linux内核态real cred,Linux内核源码分析 -- 更新当前进程的 cred -- commit_creds
浅析一下用来修改当前进程 cred 的函数 commit_creds
源码版本：Linux kernel 5.9.9
首先来看 cred 结构
/*
* The security context of a task
*
* The parts of the context break down into two categories:
*
* (1) The objective context of a task. These parts are used when some other
*task is attempting to affect this one.
*
* (2) The subjective context. These details are used when the task is acting
*upon another object, be that a file, a task, a key or whatever.
*
* Note that some members of this structure belong to both categories - the
* LSM security pointer for instance.
*
* A task has two security pointers. task->real_cred points to the objective
* context that defines that task's actual details. The objective part of this
* context is used whenever that task is acted upon.
*
* task->cred points to the subjective context that defines the details of how
* that task is going to act upon another object. This may be overridden
* temporarily to point to another security context, but normally points to the
* same context as task->real_cred.
*/
struct cred {
atomic_tusage;
#ifdef CONFIG_DEBUG_CREDENTIALS
atomic_tsubscribers;/* number of processes subscribed 使用这个 cred 的进程数*/
void*put_addr;
unsignedmagic;
#define CRED_MAGIC0x43736564
#define CRED_MAGIC_DEAD0x44656144
#endif
kuid_tuid;/* real UID of the task 创建进程的用户的 id ，不是创建可执行程序的用户 id*/
kgid_tgid;/* real GID of the task */
kuid_tsuid;/* saved UID of the task 保存的 euid 切换之前的 id，用于 euid 切换回来*/
kgid_tsgid;/* saved GID of the task */
kuid_teuid;/* effective UID of the task euid 是进程运行过程中实时的 id*/
kgid_tegid;/* effective GID of the task */
kuid_tfsuid;/* UID for VFS ops */
kgid_tfsgid;/* GID for VFS ops */
unsignedsecurebits;/* SUID-less security management */
kernel_cap_tcap_inheritable; /* caps our children can inherit */
kernel_cap_tcap_permitted;/* caps we're permitted */
kernel_cap_tcap_effective;/* caps we can actually use */
kernel_cap_tcap_bset;/* capability bounding set */
kernel_cap_tcap_ambient;/* Ambient capability set */
#ifdef CONFIG_KEYS
unsigned charjit_keyring;/* default keyring to attach requested
* keys to */
struct key*session_keyring; /* keyring inherited over fork */
struct key*process_keyring; /* keyring private to this process */
struct key*thread_keyring; /* keyring private to this thread */
struct key*request_key_auth; /* assumed request_key authority */
#endif
#ifdef CONFIG_SECURITY
void*security;/* subjective LSM security */
#endif
struct user_struct *user;/* real user ID subscription 创建进程的用户的 id 描述符*/
struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
struct group_info *group_info;/* supplementary groups for euid/fsgid */
/* RCU deletion */
union {
int non_rcu;/* Can we skip RCU deletion? */
struct rcu_headrcu;/* RCU deletion hook */
};
} __randomize_layout;
commit_creds
/**
* commit_creds - Install new cred