Re: BUG: unable to handle kernel NULL pointer dereference in xsk_poll

[Magnus Karlsson]

On Mon, Sep 30, 2019 at 9:17 AM syzbot
<syzbot+a5765ed8cdb1cca4d249@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:

Thank you Mr Syzcaller. I am on it.

/Magnus

> HEAD commit:    a3c0e7b1 Merge tag 'libnvdimm-fixes-5.4-rc1' of git://git...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14f05435600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6ffbfa7e4a36190f
> dashboard link: https://syzkaller.appspot.com/bug?extid=a5765ed8cdb1cca4d249
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1096d835600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=129f15f3600000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+a5765ed8cdb1cca4d249@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
> 8021q: adding VLAN 0 to HW filter on device batadv0
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> #PF: supervisor instruction fetch in kernel mode
> #PF: error_code(0x0010) - not-present page
> PGD 99226067 P4D 99226067 PUD 8fa47067 PMD 0
> Oops: 0010 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 8719 Comm: syz-executor502 Not tainted 5.3.0+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:0x0
> Code: Bad RIP value.
> RSP: 0018:ffff88809dd4f848 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff88808c06d740 RCX: 1ffff1101180db7c
> RDX: 0000000000000002 RSI: 0000000000000000 RDI: ffff88809a190b00
> RBP: ffff88809dd4f880 R08: ffff8880921924c0 R09: ffffed101180db31
> R10: ffffed101180db30 R11: ffff88808c06d987 R12: 0000000000000002
> R13: 0000000000000304 R14: ffff88809a190b00 R15: 0000000000000000
> FS:  0000000001b27880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffffffffd6 CR3: 00000000a307a000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   xsk_poll+0x1e7/0x5a0 net/xdp/xsk.c:430
>   sock_poll+0x15e/0x480 net/socket.c:1256
>   vfs_poll include/linux/poll.h:90 [inline]
>   do_pollfd fs/select.c:859 [inline]
>   do_poll fs/select.c:907 [inline]
>   do_sys_poll+0x63c/0xdd0 fs/select.c:1001
>   __do_sys_ppoll fs/select.c:1101 [inline]
>   __se_sys_ppoll fs/select.c:1081 [inline]
>   __x64_sys_ppoll+0x259/0x310 fs/select.c:1081
>   do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x441bd9
> Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> ff 0f 83 7b 10 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffd48824e98 EFLAGS: 00000246 ORIG_RAX: 000000000000010f
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000441bd9
> RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000020000040
> RBP: 00007ffd48824eb0 R08: 0000000000000000 R09: 0000000001bbbbbb
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000403170 R14: 0000000000000000 R15: 0000000000000000
> Modules linked in:
> CR2: 0000000000000000
> ---[ end trace e262cafe88422aec ]---
> RIP: 0010:0x0
> Code: Bad RIP value.
> RSP: 0018:ffff88809dd4f848 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff88808c06d740 RCX: 1ffff1101180db7c
> RDX: 0000000000000002 RSI: 0000000000000000 RDI: ffff88809a190b00
> RBP: ffff88809dd4f880 R08: ffff8880921924c0 R09: ffffed101180db31
> R10: ffffed101180db30 R11: ffff88808c06d987 R12: 0000000000000002
> R13: 0000000000000304 R14: ffff88809a190b00 R15: 0000000000000000
> FS:  0000000001b27880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffffffffd6 CR3: 00000000a307a000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
> ---
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