HIGH
ipvs Route NullDeref
CVE-2025-68813
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
01Description
In the Linux kernel, the following vulnerability has been resolved: ipvs: fix ipv4 null-ptr-deref in route error path The IPv4 code path in __ip_vs_get_out_rt() calls dst_link_failure() without ensuring skb->dev is set, leading to a NULL pointer dereference in fib_compute_spec_dst() when ipv4_link_failure() attempts to send ICMP destination unreachable messages. The issue emerged after commit ed0de45a1008 ("ipv4: recompile ip options in ipv4_link_failure") started calling __ip_options_compile() from ipv4_link_failure(). This code path eventually calls fib_compute_spec_dst() which dereferences skb->dev. An attempt was made to fix the NULL skb->dev dereference in commit 0113d9c9d1cc ("ipv4: fix null-deref in ipv4_link_failure"), but it only addressed the immediate dev_net(skb->dev) dereference by using a fallback device. The fix was incomplete because fib_compute_spec_dst() later in the call chain still accesses skb->dev directly, which remains NULL when IPVS calls dst_link_failure(). The crash occurs when: 1. IPVS processes a packet in NAT mode with a misconfigured destination 2. Route lookup fails in __ip_vs_get_out_rt() before establishing a route 3. The error path calls dst_link_failure(skb) with skb->dev == NULL 4. ipv4_link_failure() → ipv4_send_dest_unreach() → __ip_options_compile() → fib_compute_spec_dst() 5. fib_compute_spec_dst() dereferences NULL skb->dev Apply the same fix used for IPv6 in commit 326bf17ea5d4 ("ipvs: fix ipv6 route unreach panic"): set skb->dev from skb_dst(skb)->dev before calling dst_link_failure(). KASAN: null-ptr-deref in range [0x0000000000000328-0x000000000000032f] CPU: 1 PID: 12732 Comm: syz.1.3469 Not tainted 6.6.114 #2 RIP: 0010:__in_dev_get_rcu include/linux/inetdevice.h:233 RIP: 0010:fib_compute_spec_dst+0x17a/0x9f0 net/ipv4/fib_frontend.c:285 Call Trace: <TASK> spec_dst_fill net/ipv4/ip_options.c:232 spec_dst_fill net/ipv4/ip_options.c:229 __ip_options_compile+0x13a1/0x17d0 net/ipv4/ip_options.c:330 ipv4_send_dest_unreach net/ipv4/route.c:1252 ipv4_link_failure+0x702/0xb80 net/ipv4/route.c:1265 dst_link_failure include/net/dst.h:437 __ip_vs_get_out_rt+0x15fd/0x19e0 net/netfilter/ipvs/ip_vs_xmit.c:412 ip_vs_nat_xmit+0x1d8/0xc80 net/netfilter/ipvs/ip_vs_xmit.c:764
02KernelScan AI Analysis
Risk summary
Systems using IPVS IPv4 load balancing with misconfigured NAT destinations are vulnerable to remote denial-of-service. A network packet sent to the affected virtual service triggers a NULL pointer dereference in the kernel's IPv4 route error path, resulting in a kernel panic. No authentication or local access is required to exploit the vulnerability once the misconfigured destination exists.
Vulnerability analysis
The root cause is that __ip_vs_get_out_rt() calls dst_link_failure() in the route error path without ensuring skb->dev is set. When IPVS NAT mode forwards a packet to a misconfigured backend and route lookup fails, the error handling code attempts to send an ICMP destination unreachable message via ipv4_link_failure(). This eventually calls fib_compute_spec_dst(), which dereferences the NULL skb->dev pointer. The fix sets skb->dev from the destination route before calling dst_link_failure(), mirroring the IPv6 fix. The bug is reachable remotely by any network client that can send traffic to the affected IPVS service.
03Fix Versions
| Branch | Fixed in | Patch commit |
|---|---|---|
| 3.19 | 3.19 | dd72a93c8040 |
| 4.10 | 4.10 | cdeff10851c3 |
| 4.15 | 4.15 | 4729ff0581fb |
| 4.20 | 4.20 | 25ab24df31f7 |
| 4.5 | 4.5 | 312d7cd88882 |
| 5.1 | 5.1 | 689a627d1478 |
| 5.10 | 5.10.248 | ad891bb3d079 |
| 5.15 | 5.15.198 | — |
| 6.1 | 6.1.160 | — |
| 6.12 | 6.12.64 | — |
| 6.18 | 6.18.3 | — |
| 6.6 | 6.6.120 | — |
| mainline | 6.19 | — |