linux-kernel - Re: [PATCH RFC v15 12/21] security: add security_bdev

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Message-ID: <f5cf9d285bd5f09bbc3f79b0800d37fc@paul-moore.com>
Date: Tue, 19 Mar 2024 19:00:36 -0400
From: Paul Moore <paul@...l-moore.com>
To: Fan Wu <wufan@...ux.microsoft.com>, corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org, serge@...lyn.com, tytso@....edu, ebiggers@...nel.org, axboe@...nel.dk, agk@...hat.com, snitzer@...nel.org, eparis@...hat.com
Cc: linux-doc@...r.kernel.org, linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, fsverity@...ts.linux.dev, linux-block@...r.kernel.org, dm-devel@...ts.linux.dev, audit@...r.kernel.org, linux-kernel@...r.kernel.org, Fan Wu <wufan@...ux.microsoft.com>
Subject: Re: [PATCH RFC v15 12/21] security: add security_bdev_setintegrity()  hook

On Mar 15, 2024 Fan Wu <wufan@...ux.microsoft.com> wrote:
> 
> This patch introduces a new hook to save block device's integrity
> data. For example, for dm-verity, LSMs can use this hook to save
> the roothash signature of a dm-verity into the security blob,
> and LSMs can make access decisions based on the data inside
> the signature, like the signer certificate.
> 
> Signed-off-by: Fan Wu <wufan@...ux.microsoft.com>
> 
> --
> v1-v14:
>   + Not present
> 
> v15:
>   + Introduced
> 
> ---
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/security.h      | 14 ++++++++++++++
>  security/security.c           | 28 ++++++++++++++++++++++++++++
>  3 files changed, 44 insertions(+)

I'm not sure why you made this a separate patch, help?  If there is
no significant reason why this is separate, please squash it together
with patch 11/21.

> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index c335404470dc..6808ae763913 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -455,4 +455,6 @@ LSM_HOOK(void, LSM_RET_VOID, initramfs_populated, void)
>  
>  LSM_HOOK(int, 0, bdev_alloc_security, struct block_device *bdev)
>  LSM_HOOK(void, LSM_RET_VOID, bdev_free_security, struct block_device *bdev)
> +LSM_HOOK(int, 0, bdev_setintegrity, struct block_device *bdev,
> +	 enum lsm_intgr_type type, const void *value, size_t size)
>  
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 9965b5c50df4..eaff8868766a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -83,6 +83,10 @@ enum lsm_event {
>  	LSM_POLICY_CHANGE,
>  };
>  
> +enum lsm_intgr_type {
> +	__LSM_INTGR_MAX
> +};
> +
>  /*
>   * These are reasons that can be passed to the security_locked_down()
>   * LSM hook. Lockdown reasons that protect kernel integrity (ie, the
> @@ -511,6 +515,9 @@ int lsm_fill_user_ctx(struct lsm_ctx __user *uctx, u32 *uctx_len,
>  		      void *val, size_t val_len, u64 id, u64 flags);
>  int security_bdev_alloc(struct block_device *bdev);
>  void security_bdev_free(struct block_device *bdev);
> +int security_bdev_setintegrity(struct block_device *bdev,
> +			       enum lsm_intgr_type type, const void *value,
> +			       size_t size);
>  #else /* CONFIG_SECURITY */
>  
>  static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
> @@ -1495,6 +1502,13 @@ static inline void security_bdev_free(struct block_device *bdev)
>  {
>  }
>  
> +static inline int security_bdev_setintegrity(struct block_device *bdev,
> +					     enum lsm_intgr_type, type,
> +					     const void *value, size_t size)
> +{
> +	return 0;
> +}
> +
>  #endif	/* CONFIG_SECURITY */
>  
>  #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
> diff --git a/security/security.c b/security/security.c
> index 4274bbee40d0..8d88529ac904 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5637,6 +5637,34 @@ void security_bdev_free(struct block_device *bdev)
>  }
>  EXPORT_SYMBOL(security_bdev_free);
>  
> +/**
> + * security_bdev_setintegrity() - Set the bdev's integrity data

Let's just say "Set the device's integrity data" and not ask people to
figure out "bdev", although I will admit it should be fairly obvious :)

> + * @bdev: block device
> + * @type: type of integrity, e.g. hash digest, signature, etc
> + * @value: the integrity value
> + * @size: size of the integrity value
> + *
> + * Register a verified integrity measurement of a bdev with the LSM.
> + *
> + * Return: Returns 0 on success, negative values on failure.
> + */
> +int security_bdev_setintegrity(struct block_device *bdev,
> +			       enum lsm_intgr_type type, const void *value,
> +			       size_t size)
> +{
> +	int rc = 0;
> +	struct security_hook_list *p;
> +
> +	hlist_for_each_entry(p, &security_hook_heads.bdev_setintegrity, list) {
> +		rc = p->hook.bdev_setintegrity(bdev, type, value, size);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return LSM_RET_DEFAULT(bdev_setintegrity);

We can just use the call_int_hook() macro here instead of open coding
everything, right?

> +}
> +EXPORT_SYMBOL(security_bdev_setintegrity);
> +
>  #ifdef CONFIG_PERF_EVENTS
>  /**
>   * security_perf_event_open() - Check if a perf event open is allowed
> -- 
> 2.44.0

--
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