net: Fix ip link add netns oops

Ed Swierk <eswierk@bigswitch.com> writes:
> On 2.6.35.7
>  ip link add link eth0 netns 9999 type macvlan
> where 9999 is a nonexistent PID triggers an oops and causes all network functions to hang:
> [10663.821898] BUG: unable to handle kernel NULL pointer dereference at 000000000000006d
>  [10663.821917] IP: [<ffffffff8149c2fa>] __dev_alloc_name+0x9a/0x170
>  [10663.821933] PGD 1d3927067 PUD 22f5c5067 PMD 0
>  [10663.821944] Oops: 0000 [#1] SMP
>  [10663.821953] last sysfs file: /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
>  [10663.821959] CPU 3
>  [10663.821963] Modules linked in: macvlan ip6table_filter ip6_tables rfcomm ipt_MASQUERADE binfmt_misc iptable_nat nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack sco ipt_REJECT bnep l2cap xt_tcpudp iptable_filter ip_tables x_tables bridge stp vboxnetadp vboxnetflt vboxdrv kvm_intel kvm parport_pc ppdev snd_hda_codec_intelhdmi snd_hda_codec_conexant arc4 iwlagn iwlcore mac80211 snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq_midi snd_rawmidi i915 snd_seq_midi_event snd_seq thinkpad_acpi drm_kms_helper btusb tpm_tis nvram uvcvideo snd_timer snd_seq_device bluetooth videodev v4l1_compat v4l2_compat_ioctl32 tpm drm tpm_bios snd cfg80211 psmouse serio_raw intel_ips soundcore snd_page_alloc intel_agp i2c_algo_bit video output netconsole configfs lp parport usbhid hid e1000e sdhci_pci ahci libahci sdhci led_class
>  [10663.822155]
>  [10663.822161] Pid: 6000, comm: ip Not tainted 2.6.35-23-generic #41-Ubuntu 2901CTO/2901CTO
>  [10663.822167] RIP: 0010:[<ffffffff8149c2fa>] [<ffffffff8149c2fa>] __dev_alloc_name+0x9a/0x170
>  [10663.822177] RSP: 0018:ffff88014aebf7b8 EFLAGS: 00010286
>  [10663.822182] RAX: 00000000fffffff4 RBX: ffff8801ad900800 RCX: 0000000000000000
>  [10663.822187] RDX: ffff880000000000 RSI: 0000000000000000 RDI: ffff88014ad63000
>  [10663.822191] RBP: ffff88014aebf808 R08: 0000000000000041 R09: 0000000000000041
>  [10663.822196] R10: 0000000000000000 R11: dead000000200200 R12: ffff88014aebf818
>  [10663.822201] R13: fffffffffffffffd R14: ffff88014aebf918 R15: ffff88014ad62000
>  [10663.822207] FS: 00007f00c487f700(0000) GS:ffff880001f80000(0000) knlGS:0000000000000000
>  [10663.822212] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  [10663.822216] CR2: 000000000000006d CR3: 0000000231f19000 CR4: 00000000000026e0
>  [10663.822221] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  [10663.822226] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>  [10663.822231] Process ip (pid: 6000, threadinfo ffff88014aebe000, task ffff88014afb16e0)
>  [10663.822236] Stack:
>  [10663.822240] ffff88014aebf808 ffffffff814a2bb5 ffff88014aebf7e8 00000000a00ee8d6
>  [10663.822251] <0> 0000000000000000 ffffffffa00ef940 ffff8801ad900800 ffff88014aebf818
>  [10663.822265] <0> ffff88014aebf918 ffff8801ad900800 ffff88014aebf858 ffffffff8149c413
>  [10663.822281] Call Trace:
>  [10663.822290] [<ffffffff814a2bb5>] ? dev_addr_init+0x75/0xb0
>  [10663.822298] [<ffffffff8149c413>] dev_alloc_name+0x43/0x90
>  [10663.822307] [<ffffffff814a85ee>] rtnl_create_link+0xbe/0x1b0
>  [10663.822314] [<ffffffff814ab2aa>] rtnl_newlink+0x48a/0x570
>  [10663.822321] [<ffffffff814aafcc>] ? rtnl_newlink+0x1ac/0x570
>  [10663.822332] [<ffffffff81030064>] ? native_x2apic_icr_read+0x4/0x20
>  [10663.822339] [<ffffffff814a8c17>] rtnetlink_rcv_msg+0x177/0x290
>  [10663.822346] [<ffffffff814a8aa0>] ? rtnetlink_rcv_msg+0x0/0x290
>  [10663.822354] [<ffffffff814c25d9>] netlink_rcv_skb+0xa9/0xd0
>  [10663.822360] [<ffffffff814a8a85>] rtnetlink_rcv+0x25/0x40
>  [10663.822367] [<ffffffff814c223e>] netlink_unicast+0x2de/0x2f0
>  [10663.822374] [<ffffffff814c303e>] netlink_sendmsg+0x1fe/0x2e0
>  [10663.822383] [<ffffffff81488533>] sock_sendmsg+0xf3/0x120
>  [10663.822391] [<ffffffff815899fe>] ? _raw_spin_lock+0xe/0x20
>  [10663.822400] [<ffffffff81168656>] ? __d_lookup+0x136/0x150
>  [10663.822406] [<ffffffff815899fe>] ? _raw_spin_lock+0xe/0x20
>  [10663.822414] [<ffffffff812b7a0d>] ? _atomic_dec_and_lock+0x4d/0x80
>  [10663.822422] [<ffffffff8116ea90>] ? mntput_no_expire+0x30/0x110
>  [10663.822429] [<ffffffff81486ff5>] ? move_addr_to_kernel+0x65/0x70
>  [10663.822435] [<ffffffff81493308>] ? verify_iovec+0x88/0xe0
>  [10663.822442] [<ffffffff81489020>] sys_sendmsg+0x240/0x3a0
> [10663.822450] [<ffffffff8111e2a9>] ? __do_fault+0x479/0x560
>  [10663.822457] [<ffffffff815899fe>] ? _raw_spin_lock+0xe/0x20
>  [10663.822465] [<ffffffff8116cf4a>] ? alloc_fd+0x10a/0x150
>  [10663.822473] [<ffffffff8158d76e>] ? do_page_fault+0x15e/0x350
>  [10663.822482] [<ffffffff8100a0f2>] system_call_fastpath+0x16/0x1b
>  [10663.822487] Code: 90 48 8d 78 02 be 25 00 00 00 e8 92 1d e2 ff 48 85 c0 75 cf bf 20 00 00 00 e8 c3 b1 c6 ff 49 89 c7 b8 f4 ff ff ff 4d 85 ff 74 bd <4d> 8b 75 70 49 8d 45 70 48 89 45 b8 49 83 ee 58 eb 28 48 8d 55
>  [10663.822618] RIP [<ffffffff8149c2fa>] __dev_alloc_name+0x9a/0x170
>  [10663.822627] RSP <ffff88014aebf7b8>
>  [10663.822631] CR2: 000000000000006d
>  [10663.822636] ---[ end trace 3dfd6c3ad5327ca7 ]---

This bug was introduced in:
commit 81adee47dfb608df3ad0b91d230fb3cef75f0060
Author: Eric W. Biederman <ebiederm@aristanetworks.com>
Date:   Sun Nov 8 00:53:51 2009 -0800

    net: Support specifying the network namespace upon device creation.

    There is no good reason to not support userspace specifying the
    network namespace during device creation, and it makes it easier
    to create a network device and pass it to a child network namespace
    with a well known name.

    We have to be careful to ensure that the target network namespace
    for the new device exists through the life of the call.  To keep
    that logic clear I have factored out the network namespace grabbing
    logic into rtnl_link_get_net.

    In addtion we need to continue to pass the source network namespace
    to the rtnl_link_ops.newlink method so that we can find the base
    device source network namespace.

    Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
    Acked-by: Eric Dumazet <eric.dumazet@gmail.com>

Where apparently I forgot to add error handling to the path where we create
a new network device in a new network namespace, and pass in an invalid pid.

Cc: stable@kernel.org
Reported-by: Ed Swierk <eswierk@bigswitch.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -1671,6 +1671,9 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 			snprintf(ifname, IFNAMSIZ, "%s%%d", ops->kind);
 
 		dest_net = rtnl_link_get_net(net, tb);
+		if (IS_ERR(dest_net))
+			return PTR_ERR(dest_net);
+
 		dev = rtnl_create_link(net, dest_net, ifname, ops, tb);
 
 		if (IS_ERR(dev))