Re: [RFC PATCH v9 10/16] dm-verity: consume root hash digest and signature data via LSM hook

[Roberto Sassu <roberto.sassu@huaweicloud.com>]

On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote:
> From: Deven Bowers <deven.desai@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@linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan@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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