Re: question about selinux_restore_tty() in sudo's selinux.c

[Dominick Grift <dac.override@gmail.com>]

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On Fri, Sep 27, 2019 at 09:51:26AM -0400, Stephen Smalley wrote:
> On 9/27/19 9:49 AM, Dominick Grift wrote:
> > On Fri, Sep 27, 2019 at 09:33:06AM -0400, Stephen Smalley wrote:
> > > On 9/27/19 9:08 AM, Dominick Grift wrote:
> > > > On Fri, Sep 27, 2019 at 08:59:26AM -0400, Stephen Smalley wrote:
> > > > > On 9/27/19 3:55 AM, Dominick Grift wrote:
> > > > > > sudo does not reset the role of my tty properly [1], and i was wondering if anyone is able to determine what is causing this [2]
> > > > > > 
> > > > > > [1] https://bugzilla.sudo.ws/show_bug.cgi?id=898
> > > > > > [2] https://www.sudo.ws/repos/sudo/file/tip/src/selinux.c
> > > > > 
> > > > > Are you sure sudo is calling selinux_restore_tty()?
> > > > > 
> > > > > 
> > > > 
> > > > running sudo with:
> > > > 
> > > > Debug sudo /var/log/sudo_debug all@debug
> > > > Debug sudoers.so /var/log/sudo_debug all@debug
> > > > 
> > > > Yields:
> > > > 
> > > > grep selinux /var/log/sudo_debug
> > > > Sep 27 15:06:29 sudo[3417] <- sudo_new_key_val_v1 @ ../../../lib/util/key_val.c:61 := selinux_role=sysadm.role
> > > > Sep 27 15:06:29 sudo[3417]     7: selinux_role=sysadm.role
> > > > Sep 27 15:06:29 sudo[3447] -> selinux_setup @ ../../src/selinux.c:349
> > > > Sep 27 15:06:29 sudo[3447] -> get_exec_context @ ../../src/selinux.c:274
> > > > Sep 27 15:06:29 sudo[3447] <- get_exec_context @ ../../src/selinux.c:328 := 0x564eed3621b0
> > > > Sep 27 15:06:29 sudo[3447] -> relabel_tty @ ../../src/selinux.c:160
> > > > Sep 27 15:06:29 sudo[3447] <- relabel_tty @ ../../src/selinux.c:253 := 0
> > > > Sep 27 15:06:29 sudo[3447] -> audit_role_change @ ../../src/selinux.c:76
> > > > Sep 27 15:06:29 sudo[3447] <- audit_role_change @ ../../src/selinux.c:98 := 6
> > > > Sep 27 15:06:29 sudo[3447] <- selinux_setup @ ../../src/selinux.c:395 := 0
> > > > Sep 27 15:06:29 sudo[3447] -> selinux_execve @ ../../src/selinux.c:405
> > > > Sep 27 15:06:29 sudo[3417] -> selinux_restore_tty @ ../../src/selinux.c:114
> > > > Sep 27 15:06:29 sudo[3417] <- selinux_restore_tty @ ../../src/selinux.c:142 := 0
> > > 
> > > Ok, so you entered and exited selinux_restore_tty() without error. No
> > > warning messages of any kind in any of the sudo logs? Not sure where
> > > sudo_warn() and sudo_warnx() messages go.
> > 
> > No warnings or any other clues. I guess it must be this then:
> > 
> >      if (se_state.ttyfd == -1 || se_state.new_tty_context == NULL)
> > 	goto skip_relabel;
> 
> That should only occur if there was no tty or security_compute_relabel()
> didn't provide a new context to set in the first place. Not if it actually
> relabeled the tty earlier.
> 
> Does newrole work correctly with your policy?

Yes:

kcinimod@seamus:~$ id -Z
wheel.id:wheel.role:wheel.subj:s0
kcinimod@seamus:~$ ls -alZ `tty`
crw--w----. 1 kcinimod tty wheel.id:wheel.role:users.terminals.pty.pty_file:s0 136, 10 Sep 27 15:55 /dev/pts/10
kcinimod@seamus:~$ newrole -r sysadm.role
Password: 
newrole: incorrect password for kcinimod
kcinimod@seamus:~$ ls -alZ `tty`
crw--w----. 1 kcinimod tty wheel.id:wheel.role:users.terminals.pty.pty_file:s0 136, 10 Sep 27 15:56 /dev/pts/10
kcinimod@seamus:~$ newrole -r sysadm.role
Password: 
kcinimod@seamus:~$ id -Z
wheel.id:sysadm.role:sysadm.subj:s0
kcinimod@seamus:~$ ls -alZ `tty`
crw--w----. 1 kcinimod tty wheel.id:sysadm.role:users.terminals.pty.pty_file:s0 136, 10 Sep 27 15:56 /dev/pts/10
kcinimod@seamus:~$ exit
logout
kcinimod@seamus:~$ ls -alZ `tty`
crw--w----. 1 kcinimod tty wheel.id:wheel.role:users.terminals.pty.pty_file:s0 136, 10 Sep 27 15:56 /dev/pts/10

> 
> > 
> > > 
> > > selinux_restore_tty() does a goto skip_relabel in multiple cases:
> > > - if there was no tty (ttyfd == -1),
> > > - if we didn't set a new tty context (new_tty_context),
> > > - if the context on the tty was changed from the value set by sudo
> > > (strcmp...) e.g. some other process changed it in the interim, but this
> > > should have logged a warning,
> > > 
> 
> 

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Dominick Grift

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