netdev - Re: [PATCH v2 net] tipc: Fix use-after-free of kernel socket in cleanup

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Message-ID: <baca7f28-22c2-4d11-9894-ed97c8da7e23@stanley.mountain>
Date: Fri, 6 Dec 2024 14:00:32 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Kuniyuki Iwashima <kuniyu@...zon.com>, 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 v2 net] tipc: Fix use-after-free of kernel socket in
 cleanup_bearer().

On Wed, Dec 04, 2024 at 04:01:10PM +0100, Eric Dumazet wrote:
> On Wed, Nov 27, 2024 at 6:05 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > syzkaller reported a use-after-free of UDP kernel socket
> > in cleanup_bearer() without repro. [0][1]
> >
> > When bearer_disable() calls tipc_udp_disable(), cleanup
> > of the UDP kernel socket is deferred by work calling
> > cleanup_bearer().
> >
> > tipc_net_stop() waits for such works to finish by checking
> > tipc_net(net)->wq_count.  However, the work decrements the
> > count too early before releasing the kernel socket,
> > unblocking cleanup_net() and resulting in use-after-free.
> >
> > Let's move the decrement after releasing the socket in
> > cleanup_bearer().
> >
> > [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>
> > ---
> > v2:
> >   * Keep kernel socket with no net refcnt.
> >
> > v1: https://lore.kernel.org/netdev/20241126061446.64052-1-kuniyu@amazon.com/
> > ---
> >  net/tipc/udp_media.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
> > index 439f75539977..b7e25e7e9933 100644
> > --- a/net/tipc/udp_media.c
> > +++ b/net/tipc/udp_media.c
> > @@ -814,10 +814,10 @@ static void cleanup_bearer(struct work_struct *work)
> >                 kfree_rcu(rcast, rcu);
> >         }
> >
> > -       atomic_dec(&tipc_net(sock_net(ub->ubsock->sk))->wq_count);
> >         dst_cache_destroy(&ub->rcast.dst_cache);
> >         udp_tunnel_sock_release(ub->ubsock);
> >         synchronize_net();
> > +       atomic_dec(&tipc_net(sock_net(ub->ubsock->sk))->wq_count);
> 
> Note that ub->ubsock->sk is NULL at this point.
> 

Also udp_tunnel_sock_release() releases ub->ubsock so Smatch complains if
you have the cross function database.

regards,
dan carpenter