我们遇到了一个奇怪的问题,非root用户无法在某些目录中执行任何文件(脚本或二进制文件).本抄本说明了这个问题：
[root@b6 /]# mkdir q
[root@b6 /]# cp /bin/echo .
[root@b6 /]# cp /bin/echo q
[root@b6 /]# chown -R apps q
[root@b6 /]# ./echo ok
ok
[root@b6 /]# ./q/echo ok
ok
[root@b6 /]# su - apps
[apps@b6 ~]$cd /
[apps@b6 /]$./echo ok
ok
[apps@b6 /]$./q/echo ok
-bash: ./q/echo: Permission denied
[apps@b6 /]$ls -ld . echo q q/echo
dr-xr-xr-x. 29 root root 4096 Jun 10 00:34 .
-rwxr-xr-x. 1 root root 28176 Jun 10 00:34 echo
drwxr-xr-x. 2 apps root 4096 Jun 10 00:34 q
-rwxr-xr-x. 1 apps root 28176 Jun 10 00:34 q/echo
[apps@b6 /]# getfacl q q/echo
# file: q
# owner: apps
# group: root
user::rwx
group::r-x
other::r-x
# file: q/echo
# owner: apps
# group: root
user::rwx
group::r-x
other::r-x
[apps@b6 /]$id
uid=2070(apps) gid=2070(apps) groups=2070(apps) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
[apps@b6 /]$uname -a
Linux b6.pdc 2.6.32-358.18.1.el6.x86_64 #1 SMP Wed Aug 28 17:19:38 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
[apps@b6 /]$df / /q
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/md2 198166644 4273776 183826596 3% /
/dev/md2 198166644 4273776 183826596 3% /
[apps@b6 /]$mount
/dev/md2 on / type ext4 (rw)
...
[apps@b6 /]$getenforce
Permissive
[apps@b6 /]$strace q/echo ok
execve("q/echo",["q/echo","ok"],[/* 22 vars */]) = -1 EACCES (Permission denied)
dup(2) = 3
fcntl(3,F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
fstat(3,{st_mode=S_IFCHR|0620,st_rdev=makedev(136,0),...}) = 0
mmap(NULL,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS,-1,0) = 0x7f237b0a0000
lseek(3,SEEK_CUR) = -1 ESPIPE (Illegal seek)
write(3,"strace: exec: Permission denied\n",32strace: exec: Permission denied
) = 32
close(3) = 0
munmap(0x7f237b0a0000,4096) = 0
exit_group(1) = ?
我们的第一个想法是selinux,但这是关闭的.
接下来是f / s上的noexec,但事实并非如此.
我们的用户shell只是常规的bash(不受限制).
解决方法
我重新检查了日志(日志记录配置错误,以前拖尾邮件时没有输出 – 感谢保罗)我发现了这个：
2015-06-10T12:25:15.547452+00:00 b6 kernel: [tpe] Denied untrusted exec of /q/echo (uid:2070) by /bin/bash (uid:2070),parents: /bin/su (uid:0),/bin/bash (uid:0),/usr/sbin/sshd (uid:0),/sbin/init (deleted) (uid:0). Deny reason: directory uid not trusted
看来我们已经启用了grsecurity: Trusted Path Execution(这可能是CentOS 6.6中的默认设置),并且目录的所有者不受信任.看起来我们只需要将多个用户添加为受信任的用户,或者根据需要将其禁用.
