netdev - Re: [PATCH v1 net] tipc: Fix use-after-free of kernel socket in cleanup

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Message-ID: <CANn89iLXk2BRLWuyvEsxOVqRBo2qbuOydv33xfKAe54M9tKPUA@mail.gmail.com>
Date: Tue, 26 Nov 2024 11:53:07 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: Jon Maloy <jmaloy@...hat.com>, Ying Xue <ying.xue@...driver.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Eric W. Biederman" <ebiederm@...ssion.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	tipc-discussion@...ts.sourceforge.net, syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v1 net] tipc: Fix use-after-free of kernel socket in cleanup_bearer().

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 ?

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);