CVE-2025-68813

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