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Date: Thu, 22 Jul 2021 11:53:37 +0200
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Ziyang Xuan <william.xuanziyang@...wei.com>
Cc: mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
linux-can@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] can: raw: fix raw_rcv panic for sock UAF
On 22.07.21 09:08, Ziyang Xuan wrote:
> We get a bug during ltp can_filter test as following.
>
> ===========================================
> [60919.264984] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
> [60919.265223] PGD 8000003dda726067 P4D 8000003dda726067 PUD 3dda727067 PMD 0
> [60919.265443] Oops: 0000 [#1] SMP PTI
> [60919.265550] CPU: 30 PID: 3638365 Comm: can_filter Kdump: loaded Tainted: G W 4.19.90+ #1
> [60919.266068] RIP: 0010:selinux_socket_sock_rcv_skb+0x3e/0x200
> [60919.293289] RSP: 0018:ffff8d53bfc03cf8 EFLAGS: 00010246
> [60919.307140] RAX: 0000000000000000 RBX: 000000000000001d RCX: 0000000000000007
> [60919.320756] RDX: 0000000000000001 RSI: ffff8d5104a8ed00 RDI: ffff8d53bfc03d30
> [60919.334319] RBP: ffff8d9338056800 R08: ffff8d53bfc29d80 R09: 0000000000000001
> [60919.347969] R10: ffff8d53bfc03ec0 R11: ffffb8526ef47c98 R12: ffff8d53bfc03d30
> [60919.350320] perf: interrupt took too long (3063 > 2500), lowering kernel.perf_event_max_sample_rate to 65000
> [60919.361148] R13: 0000000000000001 R14: ffff8d53bcf90000 R15: 0000000000000000
> [60919.361151] FS: 00007fb78b6b3600(0000) GS:ffff8d53bfc00000(0000) knlGS:0000000000000000
> [60919.400812] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [60919.413730] CR2: 0000000000000010 CR3: 0000003e3f784006 CR4: 00000000007606e0
> [60919.426479] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [60919.439339] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [60919.451608] PKRU: 55555554
> [60919.463622] Call Trace:
> [60919.475617] <IRQ>
> [60919.487122] ? update_load_avg+0x89/0x5d0
> [60919.498478] ? update_load_avg+0x89/0x5d0
> [60919.509822] ? account_entity_enqueue+0xc5/0xf0
> [60919.520709] security_sock_rcv_skb+0x2a/0x40
> [60919.531413] sk_filter_trim_cap+0x47/0x1b0
> [60919.542178] ? kmem_cache_alloc+0x38/0x1b0
> [60919.552444] sock_queue_rcv_skb+0x17/0x30
> [60919.562477] raw_rcv+0x110/0x190 [can_raw]
> [60919.572539] can_rcv_filter+0xbc/0x1b0 [can]
> [60919.582173] can_receive+0x6b/0xb0 [can]
> [60919.591595] can_rcv+0x31/0x70 [can]
> [60919.600783] __netif_receive_skb_one_core+0x5a/0x80
> [60919.609864] process_backlog+0x9b/0x150
> [60919.618691] net_rx_action+0x156/0x400
> [60919.627310] ? sched_clock_cpu+0xc/0xa0
> [60919.635714] __do_softirq+0xe8/0x2e9
> [60919.644161] do_softirq_own_stack+0x2a/0x40
> [60919.652154] </IRQ>
> [60919.659899] do_softirq.part.17+0x4f/0x60
> [60919.667475] __local_bh_enable_ip+0x60/0x70
> [60919.675089] __dev_queue_xmit+0x539/0x920
> [60919.682267] ? finish_wait+0x80/0x80
> [60919.689218] ? finish_wait+0x80/0x80
> [60919.695886] ? sock_alloc_send_pskb+0x211/0x230
> [60919.702395] ? can_send+0xe5/0x1f0 [can]
> [60919.708882] can_send+0xe5/0x1f0 [can]
> [60919.715037] raw_sendmsg+0x16d/0x268 [can_raw]
>
> It's because raw_setsockopt() concurrently with
> unregister_netdevice_many(). Concurrent scenario as following.
>
> cpu0 cpu1
> raw_bind
> raw_setsockopt unregister_netdevice_many
> unlist_netdevice
> dev_get_by_index raw_notifier
> raw_enable_filters ......
> can_rx_register
> can_rcv_list_find(..., net->can.rx_alldev_list)
>
> ......
>
> sock_close
> raw_release(sock_a)
>
> ......
>
> can_receive
> can_rcv_filter(net->can.rx_alldev_list, ...)
> raw_rcv(skb, sock_a)
> BUG
>
> After unlist_netdevice(), dev_get_by_index() return NULL in
> raw_setsockopt(). Function raw_enable_filters() will add sock
> and can_filter to net->can.rx_alldev_list. Then the sock is closed.
> Followed by, we sock_sendmsg() to a new vcan device use the same
> can_filter. Protocol stack match the old receiver whose sock has
> been released on net->can.rx_alldev_list in can_rcv_filter().
> Function raw_rcv() uses the freed sock. UAF BUG is triggered.
>
> We can find that the key issue is that net_device has not been
> protected in raw_setsockopt(). Use rtnl_lock to protect net_device
> in raw_setsockopt().
>
> Fixes: c18ce101f2e4 ("[CAN]: Add raw protocol")
> Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
> ---
> v2:
> - add exception handling for dev_get_by_index return NULL
> net/can/raw.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/net/can/raw.c b/net/can/raw.c
> index ed4fcb7ab0c3..cd5a49380116 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -546,10 +546,18 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> return -EFAULT;
> }
>
> + rtnl_lock();
> lock_sock(sk);
>
> - if (ro->bound && ro->ifindex)
> + if (ro->bound && ro->ifindex) {
> dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> + if (!dev) {
> + if (count > 1)
> + kfree(filter);
This was NOT suggested!
I've been talking about removing the other kfree() "improvement" you
suggested.
The kfree() should only be done when ro->bound and ro->ifindex are cleared.
So when you remove these two lines it should be ok.
Please try to increase the context in the diff.
Thanks,
Oliver
> + err = -ENODEV;
> + goto out_fil;
> + }
> + }
>
> if (ro->bound) {
> /* (try to) register the new filters */
> @@ -588,6 +596,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> dev_put(dev);
>
> release_sock(sk);
> + rtnl_unlock();
>
> break;
>
> @@ -600,10 +609,16 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>
> err_mask &= CAN_ERR_MASK;
>
> + rtnl_lock();
> lock_sock(sk);
>
> - if (ro->bound && ro->ifindex)
> + if (ro->bound && ro->ifindex) {
> dev = dev_get_by_index(sock_net(sk), ro->ifindex);
> + if (!dev) {
> + err = -ENODEV;
> + goto out_err;
> + }
> + }
>
> /* remove current error mask */
> if (ro->bound) {
> @@ -627,6 +642,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
> dev_put(dev);
>
> release_sock(sk);
> + rtnl_unlock();
>
> break;
>
>
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