ipvs: reload ip header after head reallocation

[PATCH 5.10/6.1] ipvs: reload ip header after head reallocation

Posted by Denis Arefev 4 weeks, 1 day ago

From: Florian Westphal <fw@strlen.de>

commit a2f57827bf7c695b8c72dc4511cae8e86582369d upstream.

__ip_vs_get_out_rt() calls skb_ensure_writable() which may
reallocate skb->head.

Fixes: 8d8e20e2d7bb ("ipvs: Decrement ttl")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-sonnet-4-6
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Florian Westphal <fw@strlen.de>
[Denis Arefev: adapted for 5.10/6.1: keep EnterFunction/LeaveFunction
instrumentation]
Signed-off-by: Denis Arefev <arefev@swemel.ru>
---
Backport fix for CVE-2026-68476 
Link: https://nvd.nist.gov/vuln/detail/CVE-2026-68476 
---
 net/netfilter/ipvs/ip_vs_xmit.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_xmit.c b/net/netfilter/ipvs/ip_vs_xmit.c
index 9e199f00eea7..29ca141e3795 100644
--- a/net/netfilter/ipvs/ip_vs_xmit.c
+++ b/net/netfilter/ipvs/ip_vs_xmit.c
@@ -718,15 +718,13 @@ int
 ip_vs_bypass_xmit(struct sk_buff *skb, struct ip_vs_conn *cp,
 		  struct ip_vs_protocol *pp, struct ip_vs_iphdr *ipvsh)
 {
-	struct iphdr  *iph = ip_hdr(skb);
-
 	EnterFunction(10);
 
-	if (__ip_vs_get_out_rt(cp->ipvs, cp->af, skb, NULL, iph->daddr,
-			       IP_VS_RT_MODE_NON_LOCAL, NULL, ipvsh) < 0)
+	if (__ip_vs_get_out_rt(cp->ipvs, cp->af, skb, NULL, ip_hdr(skb)->daddr,
+			       IP_VS_RT_MODE_NON_LOCAL, NULL, ipvsh) < 0)
 		goto tx_error;
 
-	ip_send_check(iph);
+	ip_send_check(ip_hdr(skb));
 
 	/* Another hack: avoid icmp_send in ip_fragment */
 	skb->ignore_df = 1;
-- 
2.43.0

Re: [PATCH 5.10/6.1] ipvs: reload ip header after head reallocation

Posted by Sasha Levin 4 weeks ago

> commit a2f57827bf7c695b8c72dc4511cae8e86582369d upstream.
>
> __ip_vs_get_out_rt() calls skb_ensure_writable() which may
> reallocate skb->head.

Queued for 6.1, 5.15 and 5.10, thanks.  5.15 has the same dangling iph in
ip_vs_bypass_xmit(), so I applied the same patch there as well.

-- 
Thanks,
Sasha

Re: [PATCH 5.10/6.1] ipvs: reload ip header after head reallocation

Posted by Breno Leitao 4 weeks, 1 day ago

On Fri, Aug 28, 2026 at 11:55:21AM +0300, Denis Arefev wrote:
> From: Florian Westphal <fw@strlen.de>
> 
> commit a2f57827bf7c695b8c72dc4511cae8e86582369d upstream.
> 
> __ip_vs_get_out_rt() calls skb_ensure_writable() which may
> reallocate skb->head.
> 
> Fixes: 8d8e20e2d7bb ("ipvs: Decrement ttl")
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-sonnet-4-6
> Acked-by: Julian Anastasov <ja@ssi.bg>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> [Denis Arefev: adapted for 5.10/6.1: keep EnterFunction/LeaveFunction
> instrumentation]

yea, the backport seems fine and match commit a2f57827bf7c69 ("ipvs:
reload ip header after head reallocation")

> Signed-off-by: Denis Arefev <arefev@swemel.ru>

Reviewed-by: Breno Leitao <leitao@debian.org>