linux-kernel - Re: general protection fault in __handle_mm

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Date:   Mon, 8 Oct 2018 16:33:24 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     syzbot+1577fbe983d20fe2e88f@...kaller.appspotmail.com
Cc:     David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kirill.shutemov@...ux.intel.com, aneesh.kumar@...ux.ibm.com
Subject: Re: general protection fault in __handle_mm_fault

On Mon, Oct 8, 2018 at 12:10 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> On Fri, Oct 5, 2018 at 6:27 PM syzbot
> <syzbot+1577fbe983d20fe2e88f@...kaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    25bcda3e8b9f Add linux-next specific files for 20181004
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=130e3bf1400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=603d7f9140c3368a
> > dashboard link: https://syzkaller.appspot.com/bug?extid=1577fbe983d20fe2e88f
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=127e88d6400000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13cdb67e400000
>
> > RIP: 0010:copy_user_enhanced_fast_string+0xe/0x20
> > arch/x86/lib/copy_user_64.S:180
> > Code: 89 d1 c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 31 c0 0f 1f 00 c3 0f 1f
> > 80 00 00 00 00 0f 1f 00 83 fa 40 0f 82 70 ff ff ff 89 d1 <f3> a4 31 c0 0f
> > 1f 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 83
> > RSP: 0018:ffff8801bbe675b8 EFLAGS: 00010202
> > RAX: 0000000000000000 RBX: 0000000000007a50 RCX: 0000000000001b40
> > RDX: 0000000000007a50 RSI: 0000000020077000 RDI: ffff8801ce615f10
> > RBP: ffff8801bbe675f0 R08: ffffed0039cc2f4a R09: ffffed0039cc2f4a
> > R10: ffffed0039cc2f49 R11: ffff8801ce617a4f R12: 0000000020078b40
> > R13: 00000000200710f0 R14: ffff8801ce610000 R15: 00007ffffffff000
> >   _copy_from_iter_full+0x263/0xc20 lib/iov_iter.c:724
> >   copy_from_iter_full include/linux/uio.h:124 [inline]
> >   skb_do_copy_data_nocache include/net/sock.h:1951 [inline]
> >   skb_copy_to_page_nocache include/net/sock.h:1977 [inline]
> >   tcp_sendmsg_locked+0x159e/0x3f90 net/ipv4/tcp.c:1338
>
> This started on next-20181004. It still happens as of next-20181008.
>
> It does not trigger on next 20181003. It does not occur if
> CONFIG_DEBUG_KOBJECT is disabled.

Bisected to commit e4d0c281a4c9 ("mm/memory.c: recheck page table
entry with page table lock held").

Verified to not trigger on next-20181008 after reverting that commit.