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[68.48.65.54]) by smtp.gmail.com with ESMTPSA id af79cd13be357-92ee5baaab7sm1500521585a.19.2026.07.14.04.49.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2026 04:49:07 -0700 (PDT) From: Michael Bommarito To: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Antoine Tenart , Simon Horman , Tom Herbert , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH net v2] ila: reload IPv6 header after pskb_may_pull in checksum adjust Date: Tue, 14 Jul 2026 07:49:03 -0400 Message-ID: <20260714114903.3763420-1-michael.bommarito@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7bit ila_csum_adjust_transport() caches ip6h = ipv6_hdr(skb) before calling pskb_may_pull(). On a non-linear skb whose transport header sits in a page fragment, pskb_may_pull() can call __pskb_pull_tail() / pskb_expand_head() and free the old skb head, leaving ip6h dangling; the following get_csum_diff(ip6h, p) then reads freed memory. ila_update_ipv6_locator() uses ip6h (and the iaddr derived from it) again after the csum-adjust call and additionally writes the new locator through that pointer. Impact: a remote IPv6 packet routed through a configured ILA csum-adjust-transport route or receive-side mapping triggers a slab-use-after-free in ila_update_ipv6_locator() (KASAN). The route or mapping requires CAP_NET_ADMIN to configure, but trigger packets are unauthenticated once it exists. Reload ip6h after each pskb_may_pull() in ila_csum_adjust_transport() before the csum-diff read. In ila_update_ipv6_locator() only the ILA_CSUM_ADJUST_TRANSPORT case pulls the skb, so reload ip6h and iaddr in that case alone before the destination-address write; the neutral-map modes never pull and keep their cached pointers. Fixes: 33f11d16142b ("ila: Create net/ipv6/ila directory") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito --- v2: In ila_update_ipv6_locator() reload ip6h/iaddr only in the ILA_CSUM_ADJUST_TRANSPORT case instead of unconditionally, per Antoine Tenart's review; the neutral-map modes never pull the skb, so their cached pointers remain valid. v1: https://lore.kernel.org/netdev/20260711150648.2915106-1-michael.bommarito@gmail.com/ Evidence: a KUnit case on UML+KASAN drives ila_update_ipv6_locator() with a non-linear skb whose transport header sits in a fragment, so the pskb_may_pull() in ila_csum_adjust_transport() reallocates the head. Stock: BUG: KASAN: slab-use-after-free in ila_update_ipv6_locator, Read of size 4 (the stale ip6h/iaddr). Patched: both the valid-linear control and the fragmented case pass, KASAN-clean. Built clean, no new warnings. net/ipv6/ila/ila_common.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/net/ipv6/ila/ila_common.c b/net/ipv6/ila/ila_common.c index e71571455c8a0..b78179bfc4c72 100644 --- a/net/ipv6/ila/ila_common.c +++ b/net/ipv6/ila/ila_common.c @@ -85,6 +85,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, struct tcphdr *th = (struct tcphdr *) (skb_network_header(skb) + nhoff); + ip6h = ipv6_hdr(skb); diff = get_csum_diff(ip6h, p); inet_proto_csum_replace_by_diff(&th->check, skb, diff, true, true); @@ -96,6 +97,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, (skb_network_header(skb) + nhoff); if (uh->check || skb->ip_summed == CHECKSUM_PARTIAL) { + ip6h = ipv6_hdr(skb); diff = get_csum_diff(ip6h, p); inet_proto_csum_replace_by_diff(&uh->check, skb, diff, true, true); @@ -110,6 +112,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, struct icmp6hdr *ih = (struct icmp6hdr *) (skb_network_header(skb) + nhoff); + ip6h = ipv6_hdr(skb); diff = get_csum_diff(ip6h, p); inet_proto_csum_replace_by_diff(&ih->icmp6_cksum, skb, diff, true, true); @@ -127,6 +130,15 @@ void ila_update_ipv6_locator(struct sk_buff *skb, struct ila_params *p, switch (p->csum_mode) { case ILA_CSUM_ADJUST_TRANSPORT: ila_csum_adjust_transport(skb, p); + /* + * ila_csum_adjust_transport() calls pskb_may_pull(), which can + * reallocate the skb head and leave ip6h (and the iaddr derived + * from it) dangling; reload both before the write below. The + * other csum modes do not pull, so their cached pointers stay + * valid. + */ + ip6h = ipv6_hdr(skb); + iaddr = ila_a2i(&ip6h->daddr); break; case ILA_CSUM_NEUTRAL_MAP: if (sir2ila) { -- 2.53.0