[PATCH net v3 1/2] geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint

[Xiang Mei <xmei5@asu.edu>]

geneve_gro_receive() reads the GRO hint through geneve_sk_gro_hint_off(),
which honours it only when the socket enabled IFLA_GENEVE_GRO_HINT
(gs->gro_hint). geneve_gro_complete() instead calls the low-level
geneve_opt_gro_hint_off() and acts on the hint unconditionally.

On a tunnel without the hint, receive aggregates the frames as plain
ETH_P_TEB while complete still honours an attacker-supplied hint option: it
inflates gh_len by gro_hint->nested_hdr_len (u8) and redirects the dispatch
type, so the inner gro_complete handler runs at nhoff + gh_len, an offset
receive never pulled nor validated, reading out of bounds of the skb head:

  BUG: KASAN: slab-out-of-bounds in ipv6_gro_complete (net/ipv6/ip6_offload.c:196)
  Read of size 1 at addr ffff88800fe91980 by task exploit/153
   ipv6_gro_complete (net/ipv6/ip6_offload.c:196)
   geneve_gro_complete (drivers/net/geneve.c:965)
   udp_gro_complete (net/ipv4/udp_offload.c:940)
   inet_gro_complete (net/ipv4/af_inet.c:1621)
   __gro_flush (net/core/gro.c:306)

Gate the complete path on gs->gro_hint too via geneve_sk_gro_hint_off(), so
both paths agree. Tunnels that enable the hint are unaffected.

Fixes: fd0dd796576e ("geneve: use GRO hint option in the RX path")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Reported-by: Kyle Zeng <kylebot@openai.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@asu.edu>
---
 drivers/net/geneve.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 9afff7bcaa0b..7cf7aaac8ee1 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -954,13 +954,13 @@ static int geneve_gro_complete(struct sock *sk, struct sk_buff *skb,
 	struct genevehdr *gh;
 	struct packet_offload *ptype;
 	__be16 type;
-	int gh_len;
+	unsigned int gh_len;
 	int err = -ENOSYS;
 
 	gh = (struct genevehdr *)(skb->data + nhoff);
 	gh_len = geneve_hlen(gh);
 	type = gh->proto_type;
-	geneve_opt_gro_hint_off(gh, &type, &gh_len);
+	geneve_sk_gro_hint_off(sk, gh, &type, &gh_len);
 
 	/* since skb->encapsulation is set, eth_gro_complete() sets the inner mac header */
 	if (likely(type == htons(ETH_P_TEB)))
-- 
2.43.0