information need to be stored in the block
> device to fulfill the next requirement of authorization via LSM policy.
> This will enable the LSM to perform revocation of devices that are still
> mounted, prohibiting execution of files that are no longer authorized
> by the LSM in question.
>
> Signed-off-by: Deven Bowers <deven.desai at linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan at linux.microsoft.com>
> ---
> v2:
> + No Changes
>
> v3:
> + No changes
>
> v4:
> + No changes
>
> v5:
> + No changes
>
> v6:
> + Fix an improper cleanup that can result in
> a leak
>
> v7:
> + Squash patch 08/12, 10/12 to [11/16]
> + Use part0 for block_device, to retrieve the block_device, when
> calling security_bdev_setsecurity
>
> v8:
> + Undo squash of 08/12, 10/12 - separating drivers/md/ from
> security/ & block/
> + Use common-audit function for dmverity_signature.
> + Change implementation for storing the dm-verity digest to use the
> newly introduced dm_verity_digest structure introduced in patch
> 14/20.
> + Create new structure, dm_verity_digest, containing digest algorithm,
> size, and digest itself to pass to the LSM layer. V7 was missing the
> algorithm.
> + Create an associated public header containing this new structure and
> the key values for the LSM hook, specific to dm-verity.
> + Additional information added to commit, discussing the layering of
> the changes and how the information passed will be used.
>
> v9:
> + No changes
> ---
> drivers/md/dm-verity-target.c | 25 +++++++++++++++++++++++--
> drivers/md/dm-verity-verify-sig.c | 16 +++++++++++++---
> drivers/md/dm-verity-verify-sig.h | 10 ++++++----
> include/linux/dm-verity.h | 19 +++++++++++++++++++
> 4 files changed, 61 insertions(+), 9 deletions(-)
> create mode 100644 include/linux/dm-verity.h
>
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index ccf5b852fbf7..afea61eed4ec 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -13,6 +13,7 @@
> * access behavior.
> */
>
> +#include "dm-core.h"
> #include "dm-verity.h"
> #include "dm-verity-fec.h"
> #include "dm-verity-verify-sig.h"
> @@ -21,6 +22,9 @@
> #include <linux/scatterlist.h>
> #include <linux/string.h>
> #include <linux/jump_label.h>
> +#include <linux/security.h>
> +#include <linux/dm-verity.h>
> +#include <crypto/hash_info.h>
>
> #define DM_MSG_PREFIX "verity"
>
> @@ -1169,6 +1173,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> sector_t hash_position;
> char dummy;
> char *root_hash_digest_to_validate;
> + struct block_device *bdev;
> + struct dm_verity_digest root_digest;
>
> v = kzalloc(sizeof(struct dm_verity), GFP_KERNEL);
> if (!v) {
> @@ -1211,6 +1217,13 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> }
> v->version = num;
>
> + bdev = dm_table_get_md(ti->table)->disk->part0;
> + if (!bdev) {
> + ti->error = "Mapped device lookup failed";
> + r = -ENOMEM;
> + goto bad;
> + }
> +
> r = dm_get_device(ti, argv[1], FMODE_READ, &v->data_dev);
> if (r) {
> ti->error = "Data device lookup failed";
> @@ -1343,7 +1356,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> }
>
> /* Root hash signature is a optional parameter*/
> - r = verity_verify_root_hash(root_hash_digest_to_validate,
> + r = verity_verify_root_hash(bdev, root_hash_digest_to_validate,
> strlen(root_hash_digest_to_validate),
> verify_args.sig,
> verify_args.sig_size);
> @@ -1428,12 +1441,20 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> ti->per_io_data_size = roundup(ti->per_io_data_size,
> __alignof__(struct dm_verity_io));
>
> + root_digest.digest = v->root_digest;
> + root_digest.digest_len = v->digest_size;
> + root_digest.algo = v->alg_name;
> +
> + r = security_bdev_setsecurity(bdev, DM_VERITY_ROOTHASH_SEC_NAME, &root_digest,
> + sizeof(root_digest));
> + if (r)
> + goto bad;
> +
> verity_verify_sig_opts_cleanup(&verify_args);
>
> return 0;
>
> bad:
> -
> verity_verify_sig_opts_cleanup(&verify_args);
> verity_dtr(ti);
>
> diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c
> index db61a1f43ae9..5a73b91157d5 100644
> --- a/drivers/md/dm-verity-verify-sig.c
> +++ b/drivers/md/dm-verity-verify-sig.c
> @@ -9,6 +9,9 @@
> #include <linux/verification.h>
> #include <keys/user-type.h>
> #include <linux/module.h>
> +#include <linux/security.h>
> +#include <linux/dm-verity.h>
> +#include "dm-core.h"
> #include "dm-verity.h"
> #include "dm-verity-verify-sig.h"
>
> @@ -97,14 +100,17 @@ int verity_verify_sig_parse_opt_args(struct dm_arg_set *as,
> * verify_verify_roothash - Verify the root hash of the verity hash device
> * using builtin trusted keys.
> *
> + * @bdev: block_device representing the device-mapper created block device.
> + * Used by the security hook, to set information about the block_device.
> * @root_hash: For verity, the roothash/data to be verified.
> * @root_hash_len: Size of the roothash/data to be verified.
> * @sig_data: The trusted signature that verifies the roothash/data.
> * @sig_len: Size of the signature.
> *
> */
> -int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
> - const void *sig_data, size_t sig_len)
> +int verity_verify_root_hash(struct block_device *bdev, const void *root_hash,
> + size_t root_hash_len, const void *sig_data,
> + size_t sig_len)
> {
> int ret;
>
> @@ -126,8 +132,12 @@ int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
> NULL,
> #endif
> VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL);
> + if (ret)
> + return ret;
>
> - return ret;
> + return security_bdev_setsecurity(bdev,
> + DM_VERITY_SIGNATURE_SEC_NAME,
> + sig_data, sig_len);
> }
>
> void verity_verify_sig_opts_cleanup(struct dm_verity_sig_opts *sig_opts)
> diff --git a/drivers/md/dm-verity-verify-sig.h b/drivers/md/dm-verity-verify-sig.h
> index 3987c7141f79..31692fff92e4 100644
> --- a/drivers/md/dm-verity-verify-sig.h
> +++ b/drivers/md/dm-verity-verify-sig.h
> @@ -20,8 +20,9 @@ struct dm_verity_sig_opts {
>
> #define DM_VERITY_ROOT_HASH_VERIFICATION_OPTS 2
>
> -int verity_verify_root_hash(const void *data, size_t data_len,
> - const void *sig_data, size_t sig_len);
> +int verity_verify_root_hash(struct block_device *bdev, const void *data,
> + size_t data_len, const void *sig_data,
> + size_t sig_len);
> bool verity_verify_is_sig_opt_arg(const char *arg_name);
>
> int verity_verify_sig_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
> @@ -34,8 +35,9 @@ void verity_verify_sig_opts_cleanup(struct dm_verity_sig_opts *sig_opts);
>
> #define DM_VERITY_ROOT_HASH_VERIFICATION_OPTS 0
>
> -static inline int verity_verify_root_hash(const void *data, size_t data_len,
> - const void *sig_data, size_t sig_len)
> +int verity_verify_root_hash(struct block_device *bdev, const void *data,
> + size_t data_len, const void *sig_data,
> + size_t sig_len)
> {
> return 0;
> }
> diff --git a/include/linux/dm-verity.h b/include/linux/dm-verity.h
> new file mode 100644
> index 000000000000..bb0413d55d72
> --- /dev/null
> +++ b/include/linux/dm-verity.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _LINUX_DM_VERITY_H
> +#define _LINUX_DM_VERITY_H
> +
> +#include <linux/types.h>
> +#include <crypto/hash_info.h>
> +#include <linux/device-mapper.h>
> +
> +struct dm_verity_digest {
> + const char *algo;
> + const u8 *digest;
> + size_t digest_len;
> +};
> +
> +#define DM_VERITY_SIGNATURE_SEC_NAME DM_NAME ".verity-signature"
> +#define DM_VERITY_ROOTHASH_SEC_NAME DM_NAME ".verity-roothash"
> +
> +#endif /* _LINUX_DM_VERITY_H */
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