ipvs: fix ipv4 null-ptr-deref in route error path

Overview

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

Affected

• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < dd72a93c80408f06327dd2d956eb1a656d0b5903
• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < 312d7cd88882fc6cadcc08b02287497aaaf94bcd
• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < cdeff10851c37a002d87a035818ebd60fdb74447
• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < 4729ff0581fbb7ad098b6153b76b6f5aac94618a
• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < 25ab24df31f7af843c96a38e0781b9165216e1a8
• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < 689a627d14788ad772e0fa24c2e57a23dbc7ce90
• Linux >= ed0de45a1008991fdaa27a0152befcb74d126a8b < ad891bb3d079a46a821bf2b8867854645191bab0
• Linux 6c2fa855d8178699706b1192db2f1f8102b0ba1e
• Linux fbf569d2beee2a4a7a0bc8b619c26101d1211a88
• Linux ff71f99d5fb2daf54340e8b290d0bc4e6b4c1d38
• Linux 3d988fcddbe7b8673a231958bd2fba61b5a7ced9
• Linux 8a430e56a6485267a1b2d3747209d26c54d1a34b
• Linux 6bd1ee0a993fc9574ae43c1994c54a60cb23a380
• Linux >= 3.18.139 < 3.19
• Linux >= 4.4.179 < 4.5
• Linux >= 4.9.171 < 4.10
• Linux >= 4.14.114 < 4.15
• Linux >= 4.19.37 < 4.20
• Linux >= 5.0.10 < 5.1
• Linux 5.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.