general protection fault in proc_kill_sb

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16e12212100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
dashboard link: https://syzkaller.appspot.com/bug?extid=4abac52934a48af5ff19
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4abac52934a48af5ff19@xxxxxxxxxxxxxxxxxxxxxxxxx

RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000000000000751 R14: 00000000004ca3ea R15: 00007f8970ff76d4
general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 6840 Comm: syz-executor.2 Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:proc_kill_sb+0x4d/0x110 fs/proc/root.c:267
Code: c1 ea 03 80 3c 02 00 0f 85 ad 00 00 00 49 8b ac 24 68 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7d 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 a1 00 00 00 4c 8b 6d 08 4d 85 ed 74 0d e8 cb 51
RSP: 0018:ffffc90007b67d48 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffc9000d6d1000
RDX: 0000000000000001 RSI: ffffffff81e37c9d RDI: 0000000000000008
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff8c347a2f R11: fffffbfff1868f45 R12: ffff888059e1a000
R13: 00000000fffffff4 R14: 0000000000000000 R15: ffff888059e1a068
FS:  00007f8970ff7700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000073c138 CR3: 00000000588dc000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 deactivate_locked_super+0x8c/0xf0 fs/super.c:335
 vfs_get_super+0x258/0x2d0 fs/super.c:1212
 vfs_get_tree+0x89/0x2f0 fs/super.c:1547
 do_new_mount fs/namespace.c:2874 [inline]
 do_mount+0x1306/0x1b40 fs/namespace.c:3199
 __do_sys_mount fs/namespace.c:3409 [inline]
 __se_sys_mount fs/namespace.c:3386 [inline]
 __x64_sys_mount+0x18f/0x230 fs/namespace.c:3386
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45ca69
Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8970ff6c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000004f62c0 RCX: 000000000045ca69
RDX: 00000000200000c0 RSI: 0000000020000200 RDI: 0000000020000340
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000000000000751 R14: 00000000004ca3ea R15: 00007f8970ff76d4
Modules linked in:
---[ end trace 7f26d357bd21d77e ]---
RIP: 0010:proc_kill_sb+0x4d/0x110 fs/proc/root.c:267
Code: c1 ea 03 80 3c 02 00 0f 85 ad 00 00 00 49 8b ac 24 68 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7d 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 a1 00 00 00 4c 8b 6d 08 4d 85 ed 74 0d e8 cb 51
RSP: 0018:ffffc90007b67d48 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffc9000d6d1000
RDX: 0000000000000001 RSI: ffffffff81e37c9d RDI: 0000000000000008
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff8c347a2f R11: fffffbfff1868f45 R12: ffff888059e1a000
R13: 00000000fffffff4 R14: 0000000000000000 R15: ffff888059e1a068
FS:  00007f8970ff7700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f19326ab000 CR3: 00000000588dc000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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