Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754767AbdDEBLn (ORCPT ); Tue, 4 Apr 2017 21:11:43 -0400 Received: from mail-wr0-f193.google.com ([209.85.128.193]:33444 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752634AbdDEBLk (ORCPT ); Tue, 4 Apr 2017 21:11:40 -0400 MIME-Version: 1.0 In-Reply-To: References: From: Cong Wang Date: Tue, 4 Apr 2017 18:11:18 -0700 Message-ID: Subject: Re: net/ipv4: use-after-free in ipv4_mtu To: Eric Dumazet Cc: Andrey Konovalov , "David S. Miller" , netdev , LKML , Dmitry Vyukov , Kostya Serebryany , syzkaller Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5596 Lines: 126 On Tue, Apr 4, 2017 at 11:51 AM, Eric Dumazet wrote: > On Tue, Apr 4, 2017 at 7:50 AM, Andrey Konovalov wrote: >> >> Hi, >> >> I've got the following error report while fuzzing the kernel with syzkaller. >> >> On commit a71c9a1c779f2499fb2afc0553e543f18aff6edf (4.11-rc5). >> >> Unfortunately it's not reproducible. >> >> ================================================================== >> BUG: KASAN: use-after-free in dst_metric_raw include/net/dst.h:176 >> [inline] at addr ffff88003d6a965c >> BUG: KASAN: use-after-free in ipv4_mtu+0x3f2/0x4b0 >> net/ipv4/route.c:1270 at addr ffff88003d6a965c >> Read of size 4 by task syz-executor3/20611 >> CPU: 3 PID: 20611 Comm: syz-executor3 Not tainted 4.11.0-rc5+ #199 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> Call Trace: >> __dump_stack lib/dump_stack.c:16 [inline] >> dump_stack+0x292/0x398 lib/dump_stack.c:52 >> kasan_object_err+0x1c/0x70 mm/kasan/report.c:164 >> print_address_description mm/kasan/report.c:202 [inline] >> kasan_report_error mm/kasan/report.c:291 [inline] >> kasan_report+0x252/0x510 mm/kasan/report.c:347 >> __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:367 >> dst_metric_raw include/net/dst.h:176 [inline] >> ipv4_mtu+0x3f2/0x4b0 net/ipv4/route.c:1270 >> dst_mtu include/net/dst.h:221 [inline] >> do_ip_getsockopt+0x71d/0x2290 net/ipv4/ip_sockglue.c:1433 >> ip_getsockopt+0x90/0x230 net/ipv4/ip_sockglue.c:1578 >> tcp_getsockopt+0x82/0xd0 net/ipv4/tcp.c:3131 >> sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2709 >> SYSC_getsockopt net/socket.c:1829 [inline] >> SyS_getsockopt+0x252/0x390 net/socket.c:1811 >> entry_SYSCALL_64_fastpath+0x1f/0xc2 >> RIP: 0033:0x4458d9 >> RSP: 002b:00007fe87f452b58 EFLAGS: 00000286 ORIG_RAX: 0000000000000037 >> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00000000004458d9 >> RDX: 000000000000000e RSI: 0000000000000000 RDI: 0000000000000005 >> RBP: 00000000006e0020 R08: 0000000020db6000 R09: 0000000000000000 >> R10: 00000000207e8000 R11: 0000000000000286 R12: 0000000000708150 >> R13: 0000000020db8000 R14: 0000000000001000 R15: 0000000000000003 >> Object at ffff88003d6a9658, in cache kmalloc-64 size: 64 >> Allocated: >> PID = 20110 >> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 >> save_stack+0x43/0xd0 mm/kasan/kasan.c:513 >> set_track mm/kasan/kasan.c:525 [inline] >> kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616 >> kmem_cache_alloc_trace+0x82/0x270 mm/slub.c:2745 >> kmalloc include/linux/slab.h:490 [inline] >> kzalloc include/linux/slab.h:663 [inline] >> fib_create_info+0x8e0/0x3a30 net/ipv4/fib_semantics.c:1040 >> fib_table_insert+0x1a5/0x1550 net/ipv4/fib_trie.c:1221 >> ip_rt_ioctl+0xddc/0x1590 net/ipv4/fib_frontend.c:597 >> inet_ioctl+0xf2/0x1c0 net/ipv4/af_inet.c:882 >> sctp: [Deprecated]: syz-executor0 (pid 20638) Use of int in max_burst >> socket option. >> Use struct sctp_assoc_value instead >> sock_do_ioctl+0x65/0xb0 net/socket.c:906 >> sock_ioctl+0x28f/0x440 net/socket.c:1004 >> vfs_ioctl fs/ioctl.c:45 [inline] >> do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:685 >> SYSC_ioctl fs/ioctl.c:700 [inline] >> SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 >> entry_SYSCALL_64_fastpath+0x1f/0xc2 >> Freed: >> PID = 4439 >> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 >> save_stack+0x43/0xd0 mm/kasan/kasan.c:513 >> set_track mm/kasan/kasan.c:525 [inline] >> kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:589 >> slab_free_hook mm/slub.c:1357 [inline] >> slab_free_freelist_hook mm/slub.c:1379 [inline] >> slab_free mm/slub.c:2961 [inline] >> kfree+0xe8/0x2b0 mm/slub.c:3882 >> free_fib_info_rcu+0x4ba/0x5e0 net/ipv4/fib_semantics.c:218 >> __rcu_reclaim kernel/rcu/rcu.h:118 [inline] >> rcu_do_batch.isra.64+0x947/0xcc0 kernel/rcu/tree.c:2879 >> invoke_rcu_callbacks kernel/rcu/tree.c:3142 [inline] >> __rcu_process_callbacks kernel/rcu/tree.c:3109 [inline] >> rcu_process_callbacks+0x2cc/0xb90 kernel/rcu/tree.c:3126 >> __do_softirq+0x2fb/0xb7d kernel/softirq.c:284 >> Memory state around the buggy address: >> ffff88003d6a9500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ffff88003d6a9580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> >ffff88003d6a9600: fc fc fc fc fc fc fc fc fc fc fc fb fb fb fb fb >> ^ >> ffff88003d6a9680: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc >> ffff88003d6a9700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ================================================================== > > Thanks for the report Andrey > > Looking at fib->fib_metrics, I fail to understand how the following can work : > > dst_init_metrics(&rt->dst, fi->fib_metrics, true); > > In the cases fi->fib_metrics is _not_ dst_default_metrics, > fi->fib_metrics can be freed when the fib is deleted, > while dst(s) have still the 'read only pointer'. > > RCU grace period before fi->fib_metrics freeing does not help. > > Without refcounts, it looks like we need to copy the fib_metrics. The dst is obtained from sk_dst_cache which is cached for a fast path where fib_info is obtained in fib_lookup() without refcnt: err = fib_table_lookup(tb, flp, res, flags | FIB_LOOKUP_NOREF); ... if (!(fib_flags & FIB_LOOKUP_NOREF)) atomic_inc(&fi->fib_clntref); This probably starts from: commit ebc0ffae5dfb4447e0a431ffe7fe1d467c48bbb9 Author: Eric Dumazet Date: Tue Oct 5 10:41:36 2010 +0000 fib: RCU conversion of fib_lookup()