网站放自己服务器备案,东莞抖音推广,正方教务管理系统入口,网站宽度 超宽接前一篇文章#xff1a;Linux内核进程管理子系统有什么第三十九回 —— 进程主结构详解#xff08;35#xff09; 本文内容参考#xff1a;
Linux内核进程管理专题报告_linux rseq-CSDN博客
《趣谈Linux操作系统 核心原理篇#xff1a;第三部分 进程管理》—— 刘超
《…接前一篇文章Linux内核进程管理子系统有什么第三十九回 —— 进程主结构详解35 本文内容参考
Linux内核进程管理专题报告_linux rseq-CSDN博客
《趣谈Linux操作系统 核心原理篇第三部分 进程管理》—— 刘超
《图解Linux内核 基于6.x》 —— 姜亚华 机械工业出版社
特此致谢 进程管理核心结构 —— task_struct
8. 进程权限相关成员
进程权限相关成员包括以下几个 /* Process credentials: *//* Tracers credentials at attach: */const struct cred __rcu *ptracer_cred;/* Objective and real subjective task credentials (COW): */const struct cred __rcu *real_cred;/* Effective (overridable) subjective task credentials (COW): */const struct cred __rcu *cred;
这几个字段的描述如下 上一回开始对于struct cred进行解析本回继续。为了便于理解和回顾再次贴出struct cred的定义在include/linux/cred.h中如下
/** 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 tasks 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_t usage;
#ifdef CONFIG_DEBUG_CREDENTIALSatomic_t subscribers; /* number of processes subscribed */void *put_addr;unsigned magic;
#define CRED_MAGIC 0x43736564
#define CRED_MAGIC_DEAD 0x44656144
#endifkuid_t uid; /* real UID of the task */kgid_t gid; /* real GID of the task */kuid_t suid; /* saved UID of the task */kgid_t sgid; /* saved GID of the task */kuid_t euid; /* effective UID of the task */kgid_t egid; /* effective GID of the task */kuid_t fsuid; /* UID for VFS ops */kgid_t fsgid; /* GID for VFS ops */unsigned securebits; /* SUID-less security management */kernel_cap_t cap_inheritable; /* caps our children can inherit */kernel_cap_t cap_permitted; /* caps were permitted */kernel_cap_t cap_effective; /* caps we can actually use */kernel_cap_t cap_bset; /* capability bounding set */kernel_cap_t cap_ambient; /* Ambient capability set */
#ifdef CONFIG_KEYSunsigned char jit_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_SECURITYvoid *security; /* LSM security */
#endifstruct user_struct *user; /* real user ID subscription */struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */struct ucounts *ucounts;struct group_info *group_info; /* supplementary groups for euid/fsgid *//* RCU deletion */union {int non_rcu; /* Can we skip RCU deletion? */struct rcu_head rcu; /* RCU deletion hook */};
} __randomize_layout;
上一回讲到struct cred中的3组字段 一般来说fsuid、euid与uid是一样的fsgid、egid与gid也是一样的。因为谁启动的进程就应该审核启动者有没有相关权限。但是也存在特殊情况。例如
用户张三zhangsan想运行一个用户李四lisi安装的应用程序比如游戏、视频播放器等。由于是李四安装的当然该应用程序文件的权限是rwxr--r--。也就是说文件属主即文件所有者李四权限为可读、可写、可执行而属组同组用户权限为只可读组外其他用户权限也是只可读。
那么问题来了张三想运行该程序但没有可执行权限该怎么办呢需要向用户李四要授权。李四并无意见于是将应用程序文件的权限由rwxr--r--改为rwxr-xr-x。也就是分别给属组和组外权限加入了可执行。这样张三就可以正常运行程序了。
接下来问题又来了张三看着看着视频觉得不错想把这个视频存下来或者玩游戏过了几关想保存进度。一点下载或保存按钮坏了提示无权限。为什么会这样因为下载视频需要有保存路径的写入权限游戏玩家数据是保存在某个文件中的也需要写入权限。由于该文件只给所有者李四开了写入权限而进程的euid和fsuid都是张三那当然写不了了。
又该怎么解决这个问题呢可以通过chmod us xxx命令给这个应用程序设置set-user-id将它的权限变为rwsr-xr-x。此时张三再启动这个应用的时候创建的进程uid还是张三zhangsan但是euid和fsuid就不是张三了而是李四lisi。也就是说因为看到了set-user-id标识euid和fsuid就改为文件所有者即李四了。
关于chmod us命令详情参考以下文章
Linux命令 chmod 例chmod us-CSDN博客 更多内容请看下回。
