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Message-ID: <CANn89iJ-GfHU=sLWJiuqNcoH+AnBtj9dSxpXHjqbAS_VZ8fzAw@mail.gmail.com>
Date: Wed, 4 Dec 2024 16:01:10 +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 v2 net] tipc: Fix use-after-free of kernel socket in cleanup_bearer().
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.
I am testing the following fix, does it make sense to you ?
diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index b7e25e7e9933b69aa6a3364e3287c358b7ac9421..1d359de9dd6ad7ff60b6b93f620ff6783e385106
100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -807,6 +807,7 @@ static void cleanup_bearer(struct work_struct *work)
{
struct udp_bearer *ub = container_of(work, struct udp_bearer, work);
struct udp_replicast *rcast, *tmp;
+ struct tipc_net *tn;
list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {
dst_cache_destroy(&rcast->dst_cache);
@@ -814,10 +815,14 @@ static void cleanup_bearer(struct work_struct *work)
kfree_rcu(rcast, rcu);
}
+ tn = tipc_net(sock_net(ub->ubsock->sk));
+
dst_cache_destroy(&ub->rcast.dst_cache);
udp_tunnel_sock_release(ub->ubsock);
+
+ /* Note: we could use a call_rcu() to avoid another synchronize_net() */
synchronize_net();
- atomic_dec(&tipc_net(sock_net(ub->ubsock->sk))->wq_count);
+ atomic_dec(&tn->wq_count);
kfree(ub);
}
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