general protection fault in getname_kernel

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    c1d84a1b42ef Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10f3c6a1400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c0af03fe452b65fb
dashboard link: https://syzkaller.appspot.com/bug?extid=c54f8e94e6bba03b04e9
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10688159400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1162aa31400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c54f8e94e6bba03b04e9@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 5829 Comm: syz-executor215 Not tainted 4.19.0-rc6+ #271
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:strlen+0x1f/0xa0 lib/string.c:479
Code: ff ff ff 0f 1f 84 00 00 00 00 00 48 b8 00 00 00 00 00 fc ff df 55 48  
89 fa 48 89 e5 48 c1 ea 03 41 54 49 89 fc 53 48 83 ec 08 <0f> b6 04 02 48  
89 fa 83 e2 07 38 d0 7f 04 84 c0 75 4d 41 80 3c 24
RSP: 0018:ffff8801bc30f9b0 EFLAGS: 00010282
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffff8801bc74eec0
RDX: 0000000000000000 RSI: ffffffff81d2cccc RDI: 0000000000000000
RBP: ffff8801bc30f9c8 R08: ffff8801d7c24400 R09: ffffed003af0a800
R10: fffff94000ebc2a6 R11: ffffea00075e1537 R12: 0000000000000000
R13: 0000000000000000 R14: ffffffff89f3ee98 R15: 0000000000000000
FS:  0000000001f11880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 00000001d7cc6000 CR4: 00000000001406e0
Call Trace:
 strlen include/linux/string.h:267 [inline]
 getname_kernel+0x24/0x370 fs/namei.c:218
 kern_path+0x1e/0x40 fs/namei.c:2434
 gfs2_mount_meta+0x85/0x2a0 fs/gfs2/ops_fstype.c:1336
 mount_fs+0xae/0x31d fs/super.c:1261
 vfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
 vfs_kern_mount fs/namespace.c:951 [inline]
 do_new_mount fs/namespace.c:2457 [inline]
 do_mount+0x581/0x31f0 fs/namespace.c:2787
 ksys_mount+0x12d/0x140 fs/namespace.c:3003
 __do_sys_mount fs/namespace.c:3017 [inline]
 __se_sys_mount fs/namespace.c:3014 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3014
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440059
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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe32cedb58 EFLAGS: 00000217 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 0000000000440059
RDX: 0000000020000040 RSI: 0000000020000080 RDI: 0000000000000000
RBP: 00000000006ca018 R08: 00000000200000c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004018e0
R13: 0000000000401970 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace e8236b178a90d827 ]---
RIP: 0010:strlen+0x1f/0xa0 lib/string.c:479
Code: ff ff ff 0f 1f 84 00 00 00 00 00 48 b8 00 00 00 00 00 fc ff df 55 48  
89 fa 48 89 e5 48 c1 ea 03 41 54 49 89 fc 53 48 83 ec 08 <0f> b6 04 02 48  
89 fa 83 e2 07 38 d0 7f 04 84 c0 75 4d 41 80 3c 24
RSP: 0018:ffff8801bc30f9b0 EFLAGS: 00010282
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffff8801bc74eec0
RDX: 0000000000000000 RSI: ffffffff81d2cccc RDI: 0000000000000000
RBP: ffff8801bc30f9c8 R08: ffff8801d7c24400 R09: ffffed003af0a800
R10: fffff94000ebc2a6 R11: ffffea00075e1537 R12: 0000000000000000
R13: 0000000000000000 R14: ffffffff89f3ee98 R15: 0000000000000000
FS:  0000000001f11880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 00000001d7cc6000 CR4: 00000000001406e0


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