CVE-2026-23398

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

icmp: fix NULL pointer dereference in icmp_tag_validation()

icmp_tag_validation() unconditionally dereferences the result of

rcu_dereference(inet_protos[proto]) without checking for NULL.

The inet_protos[] array is sparse -- only about 15 of 256 protocol

numbers have registered handlers. When ip_no_pmtu_disc is set to 3

(hardened PMTU mode) and the kernel receives an ICMP Fragmentation

Needed error with a quoted inner IP header containing an unregistered

protocol number, the NULL dereference causes a kernel panic in

softirq context.

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN NOPTI

KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]

RIP: 0010:icmp_unreach (net/ipv4/icmp.c:1085 net/ipv4/icmp.c:1143)

Call Trace:

<IRQ>

icmp_rcv (net/ipv4/icmp.c:1527)

ip_protocol_deliver_rcu (net/ipv4/ip_input.c:207)

ip_local_deliver_finish (net/ipv4/ip_input.c:242)

ip_local_deliver (net/ipv4/ip_input.c:262)

ip_rcv (net/ipv4/ip_input.c:573)

__netif_receive_skb_one_core (net/core/dev.c:6164)

process_backlog (net/core/dev.c:6628)

handle_softirqs (kernel/softirq.c:561)

</IRQ>

Add a NULL check before accessing icmp_strict_tag_validation. If the

protocol has no registered handler, return false since it cannot

perform strict tag validation.