CVE-2024-26596

net: dsa: fix netdev_priv() dereference before check on non-DSA netdevice events

Published Feb 23, 2024 CVSS 3.1 · 5.5 Medium EPSS < 1% KEV · Not listed
Description
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.

Analysis

No analysis available yet

Remediation

No remediation available yet

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4102-1 linux-6.1 security update
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 15, 2026, 12:38 AM
Reserved
Feb 19, 2024, 2:20 PM
Status
Modified
Published
Feb 23, 2024, 3:15 PM
Modified
Jun 17, 2026, 7:17 AM