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Message-ID: <20241126142031.11397-1-kuniyu@amazon.com>
Date: Tue, 26 Nov 2024 23:20:31 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <ebiederm@...ssion.com>, <jmaloy@...hat.com>,
<kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
<netdev@...r.kernel.org>, <pabeni@...hat.com>, <syzkaller@...glegroups.com>,
<tipc-discussion@...ts.sourceforge.net>, <ying.xue@...driver.com>,
<erik.hugne@...csson.com>
Subject: Re: [PATCH v1 net] tipc: Fix use-after-free of kernel socket in cleanup_bearer().
From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 26 Nov 2024 11:53:07 +0100
> On Tue, Nov 26, 2024 at 7:14 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > 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@...000009b3d1faf 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@...glegroups.com>
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.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(+)
> >
> > diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
> > index 439f75539977..10986b283ac8 100644
> > --- a/net/tipc/udp_media.c
> > +++ b/net/tipc/udp_media.c
> > @@ -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;
>
> I think 'kernel sockets' were not refcounted to allow the netns to be removed.
>
> Otherwise, what would tipc_bearer_stop() be needed ?
Interestingly, the delayed cleanup exists since the udp media support
was added in d0f91938bede2, and it's 2 months earlier than 26abe14379f8
that drops netns refcnt for kernel sockets.
So I thought the udp bearer did not assume bearer_disable() was called
from the __net_exit path, it could be simply wrong though.
At least, the __net_exit path works for other media types.
@Erik Hugne, do you remember any context above ?
>
> tipc_exit_net(struct net *net) // can only be called when all refcnt
> have been released
> -> tipc_net_stop()
> -> tipc_bearer_stop()
> -> bearer_disable()
> -> tipc_udp_disable()
> -> INIT_WORK(&ub->work, cleanup_bearer); schedule_work(&ub->work);
>
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