Re: [PATCH V2 1/1] selinux-testsuite: Add filesystem tests

[Richard Haines <richard_c_haines@btinternet.com>]

On Fri, 2020-01-10 at 13:18 -0500, Stephen Smalley wrote:
> On 1/10/20 1:09 PM, Richard Haines wrote:
> > On Thu, 2020-01-09 at 12:19 -0500, Stephen Smalley wrote:
> > > On 1/9/20 10:07 AM, Richard Haines wrote:
> > > > Test filesystem permissions and setfscreatecon(3).
> > > > 
> > > >   From kernels 5.5 filesystem { watch } is also tested.
> > > > 
> > > > Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>
> > > > ---
> > > > diff --git a/policy/test_filesystem.te
> > > > b/policy/test_filesystem.te
> > > > new file mode 100644
> > > > index 0000000..2eee1fc
> > > > --- /dev/null
> > > > +++ b/policy/test_filesystem.te
> > > > @@ -0,0 +1,324 @@
> > > > +#
> > > > +######### Test filesystem permissions policy module ##########
> > > > +#
> > > > +attribute filesystemdomain;
> > > > +
> > > > +#################### Create a test file context
> > > > ######################
> > > > +type test_filesystem_filecon_t;
> > > > +unconfined_runs_test(test_filesystem_filecon_t)
> > > > +
> > > > +################# Test all functions
> > > > ##########################
> > > > +type test_filesystem_t;
> > > > +domain_type(test_filesystem_t)
> > > > +unconfined_runs_test(test_filesystem_t)
> > > > +typeattribute test_filesystem_t testdomain;
> > > > +typeattribute test_filesystem_t filesystemdomain;
> > > > +
> > > > +allow test_filesystem_t self:capability { sys_admin };
> > > > +allow test_filesystem_t self:filesystem { mount remount
> > > > quotamod
> > > > relabelfrom relabelto unmount quotaget };
> > > > +allow test_filesystem_t self:dir { mounton add_name write };
> > > > +allow test_filesystem_t test_file_t:dir { mounton write
> > > > remove_name rmdir };
> > > > +# Create test file
> > > > +allow test_filesystem_t self:dir { add_name write };
> > > > +allow test_filesystem_t self:file { create relabelfrom
> > > > relabelto
> > > > };
> > > > +
> > > > +fs_mount_all_fs(test_filesystem_t)
> > > > +fs_remount_all_fs(test_filesystem_t)
> > > > +fs_unmount_all_fs(test_filesystem_t)
> > > > +fs_relabelfrom_all_fs(test_filesystem_t)
> > > > +fs_get_xattr_fs_quotas(test_filesystem_t)
> > > > +files_search_all(test_filesystem_t)
> > > > +# Required for mount opts
> > > > "rootcontext=system_u:object_r:test_filesystem_t:s0";
> > > > +fs_associate(test_filesystem_t)
> > > > +fs_getattr_xattr_fs(test_filesystem_t)
> > > > +
> > > > +# For running quotacheck(8)
> > > > +files_type(test_filesystem_t)
> > > > +# Update quotas
> > > > +fs_set_all_quotas(test_filesystem_t)
> > > > +allow test_filesystem_t self:file { quotaon };
> > > > +# Create test file and change context:
> > > > +fs_associate(test_filesystem_filecon_t)
> > > > +allow test_filesystem_t test_filesystem_filecon_t:file { open
> > > > read
> > > > getattr relabelto write };
> > > > +dontaudit test_filesystem_t kernel_t:process { setsched };
> > > 
> > > Why do you need these dontaudit statements?  It seems like a
> > > kernel
> > > bug
> > > if something is triggering a setsched permission check on the
> > > kernel_t
> > > domain?  Something the kernel module is doing during
> > > initialization?
> > > 
> > 
> > I've tracked this down to them all being called from block/ioprio.c
> > with: security_task_setioprio(task, ioprio) ->
> > selinux_task_setioprio
> > 
> > Why the SECCLASS_PROCESS, PROCESS__SETSCHED I've no idea. The
> > following
> > also use SET/GETSCHED permission:
> > 
> > selinux_task_getioprio, selinux_task_setnice,
> > selinux_task_movememory
> 
> The confusing bit is that it is between test_filesystem_t and
> kernel_t. 
> If the process was setting its own ioprio, then I'd expect to see
> the 
> denial between test_filesystem_t and test_filesystem_t aka self.  If
> the 
> process inserted a kernel module and the module initializer spawned
> a 
> kernel thread that set its ioprio, I would expect it to be kernel_t
> to 
> kernel_t.

Some more info on who calls set_task_ioprio:

fs/ext4/super.c calls 'set_task_ioprio' in two places using:
    set_task_ioprio(sbi->s_journal->j_task, journal_ioprio);
The return codes are not checked. This code was added 11 years ago.

fs/btrfs/reada.c also calls 'set_task_ioprio' in two places using:
    set_task_ioprio(current, BTRFS_IOPRIO_READA);
The return codes are not checked.

As can be seen the ext4 module does not use 'current'. I have patched
kernel 5.5-rc5 to use 'current' and it now works as you expected. Also
the kernel_t:process { setsched } rules can be removed.
As the problem will exist for some time, I've added to the test policy:
    kernel_dontaudit_setsched(filesystemdomain)

It appears that most of the refpolicy modules do the same.