Re: [RFC v1 05/14] krsi: Initialize KRSI hooks and create files in securityfs

[Yonghong Song <yhs@fb.com>]

On 9/10/19 12:55 PM, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
> 
> The LSM creates files in securityfs for each hook registered with the
> LSM.
> 
>      /sys/kernel/security/bpf/<h_name>
> 
> The initialization of the hooks is done collectively in an internal
> header "hooks.h" which results in:
> 
> * Creation of a file for the hook in the securityfs.
> * Allocation of a krsi_hook data structure which stores a pointer to the
>    dentry of the newly created file in securityfs.
> * A pointer to the krsi_hook data structure is stored in the private
>    d_fsdata of dentry of the file created in securityFS.
> 
> These files will later be used to specify an attachment target during
> BPF_PROG_LOAD.
> 
> Signed-off-by: KP Singh <kpsingh@google.com>
> ---
>   security/krsi/Makefile            |  4 +-
>   security/krsi/include/hooks.h     | 21 ++++++++
>   security/krsi/include/krsi_fs.h   | 19 +++++++
>   security/krsi/include/krsi_init.h | 45 ++++++++++++++++
>   security/krsi/krsi.c              | 16 +++++-
>   security/krsi/krsi_fs.c           | 88 +++++++++++++++++++++++++++++++
>   6 files changed, 191 insertions(+), 2 deletions(-)
>   create mode 100644 security/krsi/include/hooks.h
>   create mode 100644 security/krsi/include/krsi_fs.h
>   create mode 100644 security/krsi/include/krsi_init.h
>   create mode 100644 security/krsi/krsi_fs.c
> 
> diff --git a/security/krsi/Makefile b/security/krsi/Makefile
> index 660cc1f422fd..4586241f16e1 100644
> --- a/security/krsi/Makefile
> +++ b/security/krsi/Makefile
> @@ -1 +1,3 @@
> -obj-$(CONFIG_SECURITY_KRSI) := krsi.o ops.o
> +obj-$(CONFIG_SECURITY_KRSI) := krsi.o krsi_fs.o ops.o
> +
> +ccflags-y := -I$(srctree)/security/krsi -I$(srctree)/security/krsi/include
> diff --git a/security/krsi/include/hooks.h b/security/krsi/include/hooks.h
> new file mode 100644
> index 000000000000..e070c452b5de
> --- /dev/null
> +++ b/security/krsi/include/hooks.h
> @@ -0,0 +1,21 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * The hooks for the KRSI LSM are declared in this file.
> + *
> + * This header MUST NOT be included directly and should
> + * be only used to initialize the hooks lists.
> + *
> + * Format:
> + *
> + *   KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN)
> + *
> + * KRSI adds one layer of indirection between the name of the hook and the name
> + * it exposes to the userspace in Security FS to prevent the userspace from
> + * breaking in case the name of the hook changes in the kernel or if there's
> + * another LSM hook that maps better to the represented security behaviour.
> + */
> +KRSI_HOOK_INIT(PROCESS_EXECUTION,
> +	       process_execution,
> +	       bprm_check_security,
> +	       krsi_process_execution)
> diff --git a/security/krsi/include/krsi_fs.h b/security/krsi/include/krsi_fs.h
> new file mode 100644
> index 000000000000..38134661d8d6
> --- /dev/null
> +++ b/security/krsi/include/krsi_fs.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _KRSI_FS_H
> +#define _KRSI_FS_H
> +
> +#include <linux/bpf.h>
> +#include <linux/fs.h>
> +#include <linux/types.h>
> +
> +bool is_krsi_hook_file(struct file *f);
> +
> +/*
> + * The name of the directory created in securityfs
> + *
> + *	/sys/kernel/security/<dir_name>
> + */
> +#define KRSI_SFS_NAME "krsi"
> +
> +#endif /* _KRSI_FS_H */
> diff --git a/security/krsi/include/krsi_init.h b/security/krsi/include/krsi_init.h
> new file mode 100644
> index 000000000000..68755182a031
> --- /dev/null
> +++ b/security/krsi/include/krsi_init.h
> @@ -0,0 +1,45 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _KRSI_INIT_H
> +#define _KRSI_INIT_H
> +
> +#include "krsi_fs.h"
> +
> +enum krsi_hook_type {
> +	PROCESS_EXECUTION,
> +	__MAX_KRSI_HOOK_TYPE, /* delimiter */
> +};
> +
> +extern int krsi_fs_initialized;
> +/*
> + * The LSM creates one file per hook.
> + *
> + * A pointer to krsi_hook data structure is stored in the
> + * private fsdata of the dentry of the per-hook file created
> + * in securityfs.
> + */
> +struct krsi_hook {
> +	/*
> +	 * The name of the security hook, a file with this name will be created
> +	 * in the securityfs.
> +	 */
> +	const char *name;
> +	/*
> +	 * The type of the LSM hook, the LSM uses this to index the list of the
> +	 * hooks to run the eBPF programs that may have been attached.
> +	 */
> +	enum krsi_hook_type h_type;
> +	/*
> +	 * The dentry of the file created in securityfs.
> +	 */
> +	struct dentry *h_dentry;
> +};
> +
> +extern struct krsi_hook krsi_hooks_list[];
> +
> +#define krsi_for_each_hook(hook) \
> +	for ((hook) = &krsi_hooks_list[0]; \
> +	     (hook) < &krsi_hooks_list[__MAX_KRSI_HOOK_TYPE]; \
> +	     (hook)++)
> +
> +#endif /* _KRSI_INIT_H */
> diff --git a/security/krsi/krsi.c b/security/krsi/krsi.c
> index 9ce4f56fb78d..77d7e2f91172 100644
> --- a/security/krsi/krsi.c
> +++ b/security/krsi/krsi.c
> @@ -2,13 +2,27 @@
>   
>   #include <linux/lsm_hooks.h>
>   
> +#include "krsi_init.h"
> +
> +struct krsi_hook krsi_hooks_list[] = {
> +	#define KRSI_HOOK_INIT(TYPE, NAME, H, I) \
> +		[TYPE] = { \
> +			.h_type = TYPE, \
> +			.name = #NAME, \
> +		},
> +	#include "hooks.h"
> +	#undef KRSI_HOOK_INIT
> +};
> +
>   static int krsi_process_execution(struct linux_binprm *bprm)
>   {
>   	return 0;
>   }
>   
>   static struct security_hook_list krsi_hooks[] __lsm_ro_after_init = {
> -	LSM_HOOK_INIT(bprm_check_security, krsi_process_execution),
> +	#define KRSI_HOOK_INIT(T, N, HOOK, IMPL) LSM_HOOK_INIT(HOOK, IMPL),
> +	#include "hooks.h"
> +	#undef KRSI_HOOK_INIT
>   };
>   
>   static int __init krsi_init(void)
> diff --git a/security/krsi/krsi_fs.c b/security/krsi/krsi_fs.c
> new file mode 100644
> index 000000000000..604f826cee5c
> --- /dev/null
> +++ b/security/krsi/krsi_fs.c
> @@ -0,0 +1,88 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/err.h>
> +#include <linux/init.h>
> +#include <linux/file.h>
> +#include <linux/fs.h>
> +#include <linux/types.h>
> +#include <linux/security.h>
> +
> +#include "krsi_fs.h"
> +#include "krsi_init.h"
> +
> +extern struct krsi_hook krsi_hooks_list[];
> +
> +static struct dentry *krsi_dir;
> +
> +static const struct file_operations krsi_hook_ops = {
> +	.llseek = generic_file_llseek,
> +};
> +
> +int krsi_fs_initialized;
> +
> +bool is_krsi_hook_file(struct file *f)
> +{
> +	return f->f_op == &krsi_hook_ops;
> +}
> +
> +static void __init krsi_free_hook(struct krsi_hook *h)
> +{
> +	securityfs_remove(h->h_dentry);
> +	h->h_dentry = NULL;
> +}
> +
> +static int __init krsi_init_hook(struct krsi_hook *h, struct dentry *parent)
> +{
> +	struct dentry *h_dentry;
> +	int ret;
> +
> +	h_dentry = securityfs_create_file(h->name, 0600, parent,
> +			NULL, &krsi_hook_ops);
> +
> +	if (IS_ERR(h_dentry))
> +		return PTR_ERR(h_dentry);
> +	h_dentry->d_fsdata = h;
> +	h->h_dentry = h_dentry;
> +	return 0;
> +
> +error:

The 'error' label is not used here.

> +	securityfs_remove(h_dentry);
> +	return ret;
> +}
> +
> +static int __init krsi_fs_init(void)
> +{
> +
> +	struct krsi_hook *hook;
> +	int ret;
> +
> +	krsi_dir = securityfs_create_dir(KRSI_SFS_NAME, NULL);
> +	if (IS_ERR(krsi_dir)) {
> +		ret = PTR_ERR(krsi_dir);
> +		pr_err("Unable to create krsi sysfs dir: %d\n", ret);
> +		krsi_dir = NULL;
> +		return ret;
> +	}
> +
> +	/*
> +	 * If there is an error in initializing a hook, the initialization
> +	 * logic makes sure that it has been freed, but this means that
> +	 * cleanup should be called for all the other hooks. The cleanup
> +	 * logic handles uninitialized data.
> +	 */
> +	krsi_for_each_hook(hook) {
> +		ret = krsi_init_hook(hook, krsi_dir);
> +		if (ret < 0)
> +			goto error;
> +	}
> +
> +	krsi_fs_initialized = 1;
> +	return 0;
> +error:
> +	krsi_for_each_hook(hook)
> +		krsi_free_hook(hook);
> +	securityfs_remove(krsi_dir);
> +	return ret;
> +}
> +
> +late_initcall(krsi_fs_init);
>