linux - chown 不设置 SGID

Question

我正在尝试创建一个权限为 02770 的目录，这样生成的权限将是 drwxrws---

当我运行以下命令时，我得到了预期的行为

rsam.svtest2.serendipity> (/home/svtest2)
$ mkdir abc


rsam.svtest2.serendipity> (/home/svtest2)
$ ls -lrt
drwxrwxr-x  2 svtest2 users    6 Apr 18 10:57 abc

rsam.svtest2.serendipity> (/home/svtest2)
$ chmod 02770 abc

rsam.svtest2.serendipity> (/home/svtest2)
$ ls -lrt
drwxrws---  2 svtest2 users    6 Apr 18 10:57 abc

更新#1从上面开始，在目录上运行 mkdir 和 chmod 之后，当我运行 chown 时，SGID 位被清除。

rsam.svtest2.serendipity> (/home/svtest2)
$ chown svtest2:users abc



rsam.svtest2.serendipity> (/home/svtest2)
$ ls -lrt
drwxrwx---  2 svtest2 users    6 Apr 18 10:57 abc

来自chown documentation ,

Only a privileged process (Linux: one with the CAP_CHOWN capability) may change the owner of a file. The owner of a file may change the group of the file to any group of which that owner is a member. A privileged process (Linux: with CAP_CHOWN) may change the group arbitrarily.

问题是我的用户 svtest 没有 CAP_CHOWN 能力。现在问题归结为 - 如何让用户拥有 CAP_CHOWN 功能？

看起来这里有一些说明 - SO - setting CAP_CHOWN但我还没有尝试过。

但是，当我在 C++ 代码(燕尾服服务器的一部分)下运行时

// Check if the directory exists and if not creates the directory
// with the given permissions.
struct stat st;
int lreturn_code = stat(l_string, &st);



if (lreturn_code != 0 &&
    (mkdir(l_string, lpermission) != 0 ||
     chmod(l_string, lpermission) != 0)) {
     ....
     ....
     }
     ....
     ....
// Convert group name to group id into lgroup
        if (chown(l_string, -1, lgroup) != 0) {
            // System error.
        }

目录创建如下:

$ ls -l|grep DirLevel1
drwxrwx--- 2 svtest2 users         6 Apr 18 11:14 DirLevel1

请注意，与如上所述直接运行命令时相比，SGUID 位未设置。

操作的strace摘录:

5864  stat("/home/svtest2/data/server/log/DirLevel1/", 0x7ffd235f29f0) = -1       ENOENT (No such file or directory)
5864  mkdir("/home/svtest2/data/server/log/DirLevel1/", 02770) = 0
5864  chmod("/home/svtest2/data/server/log/DirLevel1/", 02770) = 0
5864  socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 15
5864  connect(15, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
5864  close(15)                         = 0
5864  socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 15
5864  connect(15, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"},  110) = -1 ENOENT (No such file or directory)
5864  close(15)                         = 0
5864  open("/etc/group", O_RDONLY|O_CLOEXEC) = 15
5864  fstat(15, {st_mode=S_IFREG|0644, st_size=652, ...}) = 0
5864  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f414d7c4000
5864  read(15, "root:x:0:\nbin:x:1:\ndaemon:x:2:\ns"..., 4096) = 652
5864  close(15)                         = 0
5864  munmap(0x7f414d7c4000, 4096)      = 0
5864  chown("/home/svtest2/data/server/log/DirLevel1/", 4294967295, 100) = 0
5864  write(7, "\0\0\2~\6\0\0\0\0\0\21i\216\376\377\377\377\377\377\377\377\1\0\0\0\0\0\0\0\1\0\0"..., 638) = 638
5864  read(7, "\0\0\0\300\6\0\0\0\0\0\10\0\0\0\0\250\0\0\0\0\0\0\0\0\0(\0\0\0\0\0\0"..., 8208) = 192
5864  write(7, "\0\0\1}\6\0\0\0\0\0\3h\221\1\0\0\0\0\0\0\0\376\377\377\377\377\377\377\377\250\0\0"..., 381) = 381
5864  read(7, "\0\0\0\26\6\0\0\0\0\0\10\4\0\0\0\t\1\0\0\0\215\f", 8208) = 22
5864  msgsnd(43679799, {805306373, "y\0\0\0007\200\232\2\0\0\0\0\f\2\0\0\0\0\0\200\0\0\0\0\0\0\0\0\0\0\0\0"...}, 516, IPC_NOWAIT) = 0
5864  msgrcv(43614264,

来自 http://man.sourcentral.org/RHEL7/2+chown ,

When the owner or group of an executable file are changed by an unprivileged user the S_ISUID and S_ISGID mode bits are cleared. POSIX does not specify whether this also should happen when root does the chown(); the Linux behavior depends on the kernel version. In case of a non-group-executable file (i.e., one for which the S_IXGRP bit is not set) the S_ISGID bit indicates mandatory locking, and is not cleared by a chown().

上面突出显示了一种可能的情况，但我不确定它如何适用于我的情况，因为它不是可执行文件而是一个目录。

Answer 1

由于 *nix 系统通过查看“x”权限位将文件视为可执行文件，我相信可搜索目录也可能被视为可执行文件。