🟡 tipc: fix NULL pointer dereference in tipc_mon_reinit_self() (Linux Linux)

Description

In the Linux kernel, the following vulnerability has been resolved: tipc: fix NULL pointer dereference in tipc_mon_reinit_self() syzbot reported: tipc: Node number set to 1055423674 Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 3 UID: 0 PID: 6017 Comm: kworker/3:5 Not tainted 6.15.0-rc1-syzkaller-00246-g900241a5cc15 #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: events tipc_net_finalize_work RIP: 0010:tipc_mon_reinit_self+0x11c/0x210 net/tipc/monitor.c:719 ... RSP: 0018:ffffc9000356fb68 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000003ee87cba RDX: 0000000000000000 RSI: ffffffff8dbc56a7 RDI: ffff88804c2cc010 RBP: dffffc0000000000 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000007 R13: fffffbfff2111097 R14: ffff88804ead8000 R15: ffff88804ead9010 FS: 0000000000000000(0000) GS:ffff888097ab9000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000f720eb00 CR3: 000000000e182000 CR4: 0000000000352ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> tipc_net_finalize+0x10b/0x180 net/tipc/net.c:140 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400 kthread+0x3c2/0x780 kernel/kthread.c:464 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> ... RIP: 0010:tipc_mon_reinit_self+0x11c/0x210 net/tipc/monitor.c:719 ... RSP: 0018:ffffc9000356fb68 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000003ee87cba RDX: 0000000000000000 RSI: ffffffff8dbc56a7 RDI: ffff88804c2cc010 RBP: dffffc0000000000 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000007 R13: fffffbfff2111097 R14: ffff88804ead8000 R15: ffff88804ead9010 FS: 0000000000000000(0000) GS:ffff888097ab9000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000f720eb00 CR3: 000000000e182000 CR4: 0000000000352ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 There is a racing condition between workqueue created when enabling bearer and another thread created when disabling bearer right after that as follow: enabling_bearer | disabling_bearer --------------- | ---------------- tipc_disc_timeout() | { | bearer_disable() ... | { schedule_work(&tn->work); | tipc_mon_delete() ... | { } | ... | write_lock_bh(&mon->lock); | mon->self = NULL; | write_unlock_bh(&mon->lock); | ... | } tipc_net_finalize_work() | } { | ... | tipc_net_finalize() | { | ... | tipc_mon_reinit_self() | { | ... | write_lock_bh(&mon->lock); | mon->self->addr = tipc_own_addr(net); | write_unlock_bh(&mon->lock); | ... ---truncated---