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Message-ID: <20251106175926.686885-1-kuniyu@google.com>
Date: Thu, 6 Nov 2025 17:59:17 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: syzbot+cif2d6d318f7e85f0b@...kaller.appspotmail.com
Cc: davem@...emloft.net, edumazet@...gle.com, hoang.h.le@...tech.com.au,
horms@...nel.org, jmaloy@...hat.com, kuba@...nel.org, kuni1840@...il.com,
kuniyu@...gle.com, netdev@...r.kernel.org, pabeni@...hat.com,
syzbot@...ts.linux.dev, syzbot@...kaller.appspotmail.com,
syzkaller-bugs@...glegroups.com, tipc-discussion@...ts.sourceforge.net
Subject: [syzbot ci] Re: tipc: Fix use-after-free in tipc_mon_reinit_self().
From: syzbot ci <syzbot+cif2d6d318f7e85f0b@...kaller.appspotmail.com>
Date: Thu, 06 Nov 2025 01:38:49 -0800
> syzbot ci has tested the following series
>
> [v1] tipc: Fix use-after-free in tipc_mon_reinit_self().
> https://lore.kernel.org/all/20251106053309.401275-1-kuniyu@google.com
> * [PATCH v1 net] tipc: Fix use-after-free in tipc_mon_reinit_self().
>
> and found the following issue:
> possible deadlock in tipc_mon_reinit_self
>
> Full report is available here:
> https://ci.syzbot.org/series/bfabf013-65e3-4ca9-8f54-0c7eef8be01a
>
> ***
>
> possible deadlock in tipc_mon_reinit_self
>
> tree: net
> URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
> base: 3d18a84eddde169d6dbf3c72cc5358b988c347d0
> arch: amd64
> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> config: https://ci.syzbot.org/builds/b2774856-e331-420e-a340-5107ec4b06f9/config
> C repro: https://ci.syzbot.org/findings/1f0a4298-b797-4217-8d6d-15f98c0ffd38/c_repro
> syz repro: https://ci.syzbot.org/findings/1f0a4298-b797-4217-8d6d-15f98c0ffd38/syz_repro
>
> tipc: Started in network mode
> tipc: Node identity 4, cluster identity 4711
> tipc: Node number set to 4
> ============================================
> WARNING: possible recursive locking detected
> syzkaller #0 Not tainted
> --------------------------------------------
> syz.0.17/5963 is trying to acquire lock:
> ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: tipc_mon_reinit_self+0x25/0x360 net/tipc/monitor.c:714
>
> but task is already holding lock:
> ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: __tipc_nl_compat_doit net/tipc/netlink_compat.c:358 [inline]
> ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: tipc_nl_compat_doit+0x1fd/0x5f0 net/tipc/netlink_compat.c:393
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(rtnl_mutex);
> lock(rtnl_mutex);
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 3 locks held by syz.0.17/5963:
> #0: ffffffff8f331050 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
> #1: ffffffff8f330e68 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline]
> #1: ffffffff8f330e68 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline]
> #1: ffffffff8f330e68 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10d/0x790 net/netlink/genetlink.c:1209
> #2: ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: __tipc_nl_compat_doit net/tipc/netlink_compat.c:358 [inline]
> #2: ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: tipc_nl_compat_doit+0x1fd/0x5f0 net/tipc/netlink_compat.c:393
>
> stack backtrace:
> CPU: 1 UID: 0 PID: 5963 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
> print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041
> check_deadlock kernel/locking/lockdep.c:3093 [inline]
> validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
> __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
> lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
> __mutex_lock_common kernel/locking/mutex.c:598 [inline]
> __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
> tipc_mon_reinit_self+0x25/0x360 net/tipc/monitor.c:714
> tipc_net_finalize+0x115/0x190 net/tipc/net.c:140
> tipc_net_init+0x104/0x190 net/tipc/net.c:122
> __tipc_nl_net_set+0x3b9/0x5a0 net/tipc/net.c:263
I missed another path calling tipc_net_finalize under RTNL.
I'll change v2 this way.
---8<---
diff --git a/net/tipc/monitor.c b/net/tipc/monitor.c
index 46c8814c3ee6..be1e51efc445 100644
--- a/net/tipc/monitor.c
+++ b/net/tipc/monitor.c
@@ -706,12 +706,13 @@ void tipc_mon_delete(struct net *net, int bearer_id)
kfree(mon);
}
-void tipc_mon_reinit_self(struct net *net)
+void tipc_mon_reinit_self(struct net *net, bool rtnl_held)
{
struct tipc_monitor *mon;
int bearer_id;
- rtnl_lock();
+ if (!rtnl_held)
+ rtnl_lock();
for (bearer_id = 0; bearer_id < MAX_BEARERS; bearer_id++) {
mon = tipc_monitor(net, bearer_id);
@@ -723,7 +724,8 @@ void tipc_mon_reinit_self(struct net *net)
write_unlock_bh(&mon->lock);
}
- rtnl_unlock();
+ if (!rtnl_held)
+ rtnl_unlock();
}
int tipc_nl_monitor_set_threshold(struct net *net, u32 cluster_size)
diff --git a/net/tipc/net.c b/net/tipc/net.c
index 0e95572e56b4..56527f6f548c 100644
--- a/net/tipc/net.c
+++ b/net/tipc/net.c
@@ -119,11 +119,11 @@ int tipc_net_init(struct net *net, u8 *node_id, u32 addr)
if (node_id)
tipc_set_node_id(net, node_id);
if (addr)
- tipc_net_finalize(net, addr);
+ tipc_net_finalize(net, addr, true);
return 0;
}
-static void tipc_net_finalize(struct net *net, u32 addr)
+static void tipc_net_finalize(struct net *net, u32 addr, bool rtnl_held)
{
struct tipc_net *tn = tipc_net(net);
struct tipc_socket_addr sk = {0, addr};
@@ -137,7 +137,7 @@ static void tipc_net_finalize(struct net *net, u32 addr)
tipc_set_node_addr(net, addr);
tipc_named_reinit(net);
tipc_sk_reinit(net);
- tipc_mon_reinit_self(net);
+ tipc_mon_reinit_self(net, rtnl_held);
tipc_nametbl_publish(net, &ua, &sk, addr);
}
@@ -145,7 +145,7 @@ void tipc_net_finalize_work(struct work_struct *work)
{
struct tipc_net *tn = container_of(work, struct tipc_net, work);
- tipc_net_finalize(tipc_link_net(tn->bcl), tn->trial_addr);
+ tipc_net_finalize(tipc_link_net(tn->bcl), tn->trial_addr, false);
}
void tipc_net_stop(struct net *net)
---8<---
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