CVE-2026-98303

Summary

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

ipv4: icmp: reject RTN_UNREACHABLE input routes in icmp_route_lookup

When the forward output route cannot be used in icmp_route_lookup(), it enters the "reverse path" and calls ip_route_input() on fl4_dec.daddr, the original packet's source address.

ip_route_input() only returns an error for truly invalid packets. For unreachable addresses it will succeed and return an input route whose dst.output is set to ip_rt_bug(). The existing check only rejects RTN_LOCAL routes, so the RTN_UNREACHABLE route types can still be returned and later used for output, syzkaller triggering a WARN_ON_ONCE() in ip_rt_bug() as bellow:

————[ cut here ]———— WARNING: net/ipv4/route.c:1273 at ip_rt_bug+0x14/0x20 RIP: 0010:ip_rt_bug+0x14/0x20 Call Trace: ip_push_pending_frames+0xfa/0x100 __icmp_send+0x905/0xf10 ip_options_compile+0xc0/0xd0 ip_rcv_finish_core+0x321/0xae0 ip_rcv+0x1de/0x260 __netif_receive_skb_one_core+0x11a/0x130 netif_receive_skb+0x7b/0x260 tun_get_user+0x11bf/0x1c10 ————[ cut here ]————

Reject input route that is RTN_UNREACHABLE to fix it. The net warning is only printed for RTN_LOCAL, as RTN_UNREACHABLE is not the result of a race condition.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/06083cea4a3b95f5ebc85312f97d7086e6c9e782
• https://git.kernel.org/stable/c/83aa83f81a8fec30ff5372dee60b2f0561bcb2ca
• https://git.kernel.org/stable/c/cac69c50716c712ef0114837c9427da66066124c
• https://git.kernel.org/stable/c/1af2d87964d87ba7626d96928d68c09158b5a223
• https://git.kernel.org/stable/c/fda3000147dc96c75ba162f680bec0a9fecf3037
• https://git.kernel.org/stable/c/2998147b59c9df0a51477c7a6b3d1f0ba3127dd4

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