netdev - [PATCH v1 net] tipc: Fix use-after-free in tipc_conn

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Message-ID: <20250702014350.692213-1-kuniyu@google.com>
Date: Wed,  2 Jul 2025 01:43:40 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Jon Maloy <jmaloy@...hat.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Ying Xue <ying.xue@...driver.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	tipc-discussion@...ts.sourceforge.net, 
	syzbot+d333febcf8f4bc5f6110@...kaller.appspotmail.com
Subject: [PATCH v1 net] tipc: Fix use-after-free in tipc_conn_close().

syzbot reported a null-ptr-deref in tipc_conn_close() during netns
dismantle. [0]

tipc_topsrv_stop() iterates tipc_net(net)->topsrv->conn_idr and calls
tipc_conn_close() for each tipc_conn.

The problem is that tipc_conn_close() is called after releasing the
IDR lock.

At the same time, there might be tipc_conn_recv_work() running and it
could call tipc_conn_close() for the same tipc_conn and release its
last ->kref.

Once we release the IDR lock in tipc_topsrv_stop(), there is no
guarantee that the tipc_conn is alive.

Let's hold the ref before releasing the lock and put the ref after
tipc_conn_close() in tipc_topsrv_stop().

[0]:
BUG: KASAN: use-after-free in tipc_conn_close+0x122/0x140 net/tipc/topsrv.c:165
Read of size 8 at addr ffff888099305a08 by task kworker/u4:3/435

CPU: 0 PID: 435 Comm: kworker/u4:3 Not tainted 4.19.204-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
 print_address_description.cold+0x54/0x219 mm/kasan/report.c:256
 kasan_report_error.cold+0x8a/0x1b9 mm/kasan/report.c:354
 kasan_report mm/kasan/report.c:412 [inline]
 __asan_report_load8_noabort+0x88/0x90 mm/kasan/report.c:433
 tipc_conn_close+0x122/0x140 net/tipc/topsrv.c:165
 tipc_topsrv_stop net/tipc/topsrv.c:701 [inline]
 tipc_topsrv_exit_net+0x27b/0x5c0 net/tipc/topsrv.c:722
 ops_exit_list+0xa5/0x150 net/core/net_namespace.c:153
 cleanup_net+0x3b4/0x8b0 net/core/net_namespace.c:553
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
 kthread+0x33f/0x460 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 23:
 kmem_cache_alloc_trace+0x12f/0x380 mm/slab.c:3625
 kmalloc include/linux/slab.h:515 [inline]
 kzalloc include/linux/slab.h:709 [inline]
 tipc_conn_alloc+0x43/0x4f0 net/tipc/topsrv.c:192
 tipc_topsrv_accept+0x1b5/0x280 net/tipc/topsrv.c:470
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
 kthread+0x33f/0x460 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Freed by task 23:
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xcc/0x210 mm/slab.c:3822
 tipc_conn_kref_release net/tipc/topsrv.c:150 [inline]
 kref_put include/linux/kref.h:70 [inline]
 conn_put+0x2cd/0x3a0 net/tipc/topsrv.c:155
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
 kthread+0x33f/0x460 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

The buggy address belongs to the object at ffff888099305a00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
 512-byte region [ffff888099305a00, ffff888099305c00)
The buggy address belongs to the page:
page:ffffea000264c140 count:1 mapcount:0 mapping:ffff88813bff0940 index:0x0
flags: 0xfff00000000100(slab)
raw: 00fff00000000100 ffffea00028b6b88 ffffea0002cd2b08 ffff88813bff0940
raw: 0000000000000000 ffff888099305000 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888099305900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888099305980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888099305a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff888099305a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888099305b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Fixes: c5fa7b3cf3cb ("tipc: introduce new TIPC server infrastructure")
Reported-by: syzbot+d333febcf8f4bc5f6110@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=27169a847a70550d17be
Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
 net/tipc/topsrv.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/tipc/topsrv.c b/net/tipc/topsrv.c
index 8ee0c07d00e9..ffe577bf6b51 100644
--- a/net/tipc/topsrv.c
+++ b/net/tipc/topsrv.c
@@ -704,8 +704,10 @@ static void tipc_topsrv_stop(struct net *net)
 	for (id = 0; srv->idr_in_use; id++) {
 		con = idr_find(&srv->conn_idr, id);
 		if (con) {
+			conn_get(con);
 			spin_unlock_bh(&srv->idr_lock);
 			tipc_conn_close(con);
+			conn_put(con);
 			spin_lock_bh(&srv->idr_lock);
 		}
 	}
-- 
2.50.0.727.gbf7dc18ff4-goog