LSM零知识学习四、插桩原理实现细节（2）
2024-05-11 03:11:09
接前一篇文章：LSM零知识学习三、插桩原理实现细节（1）
本文内容参考：
LSM(Linux Security Modules)框架原理解析_lsm linux_pwl999的博客-CSDN博客
特此致谢！
二、security_file_open函数上下文
前一篇文章讲到了fs/open.c中的vfs_open函数调用同文件中的do_dentry_open函数，do_dentry_open函数又调用了security_file_open函数。再次贴出代码片段：
error = security_file_open(f);
if (error)goto cleanup_all;security_file_open函数在security/security.c中，代码如下：
int security_file_open(struct file *file)
{int ret;ret = call_int_hook(file_open, 0, file);if (ret)return ret;return fsnotify_perm(file, MAY_OPEN);
}实际上，security_file_open函数就是一个LSM的桩函数（Hook），它只是一个框架，在被调用时会逐个调用对应链表上的所有函数。
重点关注call_init_hook函数准确地说是宏，其在同文件（security/security.c）中定义，代码如下：
#define call_int_hook(FUNC, IRC, ...) ({ \int RC = IRC; \do { \struct security_hook_list *P; \\hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \RC = P->hook.FUNC(__VA_ARGS__); \if (RC != 0) \break; \} \} while (0); \RC; \
})
实际展开call_int_hook(file_open, 0, file)为：
({ \int RC = IRC; \do { \struct security_hook_list *P; \\hlist_for_each_entry(P, &security_hook_heads.file_open, list) { \RC = P->hook.file_open(__VA_ARGS__); \if (RC != 0) \break; \} \} while (0); \RC; \
})open操作对应的链表为security_hook_heads.file_open，而结点的P->hook.FUNC（本例中为P->hook.file_open）为函数指针。
- hlist_for_each_entry
hlist_for_each_entry为宏定义，在include/linux/list.h中，代码如下：
/*** hlist_for_each_entry - iterate over list of given type* @pos: the type * to use as a loop cursor.* @head: the head for your list.* @member: the name of the hlist_node within the struct.*/
#define hlist_for_each_entry(pos, head, member) \for (pos = hlist_entry_safe((head)->first, typeof(*(pos)), member);\pos; \pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
hlist_entry_safe宏定义在同文件中（就在上边），代码如下：
#define hlist_entry_safe(ptr, type, member) \({ typeof(ptr) ____ptr = (ptr); \____ptr ? hlist_entry(____ptr, type, member) : NULL; \})hlist_entry宏当然也在同文件中定义，代码如下：
#define hlist_entry(ptr, type, member) container_of(ptr,type,member)将hlist_for_each_entry一步步展开：
for (pos = hlist_entry_safe((head)->first, typeof(*(pos)), member);\pos; \pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))for (pos = ({ typeof((head)->first) ____(head)->first = ((head)->first); ____(head)->first ? hlist_entry(____(head)->first, typeof(*(pos)), member) : NULL; }); \pos; \pos = ({ typeof((pos)->member.next) ____(pos)->member.next = ((pos)->member.next); ____(pos)->member.next ? hlist_entry((pos)->member.next), typeof(*(pos)), member) : NULL; }) )for (pos = ({ typeof((head)->first) ____(head)->first = ((head)->first); ____(head)->first ? container_of(____(head)->first, typeof(*(pos)), member) : NULL; }); \pos; \pos = ({ typeof((pos)->member.next) ____(pos)->member.next = ((pos)->member.next); ____(pos)->member.next ? container_of((pos)->member.next), typeof(*(pos)), member) : NULL; }) )最后hlist_for_each_entry(P, &security_hook_heads.file_open, list)实际展开（对应关系：P对应pos，&security_hook_heads.file_open对应head，list对应member）为：
for (P = ({ typeof((&security_hook_heads.file_open)->first) ____(&security_hook_heads.file_open)->first = ((&security_hook_heads.file_open)->first); ____(&security_hook_heads.file_open)->first ? container_of(____(&security_hook_heads.file_open)->first, typeof(*(P)), list) : NULL; }); \P; \P = ({ typeof((P)->list.next) ____(P)->list.next = ((P)->list.next); ____(P)->list.next ? container_of((P)->list.next), typeof(*(P)), list) : NULL; }) )先来看一下(&security_hook_heads.file_open)->first的类型。security_hook_heads在security/security.c中定义，其类型为struct security_hook_heads。而struct security_hook_heads在include/linux/lsm_hooks.h中定义，代码如下：
struct security_hook_heads {#define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;#include "lsm_hook_defs.h"#undef LSM_HOOK
} __randomize_layout;一看结构体中包含头文件，就知道这个结构体准是一个大结构体，成员有很多。看一下include/linux/lsm_hook_defs.h文件的内容：
/* SPDX-License-Identifier: GPL-2.0 *//** Linux Security Module Hook declarations.** Copyright (C) 2001 WireX Communications, Inc <chris@wirex.com>* Copyright (C) 2001 Greg Kroah-Hartman <greg@kroah.com>* Copyright (C) 2001 Networks Associates Technology, Inc <ssmalley@nai.com>* Copyright (C) 2001 James Morris <jmorris@intercode.com.au>* Copyright (C) 2001 Silicon Graphics, Inc. (Trust Technology Group)* Copyright (C) 2015 Intel Corporation.* Copyright (C) 2015 Casey Schaufler <casey@schaufler-ca.com>* Copyright (C) 2016 Mellanox Techonologies* Copyright (C) 2020 Google LLC.*//** The macro LSM_HOOK is used to define the data structures required by* the LSM framework using the pattern:** LSM_HOOK(<return_type>, <default_value>, <hook_name>, args...)** struct security_hook_heads {* #define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;* #include <linux/lsm_hook_defs.h>* #undef LSM_HOOK* };*/
LSM_HOOK(int, 0, binder_set_context_mgr, const struct cred *mgr)
LSM_HOOK(int, 0, binder_transaction, const struct cred *from,const struct cred *to)
LSM_HOOK(int, 0, binder_transfer_binder, const struct cred *from,const struct cred *to)
LSM_HOOK(int, 0, binder_transfer_file, const struct cred *from,const struct cred *to, struct file *file)
LSM_HOOK(int, 0, ptrace_access_check, struct task_struct *child,unsigned int mode)
LSM_HOOK(int, 0, ptrace_traceme, struct task_struct *parent)
LSM_HOOK(int, 0, capget, struct task_struct *target, kernel_cap_t *effective,kernel_cap_t *inheritable, kernel_cap_t *permitted)
LSM_HOOK(int, 0, capset, struct cred *new, const struct cred *old,const kernel_cap_t *effective, const kernel_cap_t *inheritable,const kernel_cap_t *permitted)
LSM_HOOK(int, 0, capable, const struct cred *cred, struct user_namespace *ns,int cap, unsigned int opts)
LSM_HOOK(int, 0, quotactl, int cmds, int type, int id, struct super_block *sb)
LSM_HOOK(int, 0, quota_on, struct dentry *dentry)
LSM_HOOK(int, 0, syslog, int type)
LSM_HOOK(int, 0, settime, const struct timespec64 *ts,const struct timezone *tz)
LSM_HOOK(int, 0, vm_enough_memory, struct mm_struct *mm, long pages)
LSM_HOOK(int, 0, bprm_creds_for_exec, struct linux_binprm *bprm)
LSM_HOOK(int, 0, bprm_creds_from_file, struct linux_binprm *bprm, struct file *file)
LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm)
LSM_HOOK(void, LSM_RET_VOID, bprm_committing_creds, struct linux_binprm *bprm)
LSM_HOOK(void, LSM_RET_VOID, bprm_committed_creds, struct linux_binprm *bprm)
LSM_HOOK(int, 0, fs_context_dup, struct fs_context *fc,struct fs_context *src_sc)
LSM_HOOK(int, -ENOPARAM, fs_context_parse_param, struct fs_context *fc,struct fs_parameter *param)
LSM_HOOK(int, 0, sb_alloc_security, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_delete, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_free_security, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_free_mnt_opts, void *mnt_opts)
LSM_HOOK(int, 0, sb_eat_lsm_opts, char *orig, void **mnt_opts)
LSM_HOOK(int, 0, sb_mnt_opts_compat, struct super_block *sb, void *mnt_opts)
LSM_HOOK(int, 0, sb_remount, struct super_block *sb, void *mnt_opts)
LSM_HOOK(int, 0, sb_kern_mount, struct super_block *sb)
LSM_HOOK(int, 0, sb_show_options, struct seq_file *m, struct super_block *sb)
LSM_HOOK(int, 0, sb_statfs, struct dentry *dentry)
LSM_HOOK(int, 0, sb_mount, const char *dev_name, const struct path *path,const char *type, unsigned long flags, void *data)
LSM_HOOK(int, 0, sb_umount, struct vfsmount *mnt, int flags)
LSM_HOOK(int, 0, sb_pivotroot, const struct path *old_path,const struct path *new_path)
LSM_HOOK(int, 0, sb_set_mnt_opts, struct super_block *sb, void *mnt_opts,unsigned long kern_flags, unsigned long *set_kern_flags)
LSM_HOOK(int, 0, sb_clone_mnt_opts, const struct super_block *oldsb,struct super_block *newsb, unsigned long kern_flags,unsigned long *set_kern_flags)
LSM_HOOK(int, 0, move_mount, const struct path *from_path,const struct path *to_path)
LSM_HOOK(int, -EOPNOTSUPP, dentry_init_security, struct dentry *dentry,int mode, const struct qstr *name, const char **xattr_name,void **ctx, u32 *ctxlen)
LSM_HOOK(int, 0, dentry_create_files_as, struct dentry *dentry, int mode,struct qstr *name, const struct cred *old, struct cred *new)#ifdef CONFIG_SECURITY_PATH
LSM_HOOK(int, 0, path_unlink, const struct path *dir, struct dentry *dentry)
LSM_HOOK(int, 0, path_mkdir, const struct path *dir, struct dentry *dentry,umode_t mode)
LSM_HOOK(int, 0, path_rmdir, const struct path *dir, struct dentry *dentry)
LSM_HOOK(int, 0, path_mknod, const struct path *dir, struct dentry *dentry,umode_t mode, unsigned int dev)
LSM_HOOK(int, 0, path_truncate, const struct path *path)
LSM_HOOK(int, 0, path_symlink, const struct path *dir, struct dentry *dentry,const char *old_name)
LSM_HOOK(int, 0, path_link, struct dentry *old_dentry,const struct path *new_dir, struct dentry *new_dentry)
LSM_HOOK(int, 0, path_rename, const struct path *old_dir,struct dentry *old_dentry, const struct path *new_dir,struct dentry *new_dentry, unsigned int flags)
LSM_HOOK(int, 0, path_chmod, const struct path *path, umode_t mode)
LSM_HOOK(int, 0, path_chown, const struct path *path, kuid_t uid, kgid_t gid)
LSM_HOOK(int, 0, path_chroot, const struct path *path)
#endif /* CONFIG_SECURITY_PATH *//* Needed for inode based security check */
LSM_HOOK(int, 0, path_notify, const struct path *path, u64 mask,unsigned int obj_type)
LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode)
LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
LSM_HOOK(int, 0, inode_init_security, struct inode *inode,struct inode *dir, const struct qstr *qstr, const char **name,void **value, size_t *len)
LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,const struct qstr *name, const struct inode *context_inode)
LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,umode_t mode)
LSM_HOOK(int, 0, inode_link, struct dentry *old_dentry, struct inode *dir,struct dentry *new_dentry)
LSM_HOOK(int, 0, inode_unlink, struct inode *dir, struct dentry *dentry)
LSM_HOOK(int, 0, inode_symlink, struct inode *dir, struct dentry *dentry,const char *old_name)
LSM_HOOK(int, 0, inode_mkdir, struct inode *dir, struct dentry *dentry,umode_t mode)
LSM_HOOK(int, 0, inode_rmdir, struct inode *dir, struct dentry *dentry)
LSM_HOOK(int, 0, inode_mknod, struct inode *dir, struct dentry *dentry,umode_t mode, dev_t dev)
LSM_HOOK(int, 0, inode_rename, struct inode *old_dir, struct dentry *old_dentry,struct inode *new_dir, struct dentry *new_dentry)
LSM_HOOK(int, 0, inode_readlink, struct dentry *dentry)
LSM_HOOK(int, 0, inode_follow_link, struct dentry *dentry, struct inode *inode,bool rcu)
LSM_HOOK(int, 0, inode_permission, struct inode *inode, int mask)
LSM_HOOK(int, 0, inode_setattr, struct dentry *dentry, struct iattr *attr)
LSM_HOOK(int, 0, inode_getattr, const struct path *path)
LSM_HOOK(int, 0, inode_setxattr, struct user_namespace *mnt_userns,struct dentry *dentry, const char *name, const void *value,size_t size, int flags)
LSM_HOOK(void, LSM_RET_VOID, inode_post_setxattr, struct dentry *dentry,const char *name, const void *value, size_t size, int flags)
LSM_HOOK(int, 0, inode_getxattr, struct dentry *dentry, const char *name)
LSM_HOOK(int, 0, inode_listxattr, struct dentry *dentry)
LSM_HOOK(int, 0, inode_removexattr, struct user_namespace *mnt_userns,struct dentry *dentry, const char *name)
LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry)
LSM_HOOK(int, 0, inode_killpriv, struct user_namespace *mnt_userns,struct dentry *dentry)
LSM_HOOK(int, -EOPNOTSUPP, inode_getsecurity, struct user_namespace *mnt_userns,struct inode *inode, const char *name, void **buffer, bool alloc)
LSM_HOOK(int, -EOPNOTSUPP, inode_setsecurity, struct inode *inode,const char *name, const void *value, size_t size, int flags)
LSM_HOOK(int, 0, inode_listsecurity, struct inode *inode, char *buffer,size_t buffer_size)
LSM_HOOK(void, LSM_RET_VOID, inode_getsecid, struct inode *inode, u32 *secid)
LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, const char *name)
LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,struct kernfs_node *kn)
LSM_HOOK(int, 0, file_permission, struct file *file, int mask)
LSM_HOOK(int, 0, file_alloc_security, struct file *file)
LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,unsigned long arg)
LSM_HOOK(int, 0, mmap_addr, unsigned long addr)
LSM_HOOK(int, 0, mmap_file, struct file *file, unsigned long reqprot,unsigned long prot, unsigned long flags)
LSM_HOOK(int, 0, file_mprotect, struct vm_area_struct *vma,unsigned long reqprot, unsigned long prot)
LSM_HOOK(int, 0, file_lock, struct file *file, unsigned int cmd)
LSM_HOOK(int, 0, file_fcntl, struct file *file, unsigned int cmd,unsigned long arg)
LSM_HOOK(void, LSM_RET_VOID, file_set_fowner, struct file *file)
LSM_HOOK(int, 0, file_send_sigiotask, struct task_struct *tsk,struct fown_struct *fown, int sig)
LSM_HOOK(int, 0, file_receive, struct file *file)
LSM_HOOK(int, 0, file_open, struct file *file)
LSM_HOOK(int, 0, task_alloc, struct task_struct *task,unsigned long clone_flags)
LSM_HOOK(void, LSM_RET_VOID, task_free, struct task_struct *task)
LSM_HOOK(int, 0, cred_alloc_blank, struct cred *cred, gfp_t gfp)
LSM_HOOK(void, LSM_RET_VOID, cred_free, struct cred *cred)
LSM_HOOK(int, 0, cred_prepare, struct cred *new, const struct cred *old,gfp_t gfp)
LSM_HOOK(void, LSM_RET_VOID, cred_transfer, struct cred *new,const struct cred *old)
LSM_HOOK(void, LSM_RET_VOID, cred_getsecid, const struct cred *c, u32 *secid)
LSM_HOOK(int, 0, kernel_act_as, struct cred *new, u32 secid)
LSM_HOOK(int, 0, kernel_create_files_as, struct cred *new, struct inode *inode)
LSM_HOOK(int, 0, kernel_module_request, char *kmod_name)
LSM_HOOK(int, 0, kernel_load_data, enum kernel_load_data_id id, bool contents)
LSM_HOOK(int, 0, kernel_post_load_data, char *buf, loff_t size,enum kernel_load_data_id id, char *description)
LSM_HOOK(int, 0, kernel_read_file, struct file *file,enum kernel_read_file_id id, bool contents)
LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,loff_t size, enum kernel_read_file_id id)
LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old,int flags)
LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,int flags)
LSM_HOOK(int, 0, task_fix_setgroups, struct cred *new, const struct cred * old)
LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
LSM_HOOK(int, 0, task_getsid, struct task_struct *p)
LSM_HOOK(void, LSM_RET_VOID, current_getsecid_subj, u32 *secid)
LSM_HOOK(void, LSM_RET_VOID, task_getsecid_obj,struct task_struct *p, u32 *secid)
LSM_HOOK(int, 0, task_setnice, struct task_struct *p, int nice)
LSM_HOOK(int, 0, task_setioprio, struct task_struct *p, int ioprio)
LSM_HOOK(int, 0, task_getioprio, struct task_struct *p)
LSM_HOOK(int, 0, task_prlimit, const struct cred *cred,const struct cred *tcred, unsigned int flags)
LSM_HOOK(int, 0, task_setrlimit, struct task_struct *p, unsigned int resource,struct rlimit *new_rlim)
LSM_HOOK(int, 0, task_setscheduler, struct task_struct *p)
LSM_HOOK(int, 0, task_getscheduler, struct task_struct *p)
LSM_HOOK(int, 0, task_movememory, struct task_struct *p)
LSM_HOOK(int, 0, task_kill, struct task_struct *p, struct kernel_siginfo *info,int sig, const struct cred *cred)
LSM_HOOK(int, -ENOSYS, task_prctl, int option, unsigned long arg2,unsigned long arg3, unsigned long arg4, unsigned long arg5)
LSM_HOOK(void, LSM_RET_VOID, task_to_inode, struct task_struct *p,struct inode *inode)
LSM_HOOK(int, 0, userns_create, const struct cred *cred)
LSM_HOOK(int, 0, ipc_permission, struct kern_ipc_perm *ipcp, short flag)
LSM_HOOK(void, LSM_RET_VOID, ipc_getsecid, struct kern_ipc_perm *ipcp,u32 *secid)
LSM_HOOK(int, 0, msg_msg_alloc_security, struct msg_msg *msg)
LSM_HOOK(void, LSM_RET_VOID, msg_msg_free_security, struct msg_msg *msg)
LSM_HOOK(int, 0, msg_queue_alloc_security, struct kern_ipc_perm *perm)
LSM_HOOK(void, LSM_RET_VOID, msg_queue_free_security,struct kern_ipc_perm *perm)
LSM_HOOK(int, 0, msg_queue_associate, struct kern_ipc_perm *perm, int msqflg)
LSM_HOOK(int, 0, msg_queue_msgctl, struct kern_ipc_perm *perm, int cmd)
LSM_HOOK(int, 0, msg_queue_msgsnd, struct kern_ipc_perm *perm,struct msg_msg *msg, int msqflg)
LSM_HOOK(int, 0, msg_queue_msgrcv, struct kern_ipc_perm *perm,struct msg_msg *msg, struct task_struct *target, long type, int mode)
LSM_HOOK(int, 0, shm_alloc_security, struct kern_ipc_perm *perm)
LSM_HOOK(void, LSM_RET_VOID, shm_free_security, struct kern_ipc_perm *perm)
LSM_HOOK(int, 0, shm_associate, struct kern_ipc_perm *perm, int shmflg)
LSM_HOOK(int, 0, shm_shmctl, struct kern_ipc_perm *perm, int cmd)
LSM_HOOK(int, 0, shm_shmat, struct kern_ipc_perm *perm, char __user *shmaddr,int shmflg)
LSM_HOOK(int, 0, sem_alloc_security, struct kern_ipc_perm *perm)
LSM_HOOK(void, LSM_RET_VOID, sem_free_security, struct kern_ipc_perm *perm)
LSM_HOOK(int, 0, sem_associate, struct kern_ipc_perm *perm, int semflg)
LSM_HOOK(int, 0, sem_semctl, struct kern_ipc_perm *perm, int cmd)
LSM_HOOK(int, 0, sem_semop, struct kern_ipc_perm *perm, struct sembuf *sops,unsigned nsops, int alter)
LSM_HOOK(int, 0, netlink_send, struct sock *sk, struct sk_buff *skb)
LSM_HOOK(void, LSM_RET_VOID, d_instantiate, struct dentry *dentry,struct inode *inode)
LSM_HOOK(int, -EINVAL, getprocattr, struct task_struct *p, const char *name,char **value)
LSM_HOOK(int, -EINVAL, setprocattr, const char *name, void *value, size_t size)
LSM_HOOK(int, 0, ismaclabel, const char *name)
LSM_HOOK(int, -EOPNOTSUPP, secid_to_secctx, u32 secid, char **secdata,u32 *seclen)
LSM_HOOK(int, 0, secctx_to_secid, const char *secdata, u32 seclen, u32 *secid)
LSM_HOOK(void, LSM_RET_VOID, release_secctx, char *secdata, u32 seclen)
LSM_HOOK(void, LSM_RET_VOID, inode_invalidate_secctx, struct inode *inode)
LSM_HOOK(int, 0, inode_notifysecctx, struct inode *inode, void *ctx, u32 ctxlen)
LSM_HOOK(int, 0, inode_setsecctx, struct dentry *dentry, void *ctx, u32 ctxlen)
LSM_HOOK(int, 0, inode_getsecctx, struct inode *inode, void **ctx,u32 *ctxlen)#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
LSM_HOOK(int, 0, post_notification, const struct cred *w_cred,const struct cred *cred, struct watch_notification *n)
#endif /* CONFIG_SECURITY && CONFIG_WATCH_QUEUE */#if defined(CONFIG_SECURITY) && defined(CONFIG_KEY_NOTIFICATIONS)
LSM_HOOK(int, 0, watch_key, struct key *key)
#endif /* CONFIG_SECURITY && CONFIG_KEY_NOTIFICATIONS */#ifdef CONFIG_SECURITY_NETWORK
LSM_HOOK(int, 0, unix_stream_connect, struct sock *sock, struct sock *other,struct sock *newsk)
LSM_HOOK(int, 0, unix_may_send, struct socket *sock, struct socket *other)
LSM_HOOK(int, 0, socket_create, int family, int type, int protocol, int kern)
LSM_HOOK(int, 0, socket_post_create, struct socket *sock, int family, int type,int protocol, int kern)
LSM_HOOK(int, 0, socket_socketpair, struct socket *socka, struct socket *sockb)
LSM_HOOK(int, 0, socket_bind, struct socket *sock, struct sockaddr *address,int addrlen)
LSM_HOOK(int, 0, socket_connect, struct socket *sock, struct sockaddr *address,int addrlen)
LSM_HOOK(int, 0, socket_listen, struct socket *sock, int backlog)
LSM_HOOK(int, 0, socket_accept, struct socket *sock, struct socket *newsock)
LSM_HOOK(int, 0, socket_sendmsg, struct socket *sock, struct msghdr *msg,int size)
LSM_HOOK(int, 0, socket_recvmsg, struct socket *sock, struct msghdr *msg,int size, int flags)
LSM_HOOK(int, 0, socket_getsockname, struct socket *sock)
LSM_HOOK(int, 0, socket_getpeername, struct socket *sock)
LSM_HOOK(int, 0, socket_getsockopt, struct socket *sock, int level, int optname)
LSM_HOOK(int, 0, socket_setsockopt, struct socket *sock, int level, int optname)
LSM_HOOK(int, 0, socket_shutdown, struct socket *sock, int how)
LSM_HOOK(int, 0, socket_sock_rcv_skb, struct sock *sk, struct sk_buff *skb)
LSM_HOOK(int, 0, socket_getpeersec_stream, struct socket *sock,char __user *optval, int __user *optlen, unsigned len)
LSM_HOOK(int, 0, socket_getpeersec_dgram, struct socket *sock,struct sk_buff *skb, u32 *secid)
LSM_HOOK(int, 0, sk_alloc_security, struct sock *sk, int family, gfp_t priority)
LSM_HOOK(void, LSM_RET_VOID, sk_free_security, struct sock *sk)
LSM_HOOK(void, LSM_RET_VOID, sk_clone_security, const struct sock *sk,struct sock *newsk)
LSM_HOOK(void, LSM_RET_VOID, sk_getsecid, struct sock *sk, u32 *secid)
LSM_HOOK(void, LSM_RET_VOID, sock_graft, struct sock *sk, struct socket *parent)
LSM_HOOK(int, 0, inet_conn_request, const struct sock *sk, struct sk_buff *skb,struct request_sock *req)
LSM_HOOK(void, LSM_RET_VOID, inet_csk_clone, struct sock *newsk,const struct request_sock *req)
LSM_HOOK(void, LSM_RET_VOID, inet_conn_established, struct sock *sk,struct sk_buff *skb)
LSM_HOOK(int, 0, secmark_relabel_packet, u32 secid)
LSM_HOOK(void, LSM_RET_VOID, secmark_refcount_inc, void)
LSM_HOOK(void, LSM_RET_VOID, secmark_refcount_dec, void)
LSM_HOOK(void, LSM_RET_VOID, req_classify_flow, const struct request_sock *req,struct flowi_common *flic)
LSM_HOOK(int, 0, tun_dev_alloc_security, void **security)
LSM_HOOK(void, LSM_RET_VOID, tun_dev_free_security, void *security)
LSM_HOOK(int, 0, tun_dev_create, void)
LSM_HOOK(int, 0, tun_dev_attach_queue, void *security)
LSM_HOOK(int, 0, tun_dev_attach, struct sock *sk, void *security)
LSM_HOOK(int, 0, tun_dev_open, void *security)
LSM_HOOK(int, 0, sctp_assoc_request, struct sctp_association *asoc,struct sk_buff *skb)
LSM_HOOK(int, 0, sctp_bind_connect, struct sock *sk, int optname,struct sockaddr *address, int addrlen)
LSM_HOOK(void, LSM_RET_VOID, sctp_sk_clone, struct sctp_association *asoc,struct sock *sk, struct sock *newsk)
LSM_HOOK(int, 0, sctp_assoc_established, struct sctp_association *asoc,struct sk_buff *skb)
#endif /* CONFIG_SECURITY_NETWORK */#ifdef CONFIG_SECURITY_INFINIBAND
LSM_HOOK(int, 0, ib_pkey_access, void *sec, u64 subnet_prefix, u16 pkey)
LSM_HOOK(int, 0, ib_endport_manage_subnet, void *sec, const char *dev_name,u8 port_num)
LSM_HOOK(int, 0, ib_alloc_security, void **sec)
LSM_HOOK(void, LSM_RET_VOID, ib_free_security, void *sec)
#endif /* CONFIG_SECURITY_INFINIBAND */#ifdef CONFIG_SECURITY_NETWORK_XFRM
LSM_HOOK(int, 0, xfrm_policy_alloc_security, struct xfrm_sec_ctx **ctxp,struct xfrm_user_sec_ctx *sec_ctx, gfp_t gfp)
LSM_HOOK(int, 0, xfrm_policy_clone_security, struct xfrm_sec_ctx *old_ctx,struct xfrm_sec_ctx **new_ctx)
LSM_HOOK(void, LSM_RET_VOID, xfrm_policy_free_security,struct xfrm_sec_ctx *ctx)
LSM_HOOK(int, 0, xfrm_policy_delete_security, struct xfrm_sec_ctx *ctx)
LSM_HOOK(int, 0, xfrm_state_alloc, struct xfrm_state *x,struct xfrm_user_sec_ctx *sec_ctx)
LSM_HOOK(int, 0, xfrm_state_alloc_acquire, struct xfrm_state *x,struct xfrm_sec_ctx *polsec, u32 secid)
LSM_HOOK(void, LSM_RET_VOID, xfrm_state_free_security, struct xfrm_state *x)
LSM_HOOK(int, 0, xfrm_state_delete_security, struct xfrm_state *x)
LSM_HOOK(int, 0, xfrm_policy_lookup, struct xfrm_sec_ctx *ctx, u32 fl_secid)
LSM_HOOK(int, 1, xfrm_state_pol_flow_match, struct xfrm_state *x,struct xfrm_policy *xp, const struct flowi_common *flic)
LSM_HOOK(int, 0, xfrm_decode_session, struct sk_buff *skb, u32 *secid,int ckall)
#endif /* CONFIG_SECURITY_NETWORK_XFRM *//* key management security hooks */
#ifdef CONFIG_KEYS
LSM_HOOK(int, 0, key_alloc, struct key *key, const struct cred *cred,unsigned long flags)
LSM_HOOK(void, LSM_RET_VOID, key_free, struct key *key)
LSM_HOOK(int, 0, key_permission, key_ref_t key_ref, const struct cred *cred,enum key_need_perm need_perm)
LSM_HOOK(int, 0, key_getsecurity, struct key *key, char **_buffer)
#endif /* CONFIG_KEYS */#ifdef CONFIG_AUDIT
LSM_HOOK(int, 0, audit_rule_init, u32 field, u32 op, char *rulestr,void **lsmrule)
LSM_HOOK(int, 0, audit_rule_known, struct audit_krule *krule)
LSM_HOOK(int, 0, audit_rule_match, u32 secid, u32 field, u32 op, void *lsmrule)
LSM_HOOK(void, LSM_RET_VOID, audit_rule_free, void *lsmrule)
#endif /* CONFIG_AUDIT */#ifdef CONFIG_BPF_SYSCALL
LSM_HOOK(int, 0, bpf, int cmd, union bpf_attr *attr, unsigned int size)
LSM_HOOK(int, 0, bpf_map, struct bpf_map *map, fmode_t fmode)
LSM_HOOK(int, 0, bpf_prog, struct bpf_prog *prog)
LSM_HOOK(int, 0, bpf_map_alloc_security, struct bpf_map *map)
LSM_HOOK(void, LSM_RET_VOID, bpf_map_free_security, struct bpf_map *map)
LSM_HOOK(int, 0, bpf_prog_alloc_security, struct bpf_prog_aux *aux)
LSM_HOOK(void, LSM_RET_VOID, bpf_prog_free_security, struct bpf_prog_aux *aux)
#endif /* CONFIG_BPF_SYSCALL */LSM_HOOK(int, 0, locked_down, enum lockdown_reason what)#ifdef CONFIG_PERF_EVENTS
LSM_HOOK(int, 0, perf_event_open, struct perf_event_attr *attr, int type)
LSM_HOOK(int, 0, perf_event_alloc, struct perf_event *event)
LSM_HOOK(void, LSM_RET_VOID, perf_event_free, struct perf_event *event)
LSM_HOOK(int, 0, perf_event_read, struct perf_event *event)
LSM_HOOK(int, 0, perf_event_write, struct perf_event *event)
#endif /* CONFIG_PERF_EVENTS */#ifdef CONFIG_IO_URING
LSM_HOOK(int, 0, uring_override_creds, const struct cred *new)
LSM_HOOK(int, 0, uring_sqpoll, void)
LSM_HOOK(int, 0, uring_cmd, struct io_uring_cmd *ioucmd)
#endif /* CONFIG_IO_URING */
可以看到，include/linux/lsm_hook_defs.h文件中有以下一行：
LSM_HOOK(int, 0, file_open, struct file *file)LSM_HOOK宏定义就在上边在struct security_hook_heads中，再来回顾一下其定义：
#define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;因此，上述语句展开为：
struct hlist_head file_open;struct hlist_head结构体在include/linux/types.h中定义：
struct hlist_head {struct hlist_node *first;
};综上，最终得到(&security_hook_heads.file_open)->first的类型为struct hlist_node。
这里多说一点，struct hlist_node同样在include/linux/types.h中定义：
struct hlist_node {struct hlist_node *next, **pprev;
};再来看一下P的类型。P的类型在上边call_init_hook中已经交代得很清楚了，为struct security_hook_list。struct security_hook_list在include/linux/lsm_hooks.h中定义，代码如下：
/** Security module hook list structure.* For use with generic list macros for common operations.*/
struct security_hook_list {struct hlist_node list;struct hlist_head *head;union security_list_options hook;const char *lsm;
} __randomize_layout;最终推导出以下段：
for (P = ({ typeof((&security_hook_heads.file_open)->first) ____(&security_hook_heads.file_open)->first = ((&security_hook_heads.file_open)->first); ____(&security_hook_heads.file_open)->first ? container_of(____(&security_hook_heads.file_open)->first, typeof(*(P)), list) : NULL; }); \P; \P = ({ typeof((P)->list.next) ____(P)->list.next = ((P)->list.next); ____(P)->list.next ? container_of((P)->list.next), typeof(*(P)), list) : NULL; }) )即hlist_for_each_entry(P, &security_hook_heads.file_open, list)的终极展开为：
for (P = ({ struct hlist_node ____(&security_hook_heads.file_open)->first = ((&security_hook_heads.file_open)->first); ____(&security_hook_heads.file_open)->first ? container_of(____(&security_hook_heads.file_open)->first, struct security_hook_list, list) : NULL; }); \P; \P = ({ struct hlist_node ____(P)->list.next = ((P)->list.next); ____(P)->list.next ? container_of((P)->list.next), struct security_hook_list, list) : NULL; }) )这里再补充一下container_of的定义，在include/linux/container_of.h中，代码如下：
/*** container_of - cast a member of a structure out to the containing structure* @ptr: the pointer to the member.* @type: the type of the container struct this is embedded in.* @member: the name of the member within the struct.**/
#define container_of(ptr, type, member) ({ \void *__mptr = (void *)(ptr); \static_assert(__same_type(*(ptr), ((type *)0)->member) || \__same_type(*(ptr), void), \"pointer type mismatch in container_of()"); \((type *)(__mptr - offsetof(type, member))); })这段费解的地方其实就是
P = ({ struct hlist_node ____(&security_hook_heads.file_open)->first = ((&security_hook_heads.file_open)->first); ____(&security_hook_heads.file_open)->first ? container_of(____(&security_hook_heads.file_open)->first, struct security_hook_list, list) : NULL; })和
P = ({ struct hlist_node ____(P)->list.next = ((P)->list.next); ____(P)->list.next ? container_of((P)->list.next), struct security_hook_list, list) : NULL; }) 怎么循环中还带多行赋值语句？笔者开始看也觉得很茫然，一开始还以为其作用是结构体赋值，不过怎么看怎么不像。后来弄明白了，实际上就相当于一行中执行多个语句，把最后一个语句的值赋给P。
前一个语句的意思是先指向((&security_hook_heads.file_open)->first)，即链表file_open（struct hlist_head类型）的头指针（struct hlist_nod类型），返回file_open->first所属的struct security_hook_list的指针，赋给P（P正是struct security_hook_list类型）。后一个语句的意思类似，只是返回的是这个链表中的（各个）next项所属的struct security_hook_list的指针。
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