Continued from the previous article: LSM zero-knowledge learning 3. Implementation details of pile insertion principle (1)
References for the content of this article:
Analysis of LSM (Linux Security Modules) Framework Principles - lsm linux_pwl999's Blog - CSDN Blog
Thank you very much!
Two, security_file_open function context
The previous article mentioned that the vfs_open function in fs/open.c calls the do_dentry_open function in the same file, and the do_dentry_open function calls the security_file_open function. Post the code snippet again:
error = security_file_open(f);
if (error)
goto cleanup_all;The security_file_open function is in security/security.c, the code is as follows:
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);
}In fact, the security_file_open function is a stub function (Hook) of LSM, which is just a framework. When called, it will call all the functions on the corresponding linked list one by one.
Focus on the call_init_hook function, which is precisely a macro, which is defined in the same file (security/security.c), and the code is as follows:
#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; \
})
The actual expansion of call_int_hook(file_open, 0, file) is:
({ \
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; \
})The linked list corresponding to the open operation is security_hook_heads.file_open, and the P->hook.FUNC of the node (P->hook.file_open in this example) is a function pointer.
- hlist_for_each_entry
hlist_for_each_entry is a macro definition, in include/linux/list.h, the code is as follows:
/**
* 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))
The hlist_entry_safe macro is defined in the same file (just above), the code is as follows:
#define hlist_entry_safe(ptr, type, member) \
({ typeof(ptr) ____ptr = (ptr); \
____ptr ? hlist_entry(____ptr, type, member) : NULL; \
})The hlist_entry macro is of course also defined in the same file, the code is as follows:
#define hlist_entry(ptr, type, member) container_of(ptr,type,member)Expand hlist_for_each_entry step by step:
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; }) )Finally, the actual expansion of hlist_for_each_entry(P, &security_hook_heads.file_open, list) (correspondence: P corresponds to pos, &security_hook_heads.file_open corresponds to head, and list corresponds to member) is:
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; }) )First look at the type of (&security_hook_heads.file_open)->first. security_hook_heads is defined in security/security.c and its type is struct security_hook_heads. And struct security_hook_heads is defined in include/linux/lsm_hooks.h, the code is as follows:
struct security_hook_heads {
#define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;
#include "lsm_hook_defs.h"
#undef LSM_HOOK
} __randomize_layout;Looking at the header file included in the structure, we know that this structure must be a large structure with many members. Take a look at the contents of the include/linux/lsm_hook_defs.h file:
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Linux Security Module Hook declarations.
*
* Copyright (C) 2001 WireX Communications, Inc <[email protected]>
* Copyright (C) 2001 Greg Kroah-Hartman <[email protected]>
* Copyright (C) 2001 Networks Associates Technology, Inc <[email protected]>
* Copyright (C) 2001 James Morris <[email protected]>
* Copyright (C) 2001 Silicon Graphics, Inc. (Trust Technology Group)
* Copyright (C) 2015 Intel Corporation.
* Copyright (C) 2015 Casey Schaufler <[email protected]>
* 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 */
As you can see, there is the following line in the include/linux/lsm_hook_defs.h file:
LSM_HOOK(int, 0, file_open, struct file *file)The LSM_HOOK macro definition is above in struct security_hook_heads, let’s review its definition again:
#define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;Therefore, the above statement expands to:
struct hlist_head file_open;The struct hlist_head structure is defined in include/linux/types.h:
struct hlist_head {
struct hlist_node *first;
};In summary, the final type of (&security_hook_heads.file_open)->first is struct hlist_node.
Let me say a little more here, struct hlist_node is also defined in include/linux/types.h:
struct hlist_node {
struct hlist_node *next, **pprev;
};Let's look at the type of P again. The type of P has been clearly explained in the above call_init_hook, which is struct security_hook_list. struct security_hook_list is defined in include/linux/lsm_hooks.h, the code is as follows:
/*
* 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;Eventually the following segments are derived:
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; }) )That is, the final expansion of hlist_for_each_entry(P, &security_hook_heads.file_open, list) is:
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; }) )Let me add the definition of container_of here. In include/linux/container_of.h, the code is as follows:
/**
* 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))); })This incomprehensible place is actually
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; })and
P = ({ struct hlist_node ____(P)->list.next = ((P)->list.next); ____(P)->list.next ? container_of((P)->list.next), struct security_hook_list, list) : NULL; }) Why is there a multi-line assignment statement in the loop? The author also felt very at a loss when I first read it. At first I thought its function was to assign values to structures, but no matter how I looked at it, it didn't look like it. Later, I figured out that it is actually equivalent to executing multiple statements in one line, and assigning the value of the last statement to P.
The meaning of the previous statement is to first point to ((&security_hook_heads.file_open)->first), that is, the head pointer (struct hlist_nod type) of the linked list file_open (struct hlist_head type), return the pointer of the struct security_hook_list to which file_open->first belongs, and assign it to P (P is exactly the type of struct security_hook_list). The meaning of the latter statement is similar, except that what is returned is the pointer of the struct security_hook_list to which the (each) next item in this linked list belongs.