On Mon, Nov 28, 2016 at 8:04 PM, 'Andrey Konovalov' via syzkaller <syzkal...@googlegroups.com> wrote: > On Mon, Nov 28, 2016 at 7:50 PM, Eric Dumazet <eric.duma...@gmail.com> 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 >>> <syzkal...@googlegroups.com> wrote: >>> > On Sat, Nov 26, 2016 at 9:30 AM, Dmitry Vyukov <dvyu...@google.com> 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: [<ffffffff86be3295>] 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:[<ffffffff86be3295>] [<ffffffff86be3295>] >>> >> 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 >>> >> [<ffffffff86b31af9>] neigh_resolve_output+0x659/0xb20 >>> >> net/core/neighbour.c:1302 >>> >> [< inline >] dst_neigh_output ./include/net/dst.h:464 >>> >> [<ffffffff8719605c>] ip6_finish_output2+0xb3c/0x2500 >>> >> net/ipv6/ip6_output.c:121 >>> >> [<ffffffff871a0b0b>] ip6_finish_output+0x2eb/0x760 >>> >> net/ipv6/ip6_output.c:139 >>> >> [< inline >] NF_HOOK_COND ./include/linux/netfilter.h:246 >>> >> [<ffffffff871a1157>] ip6_output+0x1d7/0x9a0 net/ipv6/ip6_output.c:153 >>> >> [< inline >] dst_output ./include/net/dst.h:501 >>> >> [<ffffffff873312ea>] ip6_local_out+0x9a/0x180 net/ipv6/output_core.c:170 >>> >> [<ffffffff871a3886>] ip6_send_skb+0xa6/0x340 net/ipv6/ip6_output.c:1712 >>> >> [<ffffffff871a3bd8>] ip6_push_pending_frames+0xb8/0xe0 >>> >> net/ipv6/ip6_output.c:1732 >>> >> [< inline >] rawv6_push_pending_frames net/ipv6/raw.c:607 >>> >> [<ffffffff8722acfb>] rawv6_sendmsg+0x250b/0x2c20 net/ipv6/raw.c:920 >>> >> [<ffffffff8701c4f5>] inet_sendmsg+0x385/0x590 net/ipv4/af_inet.c:734 >>> >> [< inline >] sock_sendmsg_nosec net/socket.c:621 >>> >> [<ffffffff86a6ea9f>] sock_sendmsg+0xcf/0x110 net/socket.c:631 >>> >> [<ffffffff86a6ee0b>] sock_write_iter+0x32b/0x620 net/socket.c:829 >>> >> [<ffffffff81a6f153>] do_iter_readv_writev+0x363/0x670 >>> >> fs/read_write.c:695 >>> >> [<ffffffff81a71ba1>] do_readv_writev+0x431/0x9b0 fs/read_write.c:872 >>> >> [<ffffffff81a726dc>] vfs_writev+0x8c/0xc0 fs/read_write.c:911 >>> >> [<ffffffff81a72825>] do_writev+0x115/0x2d0 fs/read_write.c:944 >>> >> [< inline >] SYSC_writev fs/read_write.c:1017 >>> >> [<ffffffff81a75fdc>] SyS_writev+0x2c/0x40 fs/read_write.c:1014 >>> >> [<ffffffff8814cf85>] 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 [<ffffffff86be3295>] eth_header+0x75/0x260 net/ethernet/eth.c:88 >>> >> RSP <ffff880034d0eb68> >>> >> 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.
Eric, Is it enough to debug? Or maybe Andrey can trace some values for you.
