From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from szxga04-in.huawei.com ([45.249.212.190]:4008 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752224AbdHPN3J (ORCPT ); Wed, 16 Aug 2017 09:29:09 -0400 Message-ID: <59944642.6050005@huawei.com> Date: Wed, 16 Aug 2017 21:18:58 +0800 From: zhong jiang MIME-Version: 1.0 To: zhong jiang CC: , , , , , , , , Subject: Re: [PATCH] mm/mempolicy: fix use after free when calling get_mempolicy References: <1502849621-12420-1-git-send-email-zhongjiang@huawei.com> In-Reply-To: <1502849621-12420-1-git-send-email-zhongjiang@huawei.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: + stable@vger.kernel.org On 2017/8/16 10:13, zhong jiang wrote: > I hit an use after free issue by executing trinity. and repoduce it > with KASAN enabled. The related call trace is as follows. > > BUG: KASan: use after free in SyS_get_mempolicy+0x3c8/0x960 at addr ffff8801f582d766 > Read of size 2 by task syz-executor1/798 > > INFO: Allocated in mpol_new.part.2+0x74/0x160 age=3 cpu=1 pid=799 > __slab_alloc+0x768/0x970 > kmem_cache_alloc+0x2e7/0x450 > mpol_new.part.2+0x74/0x160 > mpol_new+0x66/0x80 > SyS_mbind+0x267/0x9f0 > system_call_fastpath+0x16/0x1b > INFO: Freed in __mpol_put+0x2b/0x40 age=4 cpu=1 pid=799 > __slab_free+0x495/0x8e0 > kmem_cache_free+0x2f3/0x4c0 > __mpol_put+0x2b/0x40 > SyS_mbind+0x383/0x9f0 > system_call_fastpath+0x16/0x1b > INFO: Slab 0xffffea0009cb8dc0 objects=23 used=8 fp=0xffff8801f582de40 flags=0x200000000004080 > INFO: Object 0xffff8801f582d760 @offset=5984 fp=0xffff8801f582d600 > > Bytes b4 ffff8801f582d750: ae 01 ff ff 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ > Object ffff8801f582d760: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk > Object ffff8801f582d770: 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkk. > Redzone ffff8801f582d778: bb bb bb bb bb bb bb bb ........ > Padding ffff8801f582d8b8: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ > Memory state around the buggy address: > ffff8801f582d600: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff8801f582d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ffff8801f582d700: fc fc fc fc fc fc fc fc fc fc fc fc fb fb fb fc > when calling get_mempolicy from userspace, it only hold the mmap_sem > and increase the shared pol count, the unshared pol is not be increased. > it premature release the mmap_sem, it will result in the related mempolicy > maybe had freed by mbind. then, the issue will trigger. > > The patch fix the issue by removing the premature release. it will safe > access the mempolicy. The issue will leave. > > Signed-off-by: zhong jiang > --- > mm/mempolicy.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index d911fa5..618ab12 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -861,11 +861,6 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, > *policy |= (pol->flags & MPOL_MODE_FLAGS); > } > > - if (vma) { > - up_read(¤t->mm->mmap_sem); > - vma = NULL; > - } > - > err = 0; > if (nmask) { > if (mpol_store_user_nodemask(pol)) {