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Message-Id: <20250903181915.6359-1-disclosure@aisle.com>
Date: Wed, 3 Sep 2025 21:19:15 +0300
From: Stanislav Fort <stanislav.fort@...le.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
edumazet@...gle.com,
kuba@...nel.org,
pabeni@...hat.com,
horms@...nel.org,
linux-hams@...r.kernel.org,
linux-kernel@...r.kernel.org,
security@...nel.org,
Stanislav Fort <disclosure@...le.com>
Subject: [PATCH net v3] netrom: linearize and validate lengths in nr_rx_frame()
Linearize skb and add targeted length checks in nr_rx_frame() to avoid out-of-bounds reads and potential use-after-free when processing malformed NET/ROM frames.
- Linearize skb and require at least NR_NETWORK_LEN + NR_TRANSPORT_LEN (20 bytes) before reading network/transport fields.
- For existing sockets path, ensure NR_CONNACK includes the window byte (>= 21 bytes).
- For CONNREQ handling, ensure window (byte 20) and user address (bytes 21-27) are present (>= 28 bytes).
- Maintain existing BPQ extension handling:
- NR_CONNACK len == 22 implies 1 extra byte (TTL)
- NR_CONNREQ len == 37 implies 2 extra bytes (timeout)
Suggested-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Stanislav Fort <disclosure@...le.com>
Signed-off-by: Stanislav Fort <disclosure@...le.com>
---
net/netrom/af_netrom.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
index 3331669d8e33..f0660dd6d3b0 100644
--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -885,6 +885,11 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
* skb->data points to the netrom frame start
*/
+ if (skb_linearize(skb))
+ return 0;
+ if (skb->len < NR_NETWORK_LEN + NR_TRANSPORT_LEN)
+ return 0;
+
src = (ax25_address *)(skb->data + 0);
dest = (ax25_address *)(skb->data + 7);
@@ -927,6 +932,11 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
}
if (sk != NULL) {
+ if (frametype == NR_CONNACK &&
+ skb->len < NR_NETWORK_LEN + NR_TRANSPORT_LEN + 1) {
+ sock_put(sk);
+ return 0;
+ }
bh_lock_sock(sk);
skb_reset_transport_header(skb);
@@ -961,10 +971,14 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
return 0;
}
- sk = nr_find_listener(dest);
+ /* Need window (byte 20) and user address (bytes 21-27) */
+ if (skb->len < NR_NETWORK_LEN + NR_TRANSPORT_LEN + 1 + AX25_ADDR_LEN)
+ return 0;
user = (ax25_address *)(skb->data + 21);
+ sk = nr_find_listener(dest);
+
if (sk == NULL || sk_acceptq_is_full(sk) ||
(make = nr_make_new(sk)) == NULL) {
nr_transmit_refusal(skb, 0);
--
2.39.3 (Apple Git-146)
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