[PATCH AUTOSEL 5.10 13/15] net: vlan: don't propagate flags on open

Sasha Levin
2025-04-03T19:10:33Z

From: Stanislav Fomichev <sdf@fomichev.me>

[ Upstream commit 27b918007d96402aba10ed52a6af8015230f1793 ]

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 allmulticast on down
ip link add name bond1 type bond mode 802.3ad
ip link set dev netdevsim0 down
ip link set dev netdevsim0 master bond1
ip link set dev bond1 up
ip link show

Reported-by: syzbot+b0c03d76056ef6cd12a6@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/Z9CfXjLMKn6VLG5d@mini-arch/T/#m15ba130f53227c883e79fb969687d69d670337a0
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250313100657.2287455-1-sdf@fomichev.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/8021q/vlan_dev.c | 31 ++++---------------------------
1 file changed, 4 insertions(+), 27 deletions(-)

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index b7cf430006e55..c134f8210b21b 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -272,17 +272,6 @@ static int vlan_dev_open(struct net_device *dev)
goto out;
}

- if (dev->flags & IFF_ALLMULTI) {
- err = dev_set_allmulti(real_dev, 1);
- if (err < 0)
- goto del_unicast;
- }
- if (dev->flags & IFF_PROMISC) {
- err = dev_set_promiscuity(real_dev, 1);
- if (err < 0)
- goto clear_allmulti;
- }
-
ether_addr_copy(vlan->real_dev_addr, real_dev->dev_addr);

if (vlan->flags & VLAN_FLAG_GVRP)
@@ -296,12 +285,6 @@ static int vlan_dev_open(struct net_device *dev)
netif_carrier_on(dev);
return 0;

-clear_allmulti:
- if (dev->flags & IFF_ALLMULTI)
- dev_set_allmulti(real_dev, -1);
-del_unicast:
- if (!ether_addr_equal(dev->dev_addr, real_dev->dev_addr))
- dev_uc_del(real_dev, dev->dev_addr);
out:
netif_carrier_off(dev);
return err;
@@ -314,10 +297,6 @@ static int vlan_dev_stop(struct net_device *dev)

dev_mc_unsync(real_dev, dev);
dev_uc_unsync(real_dev, dev);
- if (dev->flags & IFF_ALLMULTI)
- dev_set_allmulti(real_dev, -1);
- if (dev->flags & IFF_PROMISC)
- dev_set_promiscuity(real_dev, -1);

if (!ether_addr_equal(dev->dev_addr, real_dev->dev_addr))
dev_uc_del(real_dev, dev->dev_addr);
@@ -474,12 +453,10 @@ static void vlan_dev_change_rx_flags(struct net_device *dev, int change)
{
struct net_device *real_dev = vlan_dev_priv(dev)->real_dev;

- if (dev->flags & IFF_UP) {
- if (change & IFF_ALLMULTI)
- dev_set_allmulti(real_dev, dev->flags & IFF_ALLMULTI ? 1 : -1);
- if (change & IFF_PROMISC)
- dev_set_promiscuity(real_dev, dev->flags & IFF_PROMISC ? 1 : -1);
- }
+ if (change & IFF_ALLMULTI)
+ dev_set_allmulti(real_dev, dev->flags & IFF_ALLMULTI ? 1 : -1);
+ if (change & IFF_PROMISC)
+ dev_set_promiscuity(real_dev, dev->flags & IFF_PROMISC ? 1 : -1);
}

static void vlan_dev_set_rx_mode(struct net_device *vlan_dev)
--
2.39.5