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 _ipvsgetoutrt() calls dstlinkfailure() without ensuring skb->dev is set, leading to a NULL pointer dereference in fibcomputespecdst() when ipv4linkfailure() attempts to send ICMP destination unreachable messages.

The issue emerged after commit ed0de45a1008 ("ipv4: recompile ip options in ipv4linkfailure") started calling _ipoptionscompile() from ipv4linkfailure(). This code path eventually calls fibcomputespecdst() which dereferences skb->dev. An attempt was made to fix the NULL skb->dev dereference in commit 0113d9c9d1cc ("ipv4: fix null-deref in ipv4linkfailure"), but it only addressed the immediate devnet(skb->dev) dereference by using a fallback device. The fix was incomplete because fibcomputespecdst() later in the call chain still accesses skb->dev directly, which remains NULL when IPVS calls dstlinkfailure().

The crash occurs when: 1. IPVS processes a packet in NAT mode with a misconfigured destination 2. Route lookup fails in __ipvsget_outrt() before establishing a route 3. The error path calls dstlinkfailure(skb) with skb->dev == NULL 4. ipv4linkfailure() → ipv4senddestunreach() → __ipoptionscompile() → fibcomputespecdst() 5. fibcomputespecdst() dereferences NULL skb->dev

Apply the same fix used for IPv6 in commit 326bf17ea5d4 ("ipvs: fix ipv6 route unreach panic"): set skb->dev from skbdst(skb)->dev before calling dstlink_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:__indevget_rcu include/linux/inetdevice.h:233 RIP: 0010:fibcomputespecdst+0x17a/0x9f0 net/ipv4/fibfrontend.c:285 Call Trace: <TASK> specdstfill net/ipv4/ipoptions.c:232 specdstfill net/ipv4/ipoptions.c:229 __ipoptionscompile+0x13a1/0x17d0 net/ipv4/ipoptions.c:330 ipv4senddestunreach net/ipv4/route.c:1252 ipv4linkfailure+0x702/0xb80 net/ipv4/route.c:1265 dstlinkfailure include/net/dst.h:437 _ipvsgetoutrt+0x15fd/0x19e0 net/netfilter/ipvs/ipvsxmit.c:412 ipvsnatxmit+0x1d8/0xc80 net/netfilter/ipvs/ipvsxmit.c:764