@@ -673,6 +673,7 @@ static int tipc_udp_enable(struct net *net, struct tipc_bearer *b,
struct nlattr *opts[TIPC_NLA_UDP_MAX + 1];
u8 node_id[NODE_ID_LEN] = {0,};
struct net_device *dev;
+ struct sock *sk;
int rmcast = 0;
ub = kzalloc(sizeof(*ub), GFP_ATOMIC);
@@ -792,6 +793,12 @@ static int tipc_udp_enable(struct net *net, struct tipc_bearer *b,
if (err)
goto free;
+ sk = ub->ubsock->sk;
+ __netns_tracker_free(net, &sk->ns_tracker, false);
+ sk->sk_net_refcnt = 1;
+ get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
+ sock_inuse_add(net, 1);
+
return 0;
free:
syzkaller reported a use-after-free of kernel UDP socket in cleanup_bearer() without repro. [0][1] When bearer_disable() calls tipc_udp_disable(), cleanup of the kernel UDP socket is deferred by work calling cleanup_bearer(). Since the cited commit, however, the socket's netns might not be alive when the work is executed, resulting in use-after-free. Let's hold netns for the kernel UDP socket when created. Note that we can't call get_net() before scheduling the work and call put_net() in cleanup_bearer() because bearer_disable() could be called from pernet_operations.exit(): tipc_exit_net `- tipc_net_stop `- tipc_bearer_stop `- bearer_disable [0]: ref_tracker: net notrefcnt@000000009b3d1faf has 1/1 users at sk_alloc+0x438/0x608 inet_create+0x4c8/0xcb0 __sock_create+0x350/0x6b8 sock_create_kern+0x58/0x78 udp_sock_create4+0x68/0x398 udp_sock_create+0x88/0xc8 tipc_udp_enable+0x5e8/0x848 __tipc_nl_bearer_enable+0x84c/0xed8 tipc_nl_bearer_enable+0x38/0x60 genl_family_rcv_msg_doit+0x170/0x248 genl_rcv_msg+0x400/0x5b0 netlink_rcv_skb+0x1dc/0x398 genl_rcv+0x44/0x68 netlink_unicast+0x678/0x8b0 netlink_sendmsg+0x5e4/0x898 ____sys_sendmsg+0x500/0x830 [1]: BUG: KMSAN: use-after-free in udp_hashslot include/net/udp.h:85 [inline] BUG: KMSAN: use-after-free in udp_lib_unhash+0x3b8/0x930 net/ipv4/udp.c:1979 udp_hashslot include/net/udp.h:85 [inline] udp_lib_unhash+0x3b8/0x930 net/ipv4/udp.c:1979 sk_common_release+0xaf/0x3f0 net/core/sock.c:3820 inet_release+0x1e0/0x260 net/ipv4/af_inet.c:437 inet6_release+0x6f/0xd0 net/ipv6/af_inet6.c:489 __sock_release net/socket.c:658 [inline] sock_release+0xa0/0x210 net/socket.c:686 cleanup_bearer+0x42d/0x4c0 net/tipc/udp_media.c:819 process_one_work kernel/workqueue.c:3229 [inline] process_scheduled_works+0xcaf/0x1c90 kernel/workqueue.c:3310 worker_thread+0xf6c/0x1510 kernel/workqueue.c:3391 kthread+0x531/0x6b0 kernel/kthread.c:389 ret_from_fork+0x60/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244 Uninit was created at: slab_free_hook mm/slub.c:2269 [inline] slab_free mm/slub.c:4580 [inline] kmem_cache_free+0x207/0xc40 mm/slub.c:4682 net_free net/core/net_namespace.c:454 [inline] cleanup_net+0x16f2/0x19d0 net/core/net_namespace.c:647 process_one_work kernel/workqueue.c:3229 [inline] process_scheduled_works+0xcaf/0x1c90 kernel/workqueue.c:3310 worker_thread+0xf6c/0x1510 kernel/workqueue.c:3391 kthread+0x531/0x6b0 kernel/kthread.c:389 ret_from_fork+0x60/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:244 CPU: 0 UID: 0 PID: 54 Comm: kworker/0:2 Not tainted 6.12.0-rc1-00131-gf66ebf37d69c #7 91723d6f74857f70725e1583cba3cf4adc716cfa Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 Workqueue: events cleanup_bearer Fixes: 26abe14379f8 ("net: Modify sk_alloc to not reference count the netns of kernel sockets.") Reported-by: syzkaller <syzkaller@googlegroups.com> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> --- I'll remove this ugly hack by clearner API in the next cycle. see: https://lore.kernel.org/netdev/20241112001308.58355-1-kuniyu@amazon.com/ --- net/tipc/udp_media.c | 7 +++++++ 1 file changed, 7 insertions(+)