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


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);
>
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