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Message-ID: <20240924150257.1059524-3-edumazet@google.com>
Date: Tue, 24 Sep 2024 15:02:57 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
Willem de Bruijn <willemb@...gle.com>, Jonathan Davies <jonathan.davies@...anix.com>, eric.dumazet@...il.com,
Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 2/2] net: add more sanity checks to qdisc_pkt_len_init()
One path takes care of SKB_GSO_DODGY, assuming
skb->len is bigger than hdr_len.
virtio_net_hdr_to_skb() does not fully dissect TCP headers,
it only make sure it is at least 20 bytes.
It is possible for an user to provide a malicious 'GSO' packet,
total length of 80 bytes.
- 20 bytes of IPv4 header
- 60 bytes TCP header
- a small gso_size like 8
virtio_net_hdr_to_skb() would declare this packet as a normal
GSO packet, because it would see 40 bytes of payload,
bigger than gso_size.
We need to make detect this case to not underflow
qdisc_skb_cb(skb)->pkt_len.
Fixes: 1def9238d4aa ("net_sched: more precise pkt_len computation")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
net/core/dev.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index f2c47da79f17d5ebe6b334b63d66c84c84c519fc..35b8bcfb209bd274c81380eaf6e445641306b018 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3766,10 +3766,14 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
hdr_len += sizeof(struct udphdr);
}
- if (shinfo->gso_type & SKB_GSO_DODGY)
- gso_segs = DIV_ROUND_UP(skb->len - hdr_len,
- shinfo->gso_size);
+ if (unlikely(shinfo->gso_type & SKB_GSO_DODGY)) {
+ int payload = skb->len - hdr_len;
+ /* Malicious packet. */
+ if (payload <= 0)
+ return;
+ gso_segs = DIV_ROUND_UP(payload, shinfo->gso_size);
+ }
qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len;
}
}
--
2.46.0.792.g87dc391469-goog
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