net: vlan: don't propagate flags on open

In the Linux kernel, the following vulnerability has been resolved:

net: vlan: don't propagate flags on open

With the device instance lock, there is now a possibility of a deadlock:

[ 1.211455] ============================================

[ 1.211571] WARNING: possible recursive locking detected

[ 1.211687] 6.14.0-rc5-01215-g032756b4ca7a-dirty #5 Not tainted

[ 1.211823] --------------------------------------------

[ 1.211936] ip/184 is trying to acquire lock:

[ 1.212032] ffff8881024a4c30 (&dev->lock){+.+.}-{4:4}, at: dev_set_allmulti+0x4e/0xb0

[ 1.212207]

[ 1.212207] but task is already holding lock:

[ 1.212332] ffff8881024a4c30 (&dev->lock){+.+.}-{4:4}, at: dev_open+0x50/0xb0

[ 1.212487]

[ 1.212487] other info that might help us debug this:

[ 1.212626] Possible unsafe locking scenario:

[ 1.212626]

[ 1.212751] CPU0

[ 1.212815] ----

[ 1.212871] lock(&dev->lock);

[ 1.212944] lock(&dev->lock);

[ 1.213016]

[ 1.213016] *** DEADLOCK ***

[ 1.213016]

[ 1.213143] May be due to missing lock nesting notation

[ 1.213143]

[ 1.213294] 3 locks held by ip/184:

[ 1.213371] #0: ffffffff838b53e0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock+0x1b/0xa0

[ 1.213543] #1: ffffffff84e5fc70 (&net->rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock+0x37/0xa0

[ 1.213727] #2: ffff8881024a4c30 (&dev->lock){+.+.}-{4:4}, at: dev_open+0x50/0xb0

[ 1.213895]

[ 1.213895] stack backtrace:

[ 1.213991] CPU: 0 UID: 0 PID: 184 Comm: ip Not tainted 6.14.0-rc5-01215-g032756b4ca7a-dirty #5

[ 1.213993] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014

[ 1.213994] Call Trace:

[ 1.213995] <TASK>

[ 1.213996] dump_stack_lvl+0x8e/0xd0

[ 1.214000] print_deadlock_bug+0x28b/0x2a0

[ 1.214020] lock_acquire+0xea/0x2a0

[ 1.214027] __mutex_lock+0xbf/0xd40

[ 1.214038] dev_set_allmulti+0x4e/0xb0 # real_dev->flags & IFF_ALLMULTI

[ 1.214040] vlan_dev_open+0xa5/0x170 # ndo_open on vlandev

[ 1.214042] __dev_open+0x145/0x270

[ 1.214046] __dev_change_flags+0xb0/0x1e0

[ 1.214051] netif_change_flags+0x22/0x60 # IFF_UP vlandev

[ 1.214053] dev_change_flags+0x61/0xb0 # for each device in group from dev->vlan_info

[ 1.214055] vlan_device_event+0x766/0x7c0 # on netdevsim0

[ 1.214058] notifier_call_chain+0x78/0x120

[ 1.214062] netif_open+0x6d/0x90

[ 1.214064] dev_open+0x5b/0xb0 # locks netdevsim0

[ 1.214066] bond_enslave+0x64c/0x1230

[ 1.214075] do_set_master+0x175/0x1e0 # on netdevsim0

[ 1.214077] do_setlink+0x516/0x13b0

[ 1.214094] rtnl_newlink+0xaba/0xb80

[ 1.214132] rtnetlink_rcv_msg+0x440/0x490

[ 1.214144] netlink_rcv_skb+0xeb/0x120

[ 1.214150] netlink_unicast+0x1f9/0x320

[ 1.214153] netlink_sendmsg+0x346/0x3f0

[ 1.214157] __sock_sendmsg+0x86/0xb0

[ 1.214160] ____sys_sendmsg+0x1c8/0x220

[ 1.214164] ___sys_sendmsg+0x28f/0x2d0

[ 1.214179] __x64_sys_sendmsg+0xef/0x140

[ 1.214184] do_syscall_64+0xec/0x1d0

[ 1.214190] entry_SYSCALL_64_after_hwframe+0x77/0x7f

[ 1.214191] RIP: 0033:0x7f2d1b4a7e56

Device setup:

netdevsim0 (down)

^ ^

bond netdevsim1.100@netdevsim1 allmulticast=on (down)

When we enslave the lower device (netdevsim0) which has a vlan, we

propagate vlan's allmuti/promisc flags during ndo_open. This causes

(re)locking on of the real_dev.

Propagate allmulti/promisc on flags change, not on the open. There

is a slight semantics change that vlans that are down now propagate

the flags, but this seems unlikely to result in the real issues.

Reproducer:

echo 0 1 > /sys/bus/netdevsim/new_device

dev_path=$(ls -d /sys/bus/netdevsim/devices/netdevsim0/net/*)

dev=$(echo $dev_path | rev | cut -d/ -f1 | rev)

ip link set dev $dev name netdevsim0

ip link set dev netdevsim0 up

ip link add link netdevsim0 name netdevsim0.100 type vlan id 100

ip link set dev netdevsim0.100 allm

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