Re: [PATCH RFC v11 14/19] ipe: add support for dm-verity as a trust provider

[Paul Moore <paul@paul-moore.com>]

On Oct  4, 2023 Fan Wu <wufan@linux.microsoft.com> wrote:
> 
> Allows author of IPE policy to indicate trust for a singular dm-verity
> volume, identified by roothash, through "dmverity_roothash" and all
> signed dm-verity volumes, through "dmverity_signature".
> 
> 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]
> 
> 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.
> 
> v9:
>   + Adapt to the new parser
> 
> v10:
>   + Select the Kconfig when all dependencies are enabled
> 
> v11:
>   + No changes
> ---
>  security/ipe/Kconfig         |  18 +++++
>  security/ipe/Makefile        |   1 +
>  security/ipe/audit.c         |  31 +++++++-
>  security/ipe/digest.c        | 142 +++++++++++++++++++++++++++++++++++
>  security/ipe/digest.h        |  26 +++++++
>  security/ipe/eval.c          | 101 ++++++++++++++++++++++++-
>  security/ipe/eval.h          |  13 ++++
>  security/ipe/hooks.c         |  51 +++++++++++++
>  security/ipe/hooks.h         |   8 ++
>  security/ipe/ipe.c           |  15 ++++
>  security/ipe/ipe.h           |   4 +
>  security/ipe/policy.h        |   3 +
>  security/ipe/policy_parser.c |  24 +++++-
>  13 files changed, 433 insertions(+), 4 deletions(-)
>  create mode 100644 security/ipe/digest.c
>  create mode 100644 security/ipe/digest.h

...

> diff --git a/security/ipe/audit.c b/security/ipe/audit.c
> index 0dd5f10c318f..b5c58655ac74 100644
> --- a/security/ipe/audit.c
> +++ b/security/ipe/audit.c
> @@ -13,6 +13,7 @@
>  #include "hooks.h"
>  #include "policy.h"
>  #include "audit.h"
> +#include "digest.h"
>  
>  #define ACTSTR(x) ((x) == IPE_ACTION_ALLOW ? "ALLOW" : "DENY")
>  
> @@ -40,8 +41,29 @@ static const char *const audit_op_names[__IPE_OP_MAX] = {
>  static const char *const audit_prop_names[__IPE_PROP_MAX] = {
>  	"boot_verified=FALSE",
>  	"boot_verified=TRUE",
> +#ifdef CONFIG_IPE_PROP_DM_VERITY
> +	"dmverity_roothash=",
> +	"dmverity_signature=FALSE",
> +	"dmverity_signature=TRUE",
> +#endif /* CONFIG_IPE_PROP_DM_VERITY */
>  };
>  
> +#ifdef CONFIG_IPE_PROP_DM_VERITY
> +/**
> + * audit_dmv_roothash - audit a roothash of a dmverity volume.
> + * @ab: Supplies a pointer to the audit_buffer to append to.
> + * @r: Supplies a pointer to the digest structure.
> + */
> +static void audit_dmv_roothash(struct audit_buffer *ab, const void *rh)
> +{
> +	ipe_digest_audit(ab, rh);
> +}
> +#else
> +static void audit_dmv_roothash(struct audit_buffer *ab, const void *rh)
> +{
> +}
> +#endif /* CONFIG_IPE_PROP_DM_VERITY */

Since the "dmverity_roothash=" field name is going to be written to
the audit record regardless of CONFIG_IPE_PROP_DM_VERITY we should
ensure that it has a value of "?" instead of nothing.  To fix that
I would suggest something like this:

  #else
  static void audit_dmv_roothash(struct audit_buffer *ab, const void *rh)
  {
    audit_log_format(ab, "?");
  }
  #endif /* CONFIG_IPE_PROP_DM_VERITY */

>  /**
>   * audit_rule - audit an IPE policy rule approximation.
>   * @ab: Supplies a pointer to the audit_buffer to append to.
> @@ -53,8 +75,13 @@ static void audit_rule(struct audit_buffer *ab, const struct ipe_rule *r)
>  
>  	audit_log_format(ab, "rule=\"op=%s ", audit_op_names[r->op]);
>  
> -	list_for_each_entry(ptr, &r->props, next)
> -		audit_log_format(ab, "%s ", audit_prop_names[ptr->type]);
> +	list_for_each_entry(ptr, &r->props, next) {
> +		audit_log_format(ab, "%s", audit_prop_names[ptr->type]);
> +		if (ptr->type == IPE_PROP_DMV_ROOTHASH)
> +			audit_dmv_roothash(ab, ptr->value);

If you wanted to avoid the roothash change above, you could change the
code here so it didn't always write "dmverity_roothash=" into the audit
record.

> +		audit_log_format(ab, " ");
> +	}
>  
>  	audit_log_format(ab, "action=%s\"", ACTSTR(r->action));
>  }
> diff --git a/security/ipe/digest.c b/security/ipe/digest.c
> new file mode 100644
> index 000000000000..7a42ca71880c
> --- /dev/null
> +++ b/security/ipe/digest.c
> @@ -0,0 +1,142 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) Microsoft Corporation. All rights reserved.
> + */
> +
> +#include "digest.h"
> +
> +/**
> + * ipe_digest_parse - parse a digest in IPE's policy.
> + * @valstr: Supplies the string parsed from the policy.
> + * @value: Supplies a pointer to be populated with the result.
> + *
> + * Digests in IPE are defined in a standard way:
> + *	<alg_name>:<hex>
> + *
> + * Use this function to create a property to parse the digest
> + * consistently. The parsed digest will be saved in @value in IPE's
> + * policy.
> + *
> + * Return:
> + * * 0	- OK
> + * * !0	- Error
> + */
> +int ipe_digest_parse(const char *valstr, void **value)

Why is @value void?  You should make it a digest_info type or simply
skip the second parameter and return a digest_info pointer.

> +{
> +	char *sep, *raw_digest;
> +	size_t raw_digest_len;
> +	int rc = 0;
> +	u8 *digest = NULL;
> +	struct digest_info *info = NULL;
> +
> +	info = kzalloc(sizeof(*info), GFP_KERNEL);
> +	if (!info)
> +		return -ENOMEM;
> +
> +	sep = strchr(valstr, ':');
> +	if (!sep) {
> +		rc = -EBADMSG;
> +		goto err;
> +	}
> +
> +	info->alg = kstrndup(valstr, sep - valstr, GFP_KERNEL);
> +	if (!info->alg) {
> +		rc = -ENOMEM;
> +		goto err;
> +	}
> +
> +	raw_digest = sep + 1;
> +	raw_digest_len = strlen(raw_digest);
> +	info->raw_digest = kstrndup(raw_digest, raw_digest_len, GFP_KERNEL);

Since you're running a strlen() over @raw_digest, you might as well
just use kstrdup() instead of kstrndup().

> +	if (!info->raw_digest) {
> +		rc = -ENOMEM;
> +		goto err_free_alg;
> +	}
> +
> +	info->digest_len = (raw_digest_len + 1) / 2;
> +	digest = kzalloc(info->digest_len, GFP_KERNEL);
> +	if (!digest) {
> +		rc = -ENOMEM;
> +		goto err_free_raw;
> +	}
> +
> +	rc = hex2bin(digest, raw_digest, info->digest_len);
> +	if (rc < 0) {
> +		rc = -EINVAL;
> +		goto err_free_raw;
> +	}
> +
> +	info->digest = digest;
> +	*value = info;
> +	return 0;
> +
> +err_free_raw:
> +	kfree(info->raw_digest);
> +err_free_alg:
> +	kfree(info->alg);
> +err:
> +	kfree(digest);
> +	kfree(info);
> +	return rc;
> +}
> +
> +/**
> + * ipe_digest_eval - evaluate an IPE digest against another digest.
> + * @expect: Supplies the policy-provided digest value.
> + * @digest: Supplies the digest to compare against the policy digest value.
> + * @digest_len: The length of @digest.
> + * @alg: Supplies the name of the algorithm used to calculated @digest.
> + *
> + * Return:
> + * * true	- digests match
> + * * false	- digests do not match
> + */
> +bool ipe_digest_eval(const void *expect, const u8 *digest, size_t digest_len,
> +		     const char *alg)

Similar to the above, why not make the @expect parameter a digest_info
type?  Also, why not pass a second digest_info parameter instead of
a separate @digest, @digest_len, and @alg?

> +{
> +	const struct digest_info *info = (struct digest_info *)expect;
> +
> +	return (digest_len == info->digest_len) && !strcmp(alg, info->alg) &&
> +	       (!memcmp(info->digest, digest, info->digest_len));
> +}
> +
> +/**
> + * ipe_digest_free - free an IPE digest.
> + * @value: Supplies a pointer the policy-provided digest value to free.
> + */
> +void ipe_digest_free(void **value)

Another digest_info parameter/type issue.

> +{
> +	struct digest_info *info = (struct digest_info *)(*value);
> +
> +	if (IS_ERR_OR_NULL(info))
> +		return;
> +
> +	kfree(info->alg);
> +	kfree(info->raw_digest);
> +	kfree(info->digest);
> +	kfree(info);
> +}
> +
> +/**
> + * ipe_digest_audit - audit a digest that was sourced from IPE's policy.
> + * @ab: Supplies the audit_buffer to append the formatted result.
> + * @val: Supplies a pointer to source the audit record from.
> + *
> + * Digests in IPE are defined in a standard way:
> + *	<alg_name>:<hex>
> + *
> + * Use this function to create a property to audit the digest
> + * consistently.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +void ipe_digest_audit(struct audit_buffer *ab, const void *val)

Another digest_info parameter/type issue.

> +{
> +	const struct digest_info *info = (struct digest_info *)val;
> +
> +	audit_log_untrustedstring(ab, info->alg);
> +	audit_log_format(ab, ":");
> +	audit_log_untrustedstring(ab, info->raw_digest);
> +}

...

> diff --git a/security/ipe/eval.c b/security/ipe/eval.c
> index 78c54ff1fdd3..82ad48d7aa3d 100644
> --- a/security/ipe/eval.c
> +++ b/security/ipe/eval.c
> @@ -69,15 +88,89 @@ void build_eval_ctx(struct ipe_eval_ctx *ctx,
>  		    const struct file *file,
>  		    enum ipe_op_type op)
>  {
> +	struct inode *ino = NULL;
> +
>  	if (op == IPE_OP_EXEC && file)
>  		pin_sb(FILE_SUPERBLOCK(file));
>  
>  	ctx->file = file;
>  	ctx->op = op;
>  
> -	if (file)
> +	if (file) {
>  		ctx->from_init_sb = from_pinned(FILE_SUPERBLOCK(file));
> +		ino = d_real_inode(file->f_path.dentry);
> +		build_ipe_bdev_ctx(ctx, ino);

You don't need @ino.

  build_ipe_bdev_ctx(ctx, d_real_inode(file->f_path.dentry));

> +	}
> +}
> +
> +#ifdef CONFIG_IPE_PROP_DM_VERITY
> +/**
> + * evaluate_dmv_roothash - Evaluate @ctx against a dmv roothash property.
> + * @ctx: Supplies a pointer to the context being evaluated.
> + * @p: Supplies a pointer to the property being evaluated.
> + *
> + * Return:
> + * * true	- The current @ctx match the @p
> + * * false	- The current @ctx doesn't match the @p
> + */
> +static bool evaluate_dmv_roothash(const struct ipe_eval_ctx *const ctx,
> +				  struct ipe_prop *p)
> +{
> +	return !!ctx->ipe_bdev &&
> +	       ipe_digest_eval(p->value,
> +			       ctx->ipe_bdev->digest,
> +			       ctx->ipe_bdev->digest_len,
> +			       ctx->ipe_bdev->digest_algo);

Building on my comments above in ipe_digest_eval(), if you convert it
to use digest_info structs this is simplified:

  ipe_digest_eval(p->vlaue, ctx->ipe_bdev)

> +}
> +
> +/**
> + * evaluate_dmv_sig_false: Analyze @ctx against a dmv sig false property.
> + * @ctx: Supplies a pointer to the context being evaluated.
> + * @p: Supplies a pointer to the property being evaluated.
> + *
> + * Return:
> + * * true	- The current @ctx match the @p
> + * * false	- The current @ctx doesn't match the @p
> + */
> +static bool evaluate_dmv_sig_false(const struct ipe_eval_ctx *const ctx,
> +				   struct ipe_prop *p)
> +{
> +	return !ctx->ipe_bdev || (!ctx->ipe_bdev->dm_verity_signed);
> +}
> +
> +/**
> + * evaluate_dmv_sig_true: Analyze @ctx against a dmv sig true property.
> + * @ctx: Supplies a pointer to the context being evaluated.
> + * @p: Supplies a pointer to the property being evaluated.
> + *
> + * Return:
> + * * true	- The current @ctx match the @p
> + * * false	- The current @ctx doesn't match the @p
> + */
> +static bool evaluate_dmv_sig_true(const struct ipe_eval_ctx *const ctx,
> +				  struct ipe_prop *p)
> +{
> +	return ctx->ipe_bdev && (!!ctx->ipe_bdev->dm_verity_signed);
> +}

Do you need both evaluate_dmv_sig_true() and evaluate_dmv_sig_false()?
If yes, you should make one call the other and return the inverse to
help ensure there are no oddities.

> diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
> index e9386762a597..8b8031e66f36 100644
> --- a/security/ipe/hooks.c
> +++ b/security/ipe/hooks.c
> @@ -193,3 +196,51 @@ void ipe_sb_free_security(struct super_block *mnt_sb)
>  {
>  	ipe_invalidate_pinned_sb(mnt_sb);
>  }
> +
> +#ifdef CONFIG_IPE_PROP_DM_VERITY
> +/**
> + * ipe_bdev_free_security - free IPE's LSM blob of block_devices.
> + * @bdev: Supplies a pointer to a block_device that contains the structure
> + *	  to free.
> + */
> +void ipe_bdev_free_security(struct block_device *bdev)
> +{
> +	struct ipe_bdev *blob = ipe_bdev(bdev);
> +
> +	kfree(blob->digest);
> +	kfree(blob->digest_algo);
> +}
> +
> +/**
> + * ipe_bdev_setsecurity - save data from a bdev to IPE's LSM blob.
> + * @bdev: Supplies a pointer to a block_device that contains the LSM blob.
> + * @key: Supplies the string key that uniquely identifies the value.
> + * @value: Supplies the value to store.
> + * @len: The length of @value.
> + */
> +int ipe_bdev_setsecurity(struct block_device *bdev, const char *key,
> +			 const void *value, size_t len)
> +{
> +	struct ipe_bdev *blob = ipe_bdev(bdev);
> +
> +	if (!strcmp(key, DM_VERITY_ROOTHASH_SEC_NAME)) {
> +		const struct dm_verity_digest *digest = value;
> +
> +		blob->digest = kmemdup(digest->digest, digest->digest_len, GFP_KERNEL);
> +		if (!blob->digest)
> +			return -ENOMEM;
> +
> +		blob->digest_algo = kstrdup_const(digest->algo, GFP_KERNEL);
> +		if (!blob->digest_algo)
> +			return -ENOMEM;

You need to cleanup @blob on error so you don't leak ipe_bdev::digest.

> +		blob->digest_len = digest->digest_len;
> +		return 0;
> +	} else if (!strcmp(key, DM_VERITY_SIGNATURE_SEC_NAME)) {
> +		blob->dm_verity_signed = true;
> +		return 0;
> +	}
> +
> +	return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_IPE_PROP_DM_VERITY */

--
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