[PATCH v19 12/20] dm verity: expose root hash digest and signature data to LSMs
Mikulas Patocka
mpatocka at redhat.com
Sat May 25 09:02:39 UTC 2024
Reviewed-by: Mikulas Patocka <mpatocka at redhat.com>
On Fri, 24 May 2024, 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.
>
> 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.
>
> This patch adds two security hook calls in dm-verity to expose the
> dm-verity roothash and the roothash signature to LSMs via preresume
> callback. The hook calls are depended on CONFIG_SECURITY.
>
> 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
>
> v10:
> + No changes
>
> v11:
> + Add an optional field to save signature
> + Move the security hook call to the new finalize hook
>
> v12:
> + No changes
>
> v13:
> + No changes
>
> v14:
> + Correct code format
> + Remove unnecessary header and switch to dm_disk()
>
> v15:
> + Refactor security_bdev_setsecurity() to security_bdev_setintegrity()
> + Remove unnecessary headers
>
> v16:
> + Use kmemdup to duplicate signature
> + Clean up lsm blob data in error case
>
> v17:
> + Switch to depend on CONFIG_SECURITY
> + Use new enum name LSM_INT_DMVERITY_SIG_VALID
>
> v18:
> + Amend commit title
> + Fix incorrect error handling
> + Make signature exposure depends on CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
> + Fix inaccurate comment
> + Remove include/linux/dm-verity.h
> + use crypto_ahash_alg_name(v->tfm) instead of v->alg_name
>
> v19:
> + Drop finalize callback and switch to preresume callback
> + Adding NULL check to avoid kmemdup when sig is NULL
> ---
> drivers/md/dm-verity-target.c | 108 ++++++++++++++++++++++++++++++++++
> drivers/md/dm-verity.h | 6 ++
> include/linux/security.h | 9 ++-
> 3 files changed, 122 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index bb5da66da4c1..0a54ce02ea53 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -22,6 +22,7 @@
> #include <linux/scatterlist.h>
> #include <linux/string.h>
> #include <linux/jump_label.h>
> +#include <linux/security.h>
>
> #define DM_MSG_PREFIX "verity"
>
> @@ -1017,6 +1018,41 @@ static void verity_io_hints(struct dm_target *ti, struct queue_limits *limits)
> blk_limits_io_min(limits, limits->logical_block_size);
> }
>
> +#ifdef CONFIG_SECURITY
> +
> +static int verity_init_sig(struct dm_verity *v, const void *sig,
> + size_t sig_size)
> +{
> + v->sig_size = sig_size;
> +
> + if (sig) {
> + v->root_digest_sig = kmemdup(sig, v->sig_size, GFP_KERNEL);
> + if (!v->root_digest_sig)
> + return -ENOMEM;
> + }
> +
> + return 0;
> +}
> +
> +static void verity_free_sig(struct dm_verity *v)
> +{
> + kfree(v->root_digest_sig);
> +}
> +
> +#else
> +
> +static inline int verity_init_sig(struct dm_verity *v, const void *sig,
> + size_t sig_size)
> +{
> + return 0;
> +}
> +
> +static inline void verity_free_sig(struct dm_verity *v)
> +{
> +}
> +
> +#endif /* CONFIG_SECURITY */
> +
> static void verity_dtr(struct dm_target *ti)
> {
> struct dm_verity *v = ti->private;
> @@ -1035,6 +1071,7 @@ static void verity_dtr(struct dm_target *ti)
> kfree(v->salt);
> kfree(v->root_digest);
> kfree(v->zero_digest);
> + verity_free_sig(v);
>
> if (v->tfm)
> crypto_free_ahash(v->tfm);
> @@ -1434,6 +1471,13 @@ static int verity_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> ti->error = "Root hash verification failed";
> goto bad;
> }
> +
> + r = verity_init_sig(v, verify_args.sig, verify_args.sig_size);
> + if (r < 0) {
> + ti->error = "Cannot allocate root digest signature";
> + goto bad;
> + }
> +
> v->hash_per_block_bits =
> __fls((1 << v->hash_dev_block_bits) / v->digest_size);
>
> @@ -1584,6 +1628,67 @@ int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest, unsigned i
> return 0;
> }
>
> +#ifdef CONFIG_SECURITY
> +
> +#ifdef CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
> +
> +static int verity_security_set_signature(struct block_device *bdev,
> + struct dm_verity *v)
> +{
> + return security_bdev_setintegrity(bdev,
> + LSM_INT_DMVERITY_SIG_VALID,
> + v->root_digest_sig,
> + v->sig_size);
> +}
> +
> +#else
> +
> +static inline int verity_security_set_signature(struct block_device *bdev,
> + struct dm_verity *v)
> +{
> + return 0;
> +}
> +
> +#endif /* CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG */
> +
> +/*
> + * Expose verity target's root hash and signature data to LSMs before resume.
> + *
> + * Returns 0 on success, or -ENOMEM if the system is out of memory.
> + */
> +static int verity_preresume(struct dm_target *ti)
> +{
> + struct block_device *bdev;
> + struct dm_verity_digest root_digest;
> + struct dm_verity *v;
> + int r;
> +
> + v = ti->private;
> + bdev = dm_disk(dm_table_get_md(ti->table))->part0;
> + root_digest.digest = v->root_digest;
> + root_digest.digest_len = v->digest_size;
> + root_digest.alg = crypto_ahash_alg_name(v->tfm);
> +
> + r = security_bdev_setintegrity(bdev, LSM_INT_DMVERITY_ROOTHASH, &root_digest,
> + sizeof(root_digest));
> + if (r)
> + return r;
> +
> + r = verity_security_set_signature(bdev, v);
> + if (r)
> + goto bad;
> +
> + return 0;
> +
> +bad:
> +
> + security_bdev_setintegrity(bdev, LSM_INT_DMVERITY_ROOTHASH, NULL, 0);
> +
> + return r;
> +}
> +
> +#endif /* CONFIG_SECURITY */
> +
> static struct target_type verity_target = {
> .name = "verity",
> .features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE,
> @@ -1596,6 +1701,9 @@ static struct target_type verity_target = {
> .prepare_ioctl = verity_prepare_ioctl,
> .iterate_devices = verity_iterate_devices,
> .io_hints = verity_io_hints,
> +#ifdef CONFIG_SECURITY
> + .preresume = verity_preresume,
> +#endif /* CONFIG_SECURITY */
> };
> module_dm(verity);
>
> diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
> index 20b1bcf03474..2de89e0d555b 100644
> --- a/drivers/md/dm-verity.h
> +++ b/drivers/md/dm-verity.h
> @@ -43,6 +43,9 @@ struct dm_verity {
> u8 *root_digest; /* digest of the root block */
> u8 *salt; /* salt: its size is salt_size */
> u8 *zero_digest; /* digest for a zero block */
> +#ifdef CONFIG_SECURITY
> + u8 *root_digest_sig; /* signature of the root digest */
> +#endif /* CONFIG_SECURITY */
> unsigned int salt_size;
> sector_t data_start; /* data offset in 512-byte sectors */
> sector_t hash_start; /* hash start in blocks */
> @@ -56,6 +59,9 @@ struct dm_verity {
> bool hash_failed:1; /* set if hash of any block failed */
> bool use_bh_wq:1; /* try to verify in BH wq before normal work-queue */
> unsigned int digest_size; /* digest size for the current hash algorithm */
> +#ifdef CONFIG_SECURITY
> + unsigned int sig_size; /* root digest signature size */
> +#endif /* CONFIG_SECURITY */
> unsigned int ahash_reqsize;/* the size of temporary space for crypto */
> enum verity_mode mode; /* mode for handling verification errors */
> unsigned int corrupted_errs;/* Number of errors for corrupted blocks */
> diff --git a/include/linux/security.h b/include/linux/security.h
> index a64e83622c7c..09c80326518f 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -83,8 +83,15 @@ enum lsm_event {
> LSM_POLICY_CHANGE,
> };
>
> +struct dm_verity_digest {
> + const char *alg;
> + const u8 *digest;
> + size_t digest_len;
> +};
> +
> enum lsm_integrity_type {
> - __LSM_INT_MAX
> + LSM_INT_DMVERITY_SIG_VALID,
> + LSM_INT_DMVERITY_ROOTHASH,
> };
>
> /*
> --
> 2.44.0
>
More information about the Linux-security-module-archive
mailing list