Subject: general protection fault in khugepaged

From: syzbot <[email-masked]>
Date: Wed, 08 Jul 2020 23:43:19 -0700

Hello,

syzbot found the following crash on:

HEAD commit:    e44f65fd xen-netfront: remove redundant assignment to vari..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15de54a7100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=829871134ca5e230
dashboard link: https://syzkaller.appspot.com/bug?extid=ed318e8b790ca72c5ad0
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=113406a7100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=175597d3100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 PID: 1155 Comm: khugepaged Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:anon_vma_lock_write include/linux/rmap.h:120 [inline]
RIP: 0010:collapse_huge_page mm/khugepaged.c:1110 [inline]
RIP: 0010:khugepaged_scan_pmd mm/khugepaged.c:1349 [inline]
RIP: 0010:khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline]
RIP: 0010:khugepaged_do_scan mm/khugepaged.c:2193 [inline]
RIP: 0010:khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238
Code: 01 00 00 48 8d bb 88 00 00 00 48 89 f8 48 c1 e8 03 42 80 3c 30 00 0f 85 fa 0f 00 00 48 8b 9b 88 00 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 d4 0f 00 00 48 8b 3b 48 83 c7 08 e8 9f ff 30
RSP: 0018:ffffc90004be7c80 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81a72d8b
RDX: ffff8880a69d8100 RSI: ffffffff81b7606b RDI: ffff88809f0577c0
RBP: 0000000000000000 R08: 0000000000000000 R09: ffff8881ff213a7f
R10: 0000000000000080 R11: 0000000000000000 R12: ffffffff8aae6110
R13: ffffc90004be7de0 R14: dffffc0000000000 R15: 0000000020000000
FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000001fe0cf000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
Modules linked in:
---[ end trace f1f03dbd2ea0777e ]---
RIP: 0010:anon_vma_lock_write include/linux/rmap.h:120 [inline]
RIP: 0010:collapse_huge_page mm/khugepaged.c:1110 [inline]
RIP: 0010:khugepaged_scan_pmd mm/khugepaged.c:1349 [inline]
RIP: 0010:khugepaged_scan_mm_slot mm/khugepaged.c:2110 [inline]
RIP: 0010:khugepaged_do_scan mm/khugepaged.c:2193 [inline]
RIP: 0010:khugepaged+0x3bba/0x5a10 mm/khugepaged.c:2238
Code: 01 00 00 48 8d bb 88 00 00 00 48 89 f8 48 c1 e8 03 42 80 3c 30 00 0f 85 fa 0f 00 00 48 8b 9b 88 00 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 d4 0f 00 00 48 8b 3b 48 83 c7 08 e8 9f ff 30
RSP: 0018:ffffc90004be7c80 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81a72d8b
RDX: ffff8880a69d8100 RSI: ffffffff81b7606b RDI: ffff88809f0577c0
RBP: 0000000000000000 R08: 0000000000000000 R09: ffff8881ff213a7f
R10: 0000000000000080 R11: 0000000000000000 R12: ffffffff8aae6110
R13: ffffc90004be7de0 R14: dffffc0000000000 R15: 0000000020000000
FS:  0000000000000000(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004c00c8 CR3: 00000001f7ac5000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

---
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