Bug 2401525 (CVE-2023-53600)

Summary: CVE-2023-53600 kernel: tunnels: fix kasan splat when generating ipv4 pmtu error
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel in which a checksum calculating function improperly handled nonlinear skbs, resulting in a possible denial of service or disclosure of kernel memory. Because of the challenge of controlling this behavior, the impact of this flaw is limited.
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Description OSIDB Bzimport 2025-10-04 16:05:36 UTC 
In the Linux kernel, the following vulnerability has been resolved:

tunnels: fix kasan splat when generating ipv4 pmtu error

If we try to emit an icmp error in response to a nonliner skb, we get

BUG: KASAN: slab-out-of-bounds in ip_compute_csum+0x134/0x220
Read of size 4 at addr ffff88811c50db00 by task iperf3/1691
CPU: 2 PID: 1691 Comm: iperf3 Not tainted 6.5.0-rc3+ #309
[..]
 kasan_report+0x105/0x140
 ip_compute_csum+0x134/0x220
 iptunnel_pmtud_build_icmp+0x554/0x1020
 skb_tunnel_check_pmtu+0x513/0xb80
 vxlan_xmit_one+0x139e/0x2ef0
 vxlan_xmit+0x1867/0x2760
 dev_hard_start_xmit+0x1ee/0x4f0
 br_dev_queue_push_xmit+0x4d1/0x660
 [..]

ip_compute_csum() cannot deal with nonlinear skbs, so avoid it.
After this change, splat is gone and iperf3 is no longer stuck.
Comment 1 Alexander B 2025-10-06 13:53:17 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025100430-CVE-2023-53600-69ba@gregkh/T