From: Vladimir Oltean vladimir.oltean@nxp.com

commit 844f104790bd69c2e4dbb9ee3eba46fde1fcea7b upstream.

After the blamed commit, we started doing this dereference for every NETDEV_CHANGEUPPER and NETDEV_PRECHANGEUPPER event in the system.

static inline struct dsa_port *dsa_user_to_port(const struct net_device *dev) { struct dsa_user_priv *p = netdev_priv(dev);

return p->dp; }

Which is obviously bogus, because not all net_devices have a netdev_priv() of type struct dsa_user_priv. But struct dsa_user_priv is fairly small, and p->dp means dereferencing 8 bytes starting with offset 16. Most drivers allocate that much private memory anyway, making our access not fault, and we discard the bogus data quickly afterwards, so this wasn't caught.

But the dummy interface is somewhat special in that it calls alloc_netdev() with a priv size of 0. So every netdev_priv() dereference is invalid, and we get this when we emit a NETDEV_PRECHANGEUPPER event with a VLAN as its new upper:

$ ip link add dummy1 type dummy $ ip link add link dummy1 name dummy1.100 type vlan id 100 [ 43.309174] ================================================================== [ 43.316456] BUG: KASAN: slab-out-of-bounds in dsa_user_prechangeupper+0x30/0xe8 [ 43.323835] Read of size 8 at addr ffff3f86481d2990 by task ip/374 [ 43.330058] [ 43.342436] Call trace: [ 43.366542] dsa_user_prechangeupper+0x30/0xe8 [ 43.371024] dsa_user_netdevice_event+0xb38/0xee8 [ 43.375768] notifier_call_chain+0xa4/0x210 [ 43.379985] raw_notifier_call_chain+0x24/0x38 [ 43.384464] __netdev_upper_dev_link+0x3ec/0x5d8 [ 43.389120] netdev_upper_dev_link+0x70/0xa8 [ 43.393424] register_vlan_dev+0x1bc/0x310 [ 43.397554] vlan_newlink+0x210/0x248 [ 43.401247] rtnl_newlink+0x9fc/0xe30 [ 43.404942] rtnetlink_rcv_msg+0x378/0x580

Avoid the kernel oops by dereferencing after the type check, as customary.

Fixes: 4c3f80d22b2e ("net: dsa: walk through all changeupper notifier functions") Reported-and-tested-by: syzbot+d81bcd883824180500c8@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/0000000000001d4255060e87545c@google.com/ Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Reviewed-by: Florian Fainelli florian.fainelli@broadcom.com Reviewed-by: Eric Dumazet edumazet@google.com Link: https://lore.kernel.org/r/20240110003354.2796778-1-vladimir.oltean@nxp.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Wenshan Lan jetlan9@163.com --- v2: add the upstream commit in this commit log. --- net/dsa/slave.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c index 5fe075bf479e..caeb7e75b287 100644 --- a/net/dsa/slave.c +++ b/net/dsa/slave.c @@ -2592,13 +2592,14 @@ EXPORT_SYMBOL_GPL(dsa_slave_dev_check); static int dsa_slave_changeupper(struct net_device *dev, struct netdev_notifier_changeupper_info *info) { - struct dsa_port *dp = dsa_slave_to_port(dev); struct netlink_ext_ack *extack; int err = NOTIFY_DONE; + struct dsa_port *dp;

if (!dsa_slave_dev_check(dev)) return err;

+ dp = dsa_slave_to_port(dev); extack = netdev_notifier_info_to_extack(&info->info);

if (netif_is_bridge_master(info->upper_dev)) { @@ -2652,11 +2653,13 @@ static int dsa_slave_changeupper(struct net_device *dev, static int dsa_slave_prechangeupper(struct net_device *dev, struct netdev_notifier_changeupper_info *info) { - struct dsa_port *dp = dsa_slave_to_port(dev); + struct dsa_port *dp;

if (!dsa_slave_dev_check(dev)) return NOTIFY_DONE;

+ dp = dsa_slave_to_port(dev); + if (netif_is_bridge_master(info->upper_dev) && !info->linking) dsa_port_pre_bridge_leave(dp, info->upper_dev); else if (netif_is_lag_master(info->upper_dev) && !info->linking)