1 |
Hi, |
2 |
|
3 |
I have been wrestling with a problem for some time and I cannot see what |
4 |
I am doing wrong. Here is an outline: |
5 |
|
6 |
AIM - to be able to su to root and switch off strict mode in case |
7 |
something goes wrong. I was using newrole but I kept forgetting so I am |
8 |
trying to use pam_selinux to change the role to sysadm_r. I followed the |
9 |
instructions given at |
10 |
http://blog.siphos.be/2013/04/how-logins-get-their-selinux-user-context/ |
11 |
in general, but I had to do some research to find out how to apply them |
12 |
for /bin/su. |
13 |
|
14 |
The answer was in su.if, added to the "su_role_template" interface. I |
15 |
then spent some time figuring out how to get the roles/sysadm module to |
16 |
use my modified interface (put it in the same directory) and it |
17 |
generally seemed to work. I got a few extra AVCs but I ended up with the |
18 |
following: |
19 |
|
20 |
optional_policy(` |
21 |
domain_subj_id_change_exemption($1_su_t) |
22 |
domain_role_change_exemption($1_su_t) |
23 |
|
24 |
selinux_validate_context($1_su_t) |
25 |
selinux_compute_access_vector($1_su_t) |
26 |
selinux_compute_create_context($1_su_t) |
27 |
selinux_compute_relabel_context($1_su_t) |
28 |
selinux_compute_user_contexts($1_su_t) |
29 |
|
30 |
seutil_read_config($1_su_t) |
31 |
seutil_read_default_contexts($1_su_t) |
32 |
|
33 |
userdom_relabelto_user_ptys($1_su_t) |
34 |
userdom_dontaudit_relabelfrom_user_ptys($1_su_t) |
35 |
userdom_use_user_ptys($1_su_t) |
36 |
allow $1_su_t self:process setkeycreate; |
37 |
allow $1_su_t $3:key manage_key_perms; |
38 |
') |
39 |
|
40 |
The PROBLEM: I still get two AVCs that I don't think I should be getting: |
41 |
|
42 |
type=PROCTITLE msg=audit(1485020695.038:10367): |
43 |
proctitle=2F62696E2F7375002D |
44 |
type=PATH msg=audit(1485020695.038:10367): item=0 name="/dev/pts/3" |
45 |
inode=6 dev=00:12 mode=020620 ouid=501 ogid=5 rdev=88:03 |
46 |
obj=staff_u:object_r:user_devpts_t nametype=NORMAL |
47 |
type=CWD msg=audit(1485020695.038:10367): |
48 |
cwd="/home/robert/selinux/sysadm" |
49 |
type=SYSCALL msg=audit(1485020695.038:10367): arch=c000003e |
50 |
syscall=188 success=yes exit=0 a0=375183c820 a1=3817fb1fcaa |
51 |
a2=375183bce0 a3=1c items=1 ppid=17744 pid=20374 |
52 |
auid=4294967295 uid=501 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 |
53 |
fsgid=0 tty=pts3 |
54 |
ses=4294967295 comm="su" exe="/bin/su" |
55 |
subj=staff_u:sysadm_r:sysadm_su_t key=(null) |
56 |
type=AVC msg=audit(1485020695.038:10367): avc: denied { relabelto |
57 |
} for pid=20374 comm="su" name="3" dev="devpts" ino=6 |
58 |
scontext=staff_u:sysadm_r:sysadm_su_t |
59 |
tcontext=root:object_r:user_devpts_t tclass=chr_file permissive=1 |
60 |
---- |
61 |
type=AVC msg=audit(1485020695.038:10368): avc: denied { create } |
62 |
for pid=20374 comm="su" scontext=staff_u:sysadm_r:sysadm_su_t |
63 |
tcontext=root:sysadm_r:sysadm_t tclass=key permissive=1 |
64 |
|
65 |
I double checked that I had corresponding rules to allow these: |
66 |
|
67 |
# sesearch -s sysadm_su_t -t user_devpts_t -A |
68 |
allow sysadm_su_t user_devpts_t:chr_file { read getattr write ioctl |
69 |
relabelto open append }; |
70 |
|
71 |
# sesearch -s sysadm_su_t -t sysadm_t -c key -A |
72 |
allow sysadm_su_t sysadm_t:key { search setattr read create write |
73 |
link view }; |
74 |
|
75 |
So I really cannot see why I am getting these AVCs. I keep looking at |
76 |
the scripts, the rules and the AVCs to see if I have done something |
77 |
stupid, but I cannot see it. I have started making fairly arbitrary |
78 |
changes to see if I can make it go away but I am just wasting time |
79 |
really. If I cannot figure this out I suspect I will be ditching |
80 |
pam_selinux and reverting to explicitly issuing newrole. I guess with |
81 |
strict on I will quickly be reminded that I have forgotten to change |
82 |
roles anyway. |
83 |
|
84 |
Thanks in advance, |
85 |
|
86 |
Robert Sharp |