Hi,
On 01/20/2015 03:10 PM, Stephen Smalley wrote:
On 01/20/2015 04:18 AM, Ethan Zhao wrote:
A NULL pointer dereference was observed as following panic:
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff812735eb>] ipc_has_perm+0x4b/0x60
...
Process opcmon (pid: 30712, threadinfo ffff880237f2a000,
task ffff88022ac70e40)
Stack:
ffff880237f2bc04 ffffffff01020953 ffff880237f2bce8
ffffffff8125818e
0000000000000001 0000000037f78004 ffff880237f2bcd8
ffffffff81273619
ffff880237f2bce8 ffffffff8126e3e6 ffff880237f2bf68
ffffffff8125c206
Call Trace:
[<ffffffff8125818e>] ? ipcperms+0xae/0x110
[<ffffffff81273619>] selinux_sem_semop+0x19/0x20
[<ffffffff8126e3e6>] security_sem_semop+0x16/0x20
[<ffffffff8125c206>] sys_semtimedop+0x346/0x750
[<ffffffff81188c0c>] ? handle_pte_fault+0x1dc/0x200
[<ffffffff8161d830>] ? __do_page_fault+0x280/0x500
[<ffffffff810d97d0>] ? __lock_release+0x90/0x1b0
[<ffffffff8161d830>] ? __do_page_fault+0x280/0x500
[<ffffffff8109a763>] ? up_read+0x23/0x40
[<ffffffff8161d830>] ? __do_page_fault+0x280/0x500
[<ffffffff81182f1c>] ? might_fault+0x5c/0xb0
[<ffffffff81081f96>] ? sys_newuname+0x66/0xf0
[<ffffffff810d97d0>] ? __lock_release+0x90/0x1b0
[<ffffffff81081f96>] ? sys_newuname+0x66/0xf0
[<ffffffff81622f45>] ? sysret_check+0x22/0x5d
[<ffffffff8125c620>] sys_semop+0x10/0x20
[<ffffffff81622f19>] system_call_fastpath+0x16/0x1b
Code: b8 00 00 48 8b 80 48 06 00 00 41 8b 54 24 40 4c 8d
45 d0 89 d9 45 31 c9 48 8b 40 70 8b 78 04 49 8b 44 24 60 c6 45 d0 04 89 55 d8
<0f> b7 10 8b 70 04 e8 0a dc ff ff 48 83 c4 20 5b 41 5c c9 c3 90
RIP [<ffffffff812735eb>] ipc_has_perm+0x4b/0x60
RSP <ffff880237f2bc98>
CR2: 0000000000000000
The root cause is semtimedop() was called after semget() without checking its
return value in process opcmon. and semget() failed to check permission in
function avc_has_perm() then sem_perm->security was freed shown as following:
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?
My only idea would be a race of semtimedop() with IPC_RMID:
If a rcu grace period happens between sem_obtain_object_check() and the
ipc_has_perm() call, the the observed NULL pointer assignment would happen.
So ipc_perms->security was NULL, then semtimedop() was called as
following:
sys_semtimedop() / semop()
->selinux_sem_semop()
->ipc_has_perm()
->avc_has_perm(sid, isec->sid, isec->sclass, perms, &ad);
^- NULL pointer dereference happens
The test kernel was running on VMware.
Can you give some more details?
- which RCU type?
- PREEMPT?
--
Manfred
_______________________________________________
Selinux mailing list
Selinux@xxxxxxxxxxxxx
To unsubscribe, send email to Selinux-leave@xxxxxxxxxxxxx.
To get help, send an email containing "help" to Selinux-request@xxxxxxxxxxxxx.
