6.12-stable review patch. If anyone has any objections, please let me know.
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From: Slavin Liu slavin452@gmail.com
[ Upstream commit ad891bb3d079a46a821bf2b8867854645191bab0 ]
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
Fixes: ed0de45a1008 ("ipv4: recompile ip options in ipv4_link_failure") Signed-off-by: Slavin Liu slavin452@gmail.com Acked-by: Julian Anastasov ja@ssi.bg Signed-off-by: Florian Westphal fw@strlen.de Signed-off-by: Sasha Levin sashal@kernel.org --- net/netfilter/ipvs/ip_vs_xmit.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/netfilter/ipvs/ip_vs_xmit.c b/net/netfilter/ipvs/ip_vs_xmit.c index 014f077403695..fa2db17f6298b 100644 --- a/net/netfilter/ipvs/ip_vs_xmit.c +++ b/net/netfilter/ipvs/ip_vs_xmit.c @@ -409,6 +409,9 @@ __ip_vs_get_out_rt(struct netns_ipvs *ipvs, int skb_af, struct sk_buff *skb, return -1;
err_unreach: + if (!skb->dev) + skb->dev = skb_dst(skb)->dev; + dst_link_failure(skb); return -1; }