Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <14754d16-75ae-cc92-cfc5-adce0628d9d9@schaufler-ca.com>
Date:   Wed, 8 Jun 2022 13:07:39 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.10.0
Subject: Re: [RFC PATCH v8 10/17] block|security: add LSM blob to block_device
Content-Language: en-US
To:     Deven Bowers <deven.desai@linux.microsoft.com>, corbet@lwn.net,
        zohar@linux.ibm.com, jmorris@namei.org, serge@hallyn.com,
        tytso@mit.edu, ebiggers@kernel.org, axboe@kernel.dk,
        agk@redhat.com, snitzer@kernel.org, eparis@redhat.com,
        paul@paul-moore.com
Cc:     linux-doc@vger.kernel.org, linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-fscrypt@vger.kernel.org, linux-block@vger.kernel.org,
        dm-devel@redhat.com, linux-audit@redhat.com,
        roberto.sassu@huawei.com, linux-kernel@vger.kernel.org,
        Casey Schaufler <casey@schaufler-ca.com>
References: <1654714889-26728-1-git-send-email-deven.desai@linux.microsoft.com>
 <1654714889-26728-11-git-send-email-deven.desai@linux.microsoft.com>
From:   Casey Schaufler <casey@schaufler-ca.com>
In-Reply-To: <1654714889-26728-11-git-send-email-deven.desai@linux.microsoft.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 6/8/2022 12:01 PM, Deven Bowers wrote:
> block_device structures can have valuable security properties,
> based on how they are created, and what subsystem manages them.
>
> By adding LSM storage to this structure, this data can be accessed
> at the LSM layer.
>
> Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>

Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>

Not everyone is going to appreciate the infrastructure allocation
of the block_device security blob, but I do.

>
> ---
> v2:
>    + No Changes
>
> v3:
>    + Minor style changes from checkpatch --strict
>
> v4:
>    + No Changes
>
> v5:
>    + Allow multiple callers to call security_bdev_setsecurity
>
> v6:
>    + Simplify security_bdev_setsecurity break condition
>
> v7:
>    + Squash all dm-verity related patches to two patches,
>      the additions to dm-verity/fs, and the consumption of
>      the additions.
>
> v8:
>    + Split dm-verity related patches squashed in v7 to 3 commits based on
>      topic:
>        + New LSM hook
>        + Consumption of hook outside LSM
>        + Consumption of hook inside LSM.
>
>    + change return of security_bdev_alloc / security_bdev_setsecurity
>      to LSM_RET_DEFAULT instead of 0.
>
>    + Change return code to -EOPNOTSUPP, bring inline with other
>      setsecurity hooks.
> ---
>   block/bdev.c                  |  7 ++++
>   include/linux/blk_types.h     |  1 +
>   include/linux/lsm_hook_defs.h |  5 +++
>   include/linux/lsm_hooks.h     | 12 ++++++
>   include/linux/security.h      | 22 +++++++++++
>   security/security.c           | 70 +++++++++++++++++++++++++++++++++++
>   6 files changed, 117 insertions(+)
>
> diff --git a/block/bdev.c b/block/bdev.c
> index 5fe06c1f2def..e7ef2c7a22c9 100644
> --- a/block/bdev.c
> +++ b/block/bdev.c
> @@ -24,6 +24,7 @@
>   #include <linux/pseudo_fs.h>
>   #include <linux/uio.h>
>   #include <linux/namei.h>
> +#include <linux/security.h>
>   #include <linux/part_stat.h>
>   #include <linux/uaccess.h>
>   #include "../fs/internal.h"
> @@ -397,6 +398,11 @@ static struct inode *bdev_alloc_inode(struct super_block *sb)
>   	if (!ei)
>   		return NULL;
>   	memset(&ei->bdev, 0, sizeof(ei->bdev));
> +
> +	if (unlikely(security_bdev_alloc(&ei->bdev))) {
> +		kmem_cache_free(bdev_cachep, ei);
> +		return NULL;
> +	}
>   	return &ei->vfs_inode;
>   }
>   
> @@ -406,6 +412,7 @@ static void bdev_free_inode(struct inode *inode)
>   
>   	free_percpu(bdev->bd_stats);
>   	kfree(bdev->bd_meta_info);
> +	security_bdev_free(bdev);
>   
>   	if (!bdev_is_partition(bdev)) {
>   		if (bdev->bd_disk && bdev->bd_disk->bdi)
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index a24d4078fb21..a014ffa14b2d 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -68,6 +68,7 @@ struct block_device {
>   #ifdef CONFIG_FAIL_MAKE_REQUEST
>   	bool			bd_make_it_fail;
>   #endif
> +	void			*security;
>   } __randomize_layout;
>   
>   #define bdev_whole(_bdev) \
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index eafa1d2489fd..3449c004bd84 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -407,3 +407,8 @@ LSM_HOOK(int, 0, perf_event_write, struct perf_event *event)
>   LSM_HOOK(int, 0, uring_override_creds, const struct cred *new)
>   LSM_HOOK(int, 0, uring_sqpoll, void)
>   #endif /* CONFIG_IO_URING */
> +
> +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_setsecurity, struct block_device *bdev, const char *name,
> +	 const void *value, size_t size)
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 91c8146649f5..9f011d705ea8 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1550,6 +1550,17 @@
>    *
>    *     @what: kernel feature being accessed
>    *
> + * @bdev_alloc_security:
> + *	Initialize the security field inside a block_device structure.
> + *
> + * @bdev_free_security:
> + *	Cleanup the security information stored inside a block_device structure.
> + *
> + * @bdev_setsecurity:
> + *	Set a security property associated with @name for @bdev with
> + *	value @value. @size indicates the size of @value in bytes.
> + *	If a @name is not implemented, return -EOPNOTSUPP.
> + *
>    * Security hooks for perf events
>    *
>    * @perf_event_open:
> @@ -1610,6 +1621,7 @@ struct lsm_blob_sizes {
>   	int	lbs_ipc;
>   	int	lbs_msg_msg;
>   	int	lbs_task;
> +	int	lbs_bdev;
>   };
>   
>   /*
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 7fc4e9f49f54..30b663de301f 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -473,6 +473,11 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
>   int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
>   int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
>   int security_locked_down(enum lockdown_reason what);
> +int security_bdev_alloc(struct block_device *bdev);
> +void security_bdev_free(struct block_device *bdev);
> +int security_bdev_setsecurity(struct block_device *bdev,
> +			      const char *name, const void *value,
> +			      size_t size);
>   #else /* CONFIG_SECURITY */
>   
>   static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
> @@ -1349,6 +1354,23 @@ static inline int security_locked_down(enum lockdown_reason what)
>   {
>   	return 0;
>   }
> +
> +static inline int security_bdev_alloc(struct block_device *bdev)
> +{
> +	return 0;
> +}
> +
> +static inline void security_bdev_free(struct block_device *bdev)
> +{
> +}
> +
> +static inline int security_bdev_setsecurity(struct block_device *bdev,
> +					    const char *name,
> +					    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 188b8f782220..59ec336788e8 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -29,6 +29,7 @@
>   #include <linux/string.h>
>   #include <linux/msg.h>
>   #include <net/flow.h>
> +#include <linux/fs.h>
>   
>   #define MAX_LSM_EVM_XATTR	2
>   
> @@ -208,6 +209,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
>   	lsm_set_blob_size(&needed->lbs_msg_msg, &blob_sizes.lbs_msg_msg);
>   	lsm_set_blob_size(&needed->lbs_superblock, &blob_sizes.lbs_superblock);
>   	lsm_set_blob_size(&needed->lbs_task, &blob_sizes.lbs_task);
> +	lsm_set_blob_size(&needed->lbs_bdev, &blob_sizes.lbs_bdev);
>   }
>   
>   /* Prepare LSM for initialization. */
> @@ -344,6 +346,7 @@ static void __init ordered_lsm_init(void)
>   	init_debug("msg_msg blob size    = %d\n", blob_sizes.lbs_msg_msg);
>   	init_debug("superblock blob size = %d\n", blob_sizes.lbs_superblock);
>   	init_debug("task blob size       = %d\n", blob_sizes.lbs_task);
> +	init_debug("bdev blob size       = %d\n", blob_sizes.lbs_bdev);
>   
>   	/*
>   	 * Create any kmem_caches needed for blobs
> @@ -660,6 +663,28 @@ static int lsm_msg_msg_alloc(struct msg_msg *mp)
>   	return 0;
>   }
>   
> +/**
> + * lsm_bdev_alloc - allocate a composite block_device blob
> + * @bdev: the block_device that needs a blob
> + *
> + * Allocate the block_device blob for all the modules
> + *
> + * Returns 0, or -ENOMEM if memory can't be allocated.
> + */
> +static int lsm_bdev_alloc(struct block_device *bdev)
> +{
> +	if (blob_sizes.lbs_bdev == 0) {
> +		bdev->security = NULL;
> +		return 0;
> +	}
> +
> +	bdev->security = kzalloc(blob_sizes.lbs_bdev, GFP_KERNEL);
> +	if (!bdev->security)
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
>   /**
>    * lsm_early_task - during initialization allocate a composite task blob
>    * @task: the task that needs a blob
> @@ -2617,6 +2642,51 @@ int security_locked_down(enum lockdown_reason what)
>   }
>   EXPORT_SYMBOL(security_locked_down);
>   
> +int security_bdev_alloc(struct block_device *bdev)
> +{
> +	int rc = 0;
> +
> +	rc = lsm_bdev_alloc(bdev);
> +	if (unlikely(rc))
> +		return rc;
> +
> +	rc = call_int_hook(bdev_alloc_security, 0, bdev);
> +	if (unlikely(rc))
> +		security_bdev_free(bdev);
> +
> +	return LSM_RET_DEFAULT(bdev_alloc_security);
> +}
> +EXPORT_SYMBOL(security_bdev_alloc);
> +
> +void security_bdev_free(struct block_device *bdev)
> +{
> +	if (!bdev->security)
> +		return;
> +
> +	call_void_hook(bdev_free_security, bdev);
> +
> +	kfree(bdev->security);
> +	bdev->security = NULL;
> +}
> +EXPORT_SYMBOL(security_bdev_free);
> +
> +int security_bdev_setsecurity(struct block_device *bdev,
> +			      const char *name, const void *value,
> +			      size_t size)
> +{
> +	int rc = 0;
> +	struct security_hook_list *p;
> +
> +	hlist_for_each_entry(p, &security_hook_heads.bdev_setsecurity, list) {
> +		rc = p->hook.bdev_setsecurity(bdev, name, value, size);
> +		if (rc && rc != -EOPNOTSUPP)
> +			return rc;
> +	}
> +
> +	return LSM_RET_DEFAULT(bdev_setsecurity);
> +}
> +EXPORT_SYMBOL(security_bdev_setsecurity);
> +
>   #ifdef CONFIG_PERF_EVENTS
>   int security_perf_event_open(struct perf_event_attr *attr, int type)
>   {