CVE-2024-26596

In the Linux kernel, the following vulnerability has been resolved: net:
dsa: fix netdev_priv() dereference before check on non-DSA netdevice events
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.