From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0FDA0C4360F for ; Thu, 4 Apr 2019 08:48:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEFA120855 for ; Thu, 4 Apr 2019 08:48:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728912AbfDDIsI (ORCPT ); Thu, 4 Apr 2019 04:48:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46558 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726563AbfDDIsH (ORCPT ); Thu, 4 Apr 2019 04:48:07 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6A10C2D80F; Thu, 4 Apr 2019 08:48:06 +0000 (UTC) Received: from carbon (ovpn-200-46.brq.redhat.com [10.40.200.46]) by smtp.corp.redhat.com (Postfix) with ESMTP id C196C62669; Thu, 4 Apr 2019 08:47:57 +0000 (UTC) Date: Thu, 4 Apr 2019 10:47:56 +0200 From: Jesper Dangaard Brouer To: Alexei Starovoitov Cc: Eric Dumazet , syzbot , Alexei Starovoitov , Daniel Borkmann , LKML , Network Development , syzkaller-bugs , brouer@redhat.com, John Fastabend , "Paul E. McKenney" Subject: Re: KASAN: use-after-free Read in __dev_map_entry_free Message-ID: <20190404104756.6b591ad6@carbon> In-Reply-To: References: <0000000000009cd09a056f1451d1@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 04 Apr 2019 08:48:06 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 3 Apr 2019 20:59:24 -0700 Alexei Starovoitov wrote: > On Tue, Apr 2, 2019 at 1:03 PM Eric Dumazet wrote: > > > > > > > > On 06/20/2018 08:19 AM, syzbot wrote: > > > Hello, > > > > > > syzbot found the following crash on: > > > > > > HEAD commit: f0dc7f9c6dd9 Merge git://git.kernel.org/pub/scm/linux/kern.. > > > git tree: bpf-next > > > console output: https://syzkaller.appspot.com/x/log.txt?x=15ad7d10400000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=fa9c20c48788d1c1 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=457d3e2ffbcf31aee5c0 > > > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > > syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1195225f800000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=171a7ce4400000 > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > Reported-by: syzbot+457d3e2ffbcf31aee5c0@syzkaller.appspotmail.com > > > > > > ================================================================== > > > BUG: KASAN: use-after-free in dev_map_flush_old kernel/bpf/devmap.c:365 [inline] > > > BUG: KASAN: use-after-free in __dev_map_entry_free+0x2a8/0x300 kernel/bpf/devmap.c:379 > > > Read of size 8 at addr ffff8801b8da38c8 by task ksoftirqd/1/18 > > > > > > CPU: 1 PID: 18 Comm: ksoftirqd/1 Not tainted 4.17.0+ #39 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > Call Trace: > > > __dump_stack lib/dump_stack.c:77 [inline] > > > dump_stack+0x1b9/0x294 lib/dump_stack.c:113 > > > print_address_description+0x6c/0x20b mm/kasan/report.c:256 > > > kasan_report_error mm/kasan/report.c:354 [inline] > > > kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412 > > > __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 > > > dev_map_flush_old kernel/bpf/devmap.c:365 [inline] > > > __dev_map_entry_free+0x2a8/0x300 kernel/bpf/devmap.c:379 > > > __rcu_reclaim kernel/rcu/rcu.h:178 [inline] > > > rcu_do_batch kernel/rcu/tree.c:2558 [inline] > > > invoke_rcu_callbacks kernel/rcu/tree.c:2818 [inline] > > > __rcu_process_callbacks kernel/rcu/tree.c:2785 [inline] > > > rcu_process_callbacks+0xe9d/0x1760 kernel/rcu/tree.c:2802 > > > __do_softirq+0x2e0/0xaf5 kernel/softirq.c:284 > > > run_ksoftirqd+0x86/0x100 kernel/softirq.c:645 > > > smpboot_thread_fn+0x417/0x870 kernel/smpboot.c:164 > > > kthread+0x345/0x410 kernel/kthread.c:240 > > > ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412 > > > > > > Allocated by task 6675: > > > save_stack+0x43/0xd0 mm/kasan/kasan.c:448 > > > set_track mm/kasan/kasan.c:460 [inline] > > > kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553 > > > kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620 > > > kmalloc include/linux/slab.h:513 [inline] > > > kzalloc include/linux/slab.h:706 [inline] > > > dev_map_alloc+0x208/0x7f0 kernel/bpf/devmap.c:102 > > > find_and_alloc_map kernel/bpf/syscall.c:129 [inline] > > > map_create+0x393/0x1010 kernel/bpf/syscall.c:453 > > > __do_sys_bpf kernel/bpf/syscall.c:2351 [inline] > > > __se_sys_bpf kernel/bpf/syscall.c:2328 [inline] > > > __x64_sys_bpf+0x303/0x510 kernel/bpf/syscall.c:2328 > > > do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:290 > > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > > > > Freed by task 26: > > > save_stack+0x43/0xd0 mm/kasan/kasan.c:448 > > > set_track mm/kasan/kasan.c:460 [inline] > > > __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521 > > > kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 > > > __cache_free mm/slab.c:3498 [inline] > > > kfree+0xd9/0x260 mm/slab.c:3813 > > > dev_map_free+0x4fa/0x670 kernel/bpf/devmap.c:191 > > > bpf_map_free_deferred+0xba/0xf0 kernel/bpf/syscall.c:262 > > > process_one_work+0xc64/0x1b70 kernel/workqueue.c:2153 > > > worker_thread+0x181/0x13a0 kernel/workqueue.c:2296 > > > kthread+0x345/0x410 kernel/kthread.c:240 > > > ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412 > > > > > > The buggy address belongs to the object at ffff8801b8da37c0 > > > which belongs to the cache kmalloc-512 of size 512 > > > The buggy address is located 264 bytes inside of > > > 512-byte region [ffff8801b8da37c0, ffff8801b8da39c0) > > > The buggy address belongs to the page: > > > page:ffffea0006e368c0 count:1 mapcount:0 mapping:ffff8801da800940 index:0xffff8801b8da3540 > > > flags: 0x2fffc0000000100(slab) > > > raw: 02fffc0000000100 ffffea0007217b88 ffffea0006e30cc8 ffff8801da800940 > > > raw: ffff8801b8da3540 ffff8801b8da3040 0000000100000004 0000000000000000 > > > page dumped because: kasan: bad access detected > > > > > > Memory state around the buggy address: > > > ffff8801b8da3780: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb > > > ffff8801b8da3800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > >> ffff8801b8da3880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > ^ > > > ffff8801b8da3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > > ffff8801b8da3980: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc > > > ================================================================== > > > > > > > > > --- > > > This bug is generated by a bot. It may contain errors. > > > See https://goo.gl/tpsmEJ for more information about syzbot. > > > syzbot engineers can be reached at syzkaller@googlegroups.com. > > > > > > syzbot will keep track of this bug report. See: > > > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with syzbot. > > > syzbot can test patches for this bug, for details see: > > > https://goo.gl/tpsmEJ#testing-patches > > > > > > What about something like : > > > > > > > > diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c > > index 191b79948424f4b21b7aa120abc03801264bf0a6..1e525d70f83354e451b738ffb8e42d83b5fa932f 100644 > > --- a/kernel/bpf/devmap.c > > +++ b/kernel/bpf/devmap.c > > @@ -164,6 +164,9 @@ static void dev_map_free(struct bpf_map *map) > > bpf_clear_redirect_map(map); > > synchronize_rcu(); > > > > + /* Make sure prior __dev_map_entry_free() have completed. */ > > + rcu_barrier(); > > + > > Eric, Thank you for looking at it. The fix makes sense to me. > > Jesper, thoughts? First I though it looked strange to have a synchronize_rcu() followed by a rcu_barrier(). But I think the fix is actually correct. We do need the rcu_barrier() call as it states "Wait until all in-flight call_rcu() callbacks complete". I wonder if we also/still need the synchronize_rcu(), but I think so as it functions as a memory-barrier across all CPUs (as in bpf_clear_redirect_map we visit all CPUs and clear any left-over per_cpu_ptr redirect_info). Acked-by: Jesper Dangaard Brouer -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer