[PATCH net] esp: fix out-of-bounds transport-header read after exthdr walk

[Henry Martin <bsdhenrymartin@gmail.com>]

esp6_input_done2() computes the transport header offset with
ipv6_skip_exthdr(), which walks the extension header chain using the
packet's self-reported header lengths without ever comparing the
running offset against skb->len, so it can return an offset past the
end of the packet.  esp6_input_done2() then reads the 2-byte source
port at skb->data + offset out of bounds.

esp4's esp_input_done2() has the same class of problem from a
different direction: ihl is taken from the decrypted inner packet and
is not re-validated after esp_remove_trailer() shrank the skb, so the
2-byte source port read at skb_network_header + ihl can land past the
new end of the packet.

Reject the packet with -EINVAL when there is no room for the port at
the computed offset.

This issue was discovered by Tencent CodeBuddy Security.

Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
---
 net/ipv4/esp4.c | 12 ++++++++++++
 net/ipv6/esp6.c | 11 +++++++++++
 2 files changed, 23 insertions(+)

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index e76db5817e78e..aaff5a2b659db 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -744,6 +744,18 @@ int esp_input_done2(struct sk_buff *skb, int err)
 		struct udphdr *uh = (void *)(skb_network_header(skb) + ihl);
 		__be16 source;

+		/*
+		 * ihl is taken from the decrypted inner packet and is not
+		 * re-validated after esp_remove_trailer() shrank the skb;
+		 * make sure the 2-byte source port we read below is within
+		 * the packet.
+		 */
+		if (skb_network_offset(skb) + ihl + sizeof(__be16) >
+		    skb->len) {
+			err = -EINVAL;
+			goto out;
+		}
+
 		switch (x->encap->encap_type) {
 		case TCP_ENCAP_ESPINTCP:
 			source = th->source;
diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index b1c9b36f76dc4..89e8cdf5a26b2 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -782,6 +782,17 @@ int esp6_input_done2(struct sk_buff *skb, int err)
 			goto out;
 		}

+		/*
+		 * ipv6_skip_exthdr() can advance past the packet end when the
+		 * last extension header claims an oversized length; the
+		 * transport header below would then be read out of bounds.
+		 * Make sure there is room for the 2-byte source port we read.
+		 */
+		if (offset + sizeof(__be16) > skb->len) {
+			err = -EINVAL;
+			goto out;
+		}
+
 		uh = (void *)(skb->data + offset);
 		th = (void *)(skb->data + offset);
 		hdr_len += offset;
--
2.43.7