On Sat, Dec 23, 2017 at 3:03 AM, Li Kun <hw.likun@xxxxxxxxxx> wrote:
Hi all,
When i start a docker container, the runc will call selinux_setprocattr to set the exec_sid before start the container.
Meanwhile if i use "semodule -i" to load a policy pp, the old sidtab will be shutdown before switch to the new sidtab, and cause
sidtab_context_to_sid failed with the errno -NOMEM.
Error message:
Dec 14 09:18:18 wuwenming_vudfua_0 docker: time="2017-12-14T09:18:18.549862564+08:00" level=error msg="Handler for GET /v1.23/containers/192.168.0.2: 9082/dfs_d: returned error: No such container: 192.168.0.2:9082/dfs_d:V100R013C11SPC000BCD2/json V100R013C11SPC000BCD2 "
Dec 14 09:18:18 wuwenming_vudfua_0 kernel: [ 48.463179] SELinux: security_context_to_sid(system_u:object_r:svirt_ sandbox_file_t:s0:c290,c371) failed for (dev overlay, type overlay) errno=-12
Dec 14 09:18:18 wuwenming_vudfua_0 dbus-daemon: dbus[720]: avc: received policyload notice (seqno=2)
Dec 14 09:18:18 wuwenming_vudfua_0 dbus[720]: avc: received policyload notice (seqno=2)
runcsemodule
->selinux_setprocattr->security_load_policy
->security_context_to_sid ->sidtab_shutdown(oldsidtab)
->read_lock(&policy_rwlock);->sidtab_map(&oldsidtab, clone_sid, &newsidtab);
->sidtab_context_to_sid
{
....
if (s->next_sid == UINT_MAX || s->shutdown) {
ret = -ENOMEM;
....
}
->read_unlock(&policy_rwlock);
->write_lock_irq(&policy_rwlock);
->"switch to new policydb"
->write_unlock_irq(&policy_rwlock);
I wonder that if this is the intention or a bug?
If it is the intention, what should the application do when it get -ENOMEM error, to try again?
If it is a bug, may the two options below suitable to solve the issue?
Option1:
use policy_rwlock to protect the "sidtab_shutdown" & "sidtab_map" , load_policy is rarely to be called after system bringing up,
so i think it will not impact much on the performance.
Option2:
Use a temp list to store the sid in oldsidtab after it is shutdown, and deal with it
after cloning the major sids from oldsidtab to newsidtab and getting the policy_rwlock.
The current logic is intentional. One might argue that a different error code might be more suitable in this situation (e.g. EAGAIN or something), but ENOMEM is already a possible error code when loading policy upon transient OOM conditions, so the caller might have to retry regardless. The policy write lock must only be held for the minimal critical section as otherwise all system activity could be blocked; it is only held when making the new policydb and sidtab active not during their allocation and setup - ideally it would be further reduced to a couple of pointer updates. Is this scenario something you are encountering in actual practice or just a theoretically possible one?
