BUG: kernel NULL pointer dereference, address: 000000000000009c #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 10cab3067 P4D 10cab3067 PUD 107c62067 PMD 0 Oops: 0000 [#1] PREEMPT SMP CPU: 0 PID: 8426 Comm: syz-fuzzer Not tainted 5.9.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:kcsan_setup_watchpoint+0x215/0x4d0 kernel/kcsan/core.c:479 Code: 9d 4c 89 74 24 50 eb 05 ff 74 24 50 9d 48 83 c4 60 5b 41 5c 41 5d 41 5e 41 5f 5d c3 0f b7 08 89 ca c1 ea 08 31 db 31 f6 eb 26 <8b> 08 89 ca c1 ea 08 89 ce c1 ee 10 eb 18 48 8b 08 48 89 ca 48 c1 RSP: 0018:ffffc90000003de0 EFLAGS: 00010046 RAX: 000000000000009c RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000003 R08: 00000000aaaaaaab R09: 000800000000009c R10: 0000000000000246 R11: ffff888102431000 R12: 0000000000000004 R13: 0000000000000000 R14: ffffe8ffffc043c0 R15: 0000000000000001 FS: 0000000001a76550(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000000009c CR3: 000000010b206000 CR4: 00000000001526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: afs_unuse_cell+0x24/0x2b0 fs/afs/cell.c:592 afs_cell_destroy+0xa1/0x210 fs/afs/cell.c:500 rcu_do_batch kernel/rcu/tree.c:2476 [inline] rcu_core+0x6bb/0xbc0 kernel/rcu/tree.c:2711 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2724 __do_softirq+0x12c/0x2b1 kernel/softirq.c:298 asm_call_irq_on_stack+0xf/0x20 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline] run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline] do_softirq_own_stack+0x32/0x40 arch/x86/kernel/irq_64.c:77 do_softirq kernel/softirq.c:343 [inline] __local_bh_enable_ip+0xba/0xd0 kernel/softirq.c:195 local_bh_enable+0x1b/0x20 include/linux/bottom_half.h:32 rcu_read_unlock_bh include/linux/rcupdate.h:730 [inline] ip_finish_output2+0xb10/0xba0 net/ipv4/ip_output.c:231 __ip_finish_output+0x3d8/0x430 net/ipv4/ip_output.c:308 ip_finish_output+0x39/0x160 net/ipv4/ip_output.c:318 NF_HOOK_COND include/linux/netfilter.h:290 [inline] ip_output+0xf6/0x1a0 net/ipv4/ip_output.c:432 dst_output include/net/dst.h:443 [inline] ip_local_out net/ipv4/ip_output.c:126 [inline] __ip_queue_xmit+0x9ca/0x9f0 net/ipv4/ip_output.c:532 ip_queue_xmit+0x34/0x40 net/ipv4/ip_output.c:546 __tcp_transmit_skb+0x1250/0x1860 net/ipv4/tcp_output.c:1404 tcp_transmit_skb net/ipv4/tcp_output.c:1422 [inline] tcp_write_xmit+0x10bd/0x3c60 net/ipv4/tcp_output.c:2684 __tcp_push_pending_frames+0x68/0x1c0 net/ipv4/tcp_output.c:2862 tcp_push+0x2cd/0x2e0 net/ipv4/tcp.c:735 tcp_sendmsg_locked+0x1c2d/0x2130 net/ipv4/tcp.c:1412 tcp_sendmsg+0x2c/0x40 net/ipv4/tcp.c:1442 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:817 sock_sendmsg_nosec net/socket.c:651 [inline] sock_sendmsg net/socket.c:671 [inline] sock_write_iter+0x1a4/0x200 net/socket.c:998 call_write_iter include/linux/fs.h:1887 [inline] new_sync_write fs/read_write.c:518 [inline] vfs_write+0x617/0x690 fs/read_write.c:605 ksys_write+0xce/0x180 fs/read_write.c:658 __do_sys_write fs/read_write.c:670 [inline] __se_sys_write fs/read_write.c:667 [inline] __x64_sys_write+0x3e/0x50 fs/read_write.c:667 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x4b3cdb Code: ff e9 69 ff ff ff cc cc cc cc cc cc cc cc cc e8 bb a1 f8 ff 48 8b 7c 24 10 48 8b 74 24 18 48 8b 54 24 20 48 8b 44 24 08 0f 05 <48> 3d 01 f0 ff ff 76 20 48 c7 44 24 28 ff ff ff ff 48 c7 44 24 30 RSP: 002b:000000c000a8f690 EFLAGS: 00000206 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 000000c00002e800 RCX: 00000000004b3cdb RDX: 00000000000000f0 RSI: 000000c00000a200 RDI: 0000000000000006 RBP: 000000c000a8f6e0 R08: 000000c00000a201 R09: 00000000000000f0 R10: 000000c000114900 R11: 0000000000000206 R12: 000000000000011e R13: 000000c000210000 R14: 000000000000007f R15: ffffffffffff0644 Modules linked in: CR2: 000000000000009c ---[ end trace ee2e05c140b2bf5a ]--- RIP: 0010:kcsan_setup_watchpoint+0x215/0x4d0 kernel/kcsan/core.c:479 Code: 9d 4c 89 74 24 50 eb 05 ff 74 24 50 9d 48 83 c4 60 5b 41 5c 41 5d 41 5e 41 5f 5d c3 0f b7 08 89 ca c1 ea 08 31 db 31 f6 eb 26 <8b> 08 89 ca c1 ea 08 89 ce c1 ee 10 eb 18 48 8b 08 48 89 ca 48 c1 RSP: 0018:ffffc90000003de0 EFLAGS: 00010046 RAX: 000000000000009c RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000003 R08: 00000000aaaaaaab R09: 000800000000009c R10: 0000000000000246 R11: ffff888102431000 R12: 0000000000000004 R13: 0000000000000000 R14: ffffe8ffffc043c0 R15: 0000000000000001 FS: 0000000001a76550(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000000009c CR3: 000000010b206000 CR4: 00000000001526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400