Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754238AbcK1TEz (ORCPT ); Mon, 28 Nov 2016 14:04:55 -0500 Received: from mail-lf0-f45.google.com ([209.85.215.45]:36024 "EHLO mail-lf0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751203AbcK1TEr (ORCPT ); Mon, 28 Nov 2016 14:04:47 -0500 MIME-Version: 1.0 In-Reply-To: <1480359019.18162.79.camel@edumazet-glaptop3.roam.corp.google.com> References: <1480359019.18162.79.camel@edumazet-glaptop3.roam.corp.google.com> From: Andrey Konovalov Date: Mon, 28 Nov 2016 20:04:44 +0100 Message-ID: Subject: Re: net: GPF in eth_header To: syzkaller Cc: Hannes Frederic Sowa , Dmitry Vyukov , David Miller , Tom Herbert , Alexander Duyck , Jiri Benc , Sabrina Dubroca , netdev , LKML 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: 6385 Lines: 135 On Mon, Nov 28, 2016 at 7:50 PM, Eric Dumazet wrote: > On Sat, 2016-11-26 at 20:07 +0100, Andrey Konovalov wrote: >> On Sat, Nov 26, 2016 at 7:28 PM, 'Eric Dumazet' via syzkaller >> wrote: >> > On Sat, Nov 26, 2016 at 9:30 AM, Dmitry Vyukov wrote: >> >> Hello, >> >> >> >> The following program triggers GPF in eth_header: >> >> >> >> https://gist.githubusercontent.com/dvyukov/613cadf05543b55a419f237e419cd495/raw/5471231523d1a07c3de55f11f87472c2816ee06c/gistfile1.txt >> >> >> >> On commit 16ae16c6e5616c084168740990fc508bda6655d4 (Nov 24). >> >> >> >> BUG: unable to handle kernel paging request at ffffed002d14d74a >> >> IP: [] eth_header+0x75/0x260 net/ethernet/eth.c:88 >> >> PGD 7fff6067 [ 50.787819] PUD 7fff5067 >> >> PMD 0 [ 50.787819] >> >> Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN >> >> Modules linked in: >> >> CPU: 2 PID: 6712 Comm: a.out Not tainted 4.9.0-rc6+ #55 >> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> >> task: ffff88003a1841c0 task.stack: ffff880034d08000 >> >> RIP: 0010:[] [] >> >> eth_header+0x75/0x260 net/ethernet/eth.c:88 >> >> RSP: 0018:ffff880034d0eb68 EFLAGS: 00010a03 >> >> RAX: 1ffff1002d14d74a RBX: ffff880168a6ba4a RCX: ffff88006a9c7858 >> >> RDX: 000000000000dd86 RSI: dffffc0000000000 RDI: ffff880168a6ba56 >> >> RBP: ffff880034d0eb98 R08: 0000000000000000 R09: 0000000000000031 >> >> R10: 0000000000000002 R11: 0000000000000000 R12: 0000000000000000 >> >> R13: ffff88006c208d80 R14: 00000000000086dd R15: ffff88006a9c7858 >> >> FS: 0000000001a02940(0000) GS:ffff88006d000000(0000) knlGS:0000000000000000 >> >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> >> CR2: ffffed002d14d74a CR3: 0000000037373000 CR4: 00000000000006e0 >> >> Stack: >> >> 000000316881ab40 ffff88006a9c76c0 ffff88006881ab40 ffff88006a9c77f8 >> >> 0000000000000000 dffffc0000000000 ffff880034d0ee98 ffffffff86b31af9 >> >> ffffffff8719605c ffff880034d0f0f8 ffffffff000086dd ffffffff86be3220 >> >> Call Trace: >> >> [< inline >] dev_hard_header ./include/linux/netdevice.h:2762 >> >> [] neigh_resolve_output+0x659/0xb20 net/core/neighbour.c:1302 >> >> [< inline >] dst_neigh_output ./include/net/dst.h:464 >> >> [] ip6_finish_output2+0xb3c/0x2500 net/ipv6/ip6_output.c:121 >> >> [] ip6_finish_output+0x2eb/0x760 net/ipv6/ip6_output.c:139 >> >> [< inline >] NF_HOOK_COND ./include/linux/netfilter.h:246 >> >> [] ip6_output+0x1d7/0x9a0 net/ipv6/ip6_output.c:153 >> >> [< inline >] dst_output ./include/net/dst.h:501 >> >> [] ip6_local_out+0x9a/0x180 net/ipv6/output_core.c:170 >> >> [] ip6_send_skb+0xa6/0x340 net/ipv6/ip6_output.c:1712 >> >> [] ip6_push_pending_frames+0xb8/0xe0 >> >> net/ipv6/ip6_output.c:1732 >> >> [< inline >] rawv6_push_pending_frames net/ipv6/raw.c:607 >> >> [] rawv6_sendmsg+0x250b/0x2c20 net/ipv6/raw.c:920 >> >> [] inet_sendmsg+0x385/0x590 net/ipv4/af_inet.c:734 >> >> [< inline >] sock_sendmsg_nosec net/socket.c:621 >> >> [] sock_sendmsg+0xcf/0x110 net/socket.c:631 >> >> [] sock_write_iter+0x32b/0x620 net/socket.c:829 >> >> [] do_iter_readv_writev+0x363/0x670 fs/read_write.c:695 >> >> [] do_readv_writev+0x431/0x9b0 fs/read_write.c:872 >> >> [] vfs_writev+0x8c/0xc0 fs/read_write.c:911 >> >> [] do_writev+0x115/0x2d0 fs/read_write.c:944 >> >> [< inline >] SYSC_writev fs/read_write.c:1017 >> >> [] SyS_writev+0x2c/0x40 fs/read_write.c:1014 >> >> [] entry_SYSCALL_64_fastpath+0x23/0xc6 >> >> arch/x86/entry/entry_64.S:209 >> >> Code: 41 83 fe 04 0f 84 aa 00 00 00 e8 17 4e b0 fa 48 8d 7b 0c 48 be >> >> 00 00 00 00 00 fc ff df 44 89 f2 66 c1 c2 08 48 89 f8 48 c1 e8 03 <0f> >> >> b6 0c 30 48 8d 43 0d 49 89 c0 49 c1 e8 03 41 0f b6 34 30 49 >> >> RIP [] eth_header+0x75/0x260 net/ethernet/eth.c:88 >> >> RSP >> >> CR2: ffffed002d14d74a >> >> ---[ end trace a73fedfdc11bd60c ]--- >> > >> > >> > Hi Dmitry >> > >> > I could not reproduce the issue. Might need some specific configuration... >> > >> > loopback device has proper ethernet header (all 0) >> > >> > Fault happens in : >> > >> > 0f b6 0c 30 movzbl (%rax,%rsi,1),%ecx >> > >> > RAX=1ffff1002d14d74a which is RDI>>3, and RSI=dffffc0000000000 >> > >> > Could this be a KASAN problem ? >> >> Hi Eric, >> >> The crash happens when the kernel tries to access shadow for nonmapped memory. >> >> The issue here is an integer overflow which happens in neigh_resolve_output(). >> skb_network_offset(skb) can return negative number, but __skb_pull() >> accepts unsigned int as len. >> As a result, the least significat bit in higher 32 bits of skb->data >> gets set and we get an out-of-bounds with offset of 4 GB. >> >> I've attached a short reproducer, but you either need KASAN or to add >> a BUG_ON to see the crash. >> In this reproducer skb_network_offset() becomes negative after merging >> two ipv6 fragments. >> >> I actually see multiple places where skb_network_offset() is used as >> an argument to skb_pull(). >> So I guess every place can potentially be buggy. >> >> Thanks! > > I can not reproduce the bug on my hosts. > Quite hard to debug for me. > > skb_network_offset() can not be negative at this point, unless there is > a bug upper in the stack. Hi Eric, As far as I can see, skb_network_offset() becomes negative after pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data) in nf_ct_frag6_queue(). At least I'm able to detect that with a BUG_ON(). Also it seems that the issue is only reproducible (at least with the poc I provided) for a short time after boot. I hope that helps. > > Hannes, do you have an idea of what could be wrong in IPv6 stack ? > > Thanks. > > > -- > You received this message because you are subscribed to the Google Groups "syzkaller" group. > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller+unsubscribe@googlegroups.com. > For more options, visit https://groups.google.com/d/optout.