Re: [PATCH RFC v11 13/19] dm verity: consume root hash digest and signature data via LSM hook

Paul Moore
2023-11-02T00:42:06Z

On Mon, Oct 23, 2023 at 11:52 PM Paul Moore <paul@paul-moore.com> wrote:
>
> On Oct 4, 2023 Fan Wu <wufan@linux.microsoft.com> wrote:
> >
> > 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 added two security hook calls in dm-verity to save the
> > dm-verity roothash and the roothash signature to the block device's
> > LSM blobs.
> >
> > 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
> >
> > v10:
> > + No changes
> >
> > v11:
> > + Add an optional field to save signature
> > + Move the security hook call to the new finalize hook
> > ---
> > drivers/md/dm-verity-target.c | 71 +++++++++++++++++++++++++++++++++++
> > drivers/md/dm-verity.h | 6 +++
> > include/linux/dm-verity.h | 19 ++++++++++
> > 3 files changed, 96 insertions(+)
> > create mode 100644 include/linux/dm-verity.h
>
> We need an ACK from Alasdair and/or Mike on this too.

A gentle ping with a reminder ...

For reference, the full patchset can be found on lore at the link below:

https://lore.kernel.org/linux-security-module/1696457386-3010-1-git-send-email-wufan@linux.microsoft.com/

> > diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> > index 80673b66c194..db58b53649e3 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"
> > @@ -22,6 +23,9 @@
> > #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"
> >
> > @@ -952,6 +956,17 @@ static void verity_io_hints(struct dm_target *ti, struct queue_limits *limits)
> > blk_limits_io_min(limits, limits->logical_block_size);
> > }
> >
> > +#ifdef CONFIG_IPE_PROP_DM_VERITY
> > +static void verity_free_sig(struct dm_verity *v)
> > +{
> > + kfree(v->root_digest_sig);
> > +}
> > +#else
> > +static inline void verity_free_sig(struct dm_verity *v)
> > +{
> > +}
> > +#endif /* CONFIG_IPE_PROP_DM_VERITY */
> > +
> > static void verity_dtr(struct dm_target *ti)
> > {
> > struct dm_verity *v = ti->private;
> > @@ -966,6 +981,7 @@ 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);
> > @@ -1157,6 +1173,25 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
> > return r;
> > }
> >
> > +#ifdef CONFIG_IPE_PROP_DM_VERITY
> > +static int verity_init_sig(struct dm_verity *v, const void *sig,
> > + size_t sig_size)
> > +{
> > + v->sig_size = sig_size;
> > + v->root_digest_sig = kmalloc(v->sig_size, GFP_KERNEL);
> > + if (!v->root_digest)
> > + return -ENOMEM;
> > +
> > + return 0;
> > +}
> > +#else
> > +static inline int verity_init_sig(struct dm_verity *v, const void *sig,
> > + size_t sig_size)
> > +{
> > + return 0;
> > +}
> > +#endif /* CONFIG_IPE_PROP_DM_VERITY */
> > +
> > /*
> > * Target parameters:
> > * <version> The current format is version 1.
> > @@ -1365,6 +1400,13 @@ 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);
> >
> > @@ -1501,6 +1543,32 @@ int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest, unsigned i
> > return 0;
> > }
> >
> > +#ifdef CONFIG_IPE_PROP_DM_VERITY
> > +static int verity_finalize(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_table_get_md(ti->table)->disk->part0;
> > + 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)
> > + return r;
> > +
> > + return security_bdev_setsecurity(bdev,
> > + DM_VERITY_SIGNATURE_SEC_NAME,
> > + v->root_digest_sig,
> > + v->sig_size);
> > +}
> > +#endif /* CONFIG_IPE_PROP_DM_VERITY */
> > +
> > static struct target_type verity_target = {
> > .name = "verity",
> > .features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE,
> > @@ -1513,6 +1581,9 @@ static struct target_type verity_target = {
> > .prepare_ioctl = verity_prepare_ioctl,
> > .iterate_devices = verity_iterate_devices,
> > .io_hints = verity_io_hints,
> > +#ifdef CONFIG_IPE_PROP_DM_VERITY
> > + .finalize = verity_finalize,
> > +#endif /* CONFIG_IPE_PROP_DM_VERITY */
> > };
> > module_dm(verity);
> >
> > diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
> > index 2f555b420367..a093d4a54615 100644
> > --- a/drivers/md/dm-verity.h
> > +++ b/drivers/md/dm-verity.h
> > @@ -42,6 +42,9 @@ 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_IPE_PROP_DM_VERITY
> > + u8 *root_digest_sig; /* digest signature of the root block */
> > +#endif /* CONFIG_IPE_PROP_DM_VERITY */
> > unsigned int salt_size;
> > sector_t data_start; /* data offset in 512-byte sectors */
> > sector_t hash_start; /* hash start in blocks */
> > @@ -55,6 +58,9 @@ struct dm_verity {
> > bool hash_failed:1; /* set if hash of any block failed */
> > bool use_tasklet:1; /* try to verify in tasklet before work-queue */
> > unsigned int digest_size; /* digest size for the current hash algorithm */
> > +#ifdef CONFIG_IPE_PROP_DM_VERITY
> > + unsigned int sig_size; /* digest signature size */
> > +#endif /* CONFIG_IPE_PROP_DM_VERITY */
> > 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/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 */
> > --
> > 2.25.1

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