Description

In the Linux kernel, the following vulnerability has been resolved:

nsh: Restore skb->{protocol,data,mac_header} for outer header in nsh_gso_segment().

syzbot triggered various splats (see [0] and links) by a crafted GSO
packet of VIRTIO_NET_HDR_GSO_UDP layering the following protocols:

ETH_P_8021AD + ETH_P_NSH + ETH_P_IPV6 + IPPROTO_UDP

NSH can encapsulate IPv4, IPv6, Ethernet, NSH, and MPLS. As the inner
protocol can be Ethernet, NSH GSO handler, nsh_gso_segment(), calls
skb_mac_gso_segment() to invoke inner protocol GSO handlers.

nsh_gso_segment() does the following for the original skb before
calling skb_mac_gso_segment()

1. reset skb->network_header
2. save the original skb->{mac_heaeder,mac_len} in a local variable
3. pull the NSH header
4. resets skb->mac_header
5. set up skb->mac_len and skb->protocol for the inner protocol.

and does the following for the segmented skb

6. set ntohs(ETH_P_NSH) to skb->protocol
7. push the NSH header
8. restore skb->mac_header
9. set skb->mac_header + mac_len to skb->network_header
10. restore skb->mac_len

There are two problems in 6-7 and 8-9.

(a)
After 6 & 7, skb->data points to the NSH header, so the outer header
(ETH_P_8021AD in this case) is stripped when skb is sent out of netdev.

Also, if NSH is encapsulated by NSH + Ethernet (so NSH-Ethernet-NSH),
skb_pull() in the first nsh_gso_segment() will make skb->data point
to the middle of the outer NSH or Ethernet header because the Ethern...

Classification

CVE ID: CVE-2024-36933

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 15.26% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/a7c2c3c1caabcb4a3d6c47284c397507aaf54fe9
https://git.kernel.org/stable/c/46134031c20fd313d03b90169d64b2e05ca6b65c
https://git.kernel.org/stable/c/bbccf0caef2fa917d6d0692385a06ce3c262a216
https://git.kernel.org/stable/c/5a4603fbc285752d19e4b415466db18ef3617e4a
https://git.kernel.org/stable/c/37ed6f244ec5bda2e90b085084e322ea55d0aaa2
https://git.kernel.org/stable/c/696d18bb59727a2e0526c0802a812620be1c9340
https://git.kernel.org/stable/c/29a07f2ee4d273760c2acbfc756e29eccd82470a
https://git.kernel.org/stable/c/4b911a9690d72641879ea6d13cce1de31d346d79

Timeline