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ila: reload IPv6 header after pskb_may_pull in checksum adjust

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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: 33f11d1614 ("ila: Create net/ipv6/ila directory")
Cc: stable@vger.kernel.org
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://patch.msgid.link/20260714114903.3763420-1-michael.bommarito@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Michael Bommarito 2026-07-14 07:49:03 -04:00 committed by Jakub Kicinski
parent 34a71f5361
commit 92d3817649
1 changed files with 12 additions and 0 deletions
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12
net/ipv6/ila/ila_common.c
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@ -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) {