uid before unshare:5000 uid after unshare:0 Grant pt Error: : Permission denied
代码：
#define _GNU_SOURCE
#include <sys/mount.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <sched.h>
void set_uid_map(pid_t pid,int inside_id,int outside_id,int length) {
char path[256];
sprintf(path,"/proc/%d/uid_map",getpid());
FILE* uid_map = fopen(path,"w");
fprintf(uid_map,"%d %d %d",inside_id,outside_id,length);
fclose(uid_map);
}
void set_gid_map(pid_t pid,"/proc/%d/gid_map",getpid());
FILE* gid_map = fopen(path,"w");
fprintf(gid_map,length);
fclose(gid_map);
}
int main(void)
{
int master;
int flag = 0;
flag |= CLONE_NEWUSER;
flag |= CLONE_NEWNS;
flag |= CLONE_NEWIPC;
flag |= CLONE_NEWNET;
flag |= CLONE_NEWUTS;
flag |= CLONE_NEWPID;
printf("uid before unshare:%d \n",(int) getuid());
unshare(flag);
set_uid_map(getpid(),5000,1);
set_gid_map(getpid(),1);
printf("uid after unshare:%d \n",(int) getuid());
if ( ( master = posix_openpt(O_RDWR | O_NOCTTY) ) < 0)
perror("Openpt Error: ");
if ( grantpt(master) < 0 )
perror("Grant pt Error: ");
unlockpt(master);
return 0;
} // main
如果我删除标志| = CLONE_NEWUSER,没有报告错误.你能帮忙解释为什么会发生这种情况吗？提前致谢！
解决方法
grantpt(3)尝试确保从属伪终端将其组设置为特殊的tty组(或编译glibc时的任何TTY_GROUP)：
static int tty_gid = -1;
if (__glibc_unlikely (tty_gid == -1))
{
char *grtmpbuf;
struct group grbuf;
size_t grbuflen = __sysconf (_SC_GETGR_R_SIZE_MAX);
struct group *p;
/* Get the group ID of the special `tty' group. */
if (grbuflen == (size_t) -1L)
/* `sysconf' does not support _SC_GETGR_R_SIZE_MAX.
Try a moderate value. */
grbuflen = 1024;
grtmpbuf = (char *) __alloca (grbuflen);
__getgrnam_r (TTY_GROUP,&grbuf,grtmpbuf,grbuflen,&p);
if (p != NULL)
tty_gid = p->gr_gid;
}
gid_t gid = tty_gid == -1 ? __getgid () : tty_gid;
/* Make sure the group of the device is that special group. */
if (st.st_gid != gid)
{
if (__chown (buf,uid,gid) < 0)
goto helper;
}
见https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/grantpt.c;h=c04c85d450f9296efa506121bcee022afda3e2dd;hb=HEAD#l137.
在我的系统上,tty组是5.但是,该组没有映射到您的用户名空间,并且chown(2)失败,因为GID 5不存在. glibc然后落回执行pt_chown帮助器,这也是失败的.我没有看到为什么它失败的细节,但我认为这是因为它是setuid的人,除非你将root用户映射到您的用户名称空间.这里是显示失败操作的strace输出：
[pid 30] chown("/dev/pts/36",1000,5) = -1 EINVAL (Invalid argument)
给你几种方法来解决这个问题：
>映射所需的组(即tty),如果打开用户命名空间的二进制文件中没有CAP_SYS_ADMIN,这可能是不可能的>使用subuid和subgids与newuidmap(1)和newgidmap(1),使这些组可用(这可能会工作,但我还没有测试).>进行更改,以避免chown(2)调用失败,例如通过使用安装命名空间并将/ etc / groups中的tty组的GID更改为用户的GID.>避免chown(2)调用,例如通过使st.st_gid！= gid检查false;这可以通过从目标装载命名空间的/ etc / groups中删除tty组来实现.当然这可能会导致其他问题.