Manfred,
On 2015/1/23 2:15, Manfred Spraul wrote:
On 01/22/2015 03:44 AM, Ethan Zhao wrote:
On Wed, Jan 21, 2015 at 1:30 PM, Manfred Spraul
<manfred@xxxxxxxxxxxxxxxx> wrote:
On 01/21/2015 04:53 AM, Ethan Zhao wrote:
On Tue, Jan 20, 2015 at 10:10 PM, Stephen Smalley <sds@xxxxxxxxxxxxx>
wrote:
On 01/20/2015 04:18 AM, Ethan Zhao wrote:
sys_semget()
->newary()
->security_sem_alloc()
->sem_alloc_security()
selinux_sem_alloc_security()
->ipc_alloc_security() {
->rc = avc_has_perm()
if (rc) {
ipc_free_security(&sma->sem_perm);
return rc;
We free the security structure here to avoid a memory leak on a
failed/denied semaphore set creation. In this situation, we
return an
error to the caller (ultimately to newary), it does an
ipc_rcu_putref(sma, ipc_rcu_free), and it returns an error to the
caller. Thus, it never calls ipc_addid() and the semaphore set is
not
created. So how then can you call semtimedop() on it?
Seems it wouldn't happen after commit
e8577d1f0329d4842e8302e289fb2c22156abef4 ?
That was my first guess when I read the bug report - but it can't be
the
fix, because security_sem_alloc() is before the ipc_addid(), with or
without
the patch.
thread A:
thread B:
semtimedop()
-> sem_obtain_object_check()
semctl(IPC_RMID)
-> freeary()
-> ipc_rcu_putref()
-> call_rcu()
-> somehow a grace period
-> sem_rcu_free()
-> security_sem_free()
Perhaps: modify ipc_free_security() to hexdump perm and a few more
bytes if
the pointer is NULL?
I tried to ask for vmcore and do more analysis, basically, the race
condition
still exists and open a hole to be DoS.
Is the issue reproducable?
It was hit on an user's VMware while running a process named "opcmon"
maybe ported from HP_UX. I asked for the vmwcore, but not get it yet.
If yes, can you try something like the attached patch?
Yes, will.
Thanks,
Ethan
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5129,6 +5129,8 @@ static int ipc_has_perm(struct kern_ipc_perm
*ipc_perms,
u32 sid = current_sid();
isec = ipc_perms->security;
+ if (!isec)
+ return -EACCES;
ad.type = LSM_AUDIT_DATA_IPC;
ad.u.ipc_id = ipc_perms->key;
ipc_has_perm() runs without any spinlocks/semaphores, only
rcu_read_lock().
Testing for ipc_perms->security!=NULL does solve the issue that
ipc_perm->key could be an access to kfree'd memory: Nothing prevents
that the kfree could happen just after the test.
I.e.: The patch can't be the right solution.
--
Manfred
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