BUG: unable to handle kernel NULL pointer dereference in qlist_free_all (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    34d4ddd3 Merge tag 'linux-kselftest-5.9-rc5' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=147c760d900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a9075b36a6ae26c9
dashboard link: https://syzkaller.appspot.com/bug?extid=4bba137eaf7cc94b57ca
compiler:       gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4bba137eaf7cc94b57ca at syzkaller.appspotmail.com

BUG: kernel NULL pointer dereference, address: 0000000000000080
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 4bbac067 P4D 4bbac067 PUD 9468a067 PMD 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 3936 Comm: syz-executor.0 Not tainted 5.9.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:qlink_to_object mm/kasan/quarantine.c:137 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:142 [inline]
RIP: 0010:qlist_free_all+0x36/0x170 mm/kasan/quarantine.c:168
Code: 53 48 83 ec 10 48 8b 37 48 85 f6 0f 84 36 01 00 00 49 bf 00 00 00 00 00 fc ff df 48 85 ed 49 89 fd 48 89 ef 0f 84 97 00 00 00 <48> 63 87 80 00 00 00 4c 8b 26 48 29 c6 48 83 3d 75 e5 01 08 00 0f
RSP: 0018:ffffc90004dd7a10 EFLAGS: 00010246
RAX: ffffea0000000000 RBX: 0000000000000282 RCX: ffffea0000000007
RDX: 0000000000000000 RSI: ffff888000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffffff8c5f5a77
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888000000000
R13: ffffc90004dd7a58 R14: 0000000000000200 R15: dffffc0000000000
FS:  0000000003563940(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 000000003d19c000 CR4: 00000000001526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 quarantine_reduce+0x17e/0x200 mm/kasan/quarantine.c:261
 __kasan_kmalloc.constprop.0+0x9e/0xd0 mm/kasan/common.c:442
 slab_post_alloc_hook mm/slab.h:518 [inline]
 slab_alloc mm/slab.c:3312 [inline]
 __do_kmalloc mm/slab.c:3653 [inline]
 __kmalloc+0x178/0x310 mm/slab.c:3664
 kmalloc include/linux/slab.h:559 [inline]
 kzalloc include/linux/slab.h:666 [inline]
 tomoyo_encode2.part.0+0xe9/0x3a0 security/tomoyo/realpath.c:45
 tomoyo_encode2 security/tomoyo/realpath.c:31 [inline]
 tomoyo_encode+0x28/0x50 security/tomoyo/realpath.c:80
 tomoyo_path_perm+0x35f/0x3f0 security/tomoyo/file.c:831
 tomoyo_path_symlink+0x94/0xe0 security/tomoyo/tomoyo.c:200
 security_path_symlink+0xdf/0x150 security/security.c:1109
 do_symlinkat+0x123/0x2c0 fs/namei.c:3984
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d2e7
Code: 0f 1f 00 b8 5c 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 1d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 58 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 fd b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:000000000169fda8 EFLAGS: 00000202 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000045d2e7
RDX: 000000000169fe43 RSI: 00000000004c30cd RDI: 000000000169fe30
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000013
R10: 0000000000000075 R11: 0000000000000202 R12: 0000000000000000
R13: 000000000169fde0 R14: 0000000000000000 R15: 000000000169fdf0
Modules linked in:
CR2: 0000000000000080
---[ end trace 9fd83eee6918f461 ]---
RIP: 0010:qlink_to_object mm/kasan/quarantine.c:137 [inline]
RIP: 0010:qlink_free mm/kasan/quarantine.c:142 [inline]
RIP: 0010:qlist_free_all+0x36/0x170 mm/kasan/quarantine.c:168
Code: 53 48 83 ec 10 48 8b 37 48 85 f6 0f 84 36 01 00 00 49 bf 00 00 00 00 00 fc ff df 48 85 ed 49 89 fd 48 89 ef 0f 84 97 00 00 00 <48> 63 87 80 00 00 00 4c 8b 26 48 29 c6 48 83 3d 75 e5 01 08 00 0f
RSP: 0018:ffffc90004dd7a10 EFLAGS: 00010246
RAX: ffffea0000000000 RBX: 0000000000000282 RCX: ffffea0000000007
RDX: 0000000000000000 RSI: ffff888000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffffff8c5f5a77
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888000000000
R13: ffffc90004dd7a58 R14: 0000000000000200 R15: dffffc0000000000
FS:  0000000003563940(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000749198 CR3: 000000003d19c000 CR4: 00000000001526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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