Linearize skb and add targeted length checks in nr_rx_frame() to prevent out-of-bounds reads and potential use-after-free (UAF) when processing malformed NET/ROM frames.

- Require skb to be linear and 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). - Preserve existing BPQ extension handling: - NR_CONNACK len == 22 -> 1 extra byte (TTL) - NR_CONNREQ len == 37 -> 2 extra bytes (timeout)

These validations block malformed frames from triggering bounds violations via short skbs. Because NET/ROM frames may originate from remote peers, the issue is externally triggerable and therefore security-relevant.

Suggested-by: Eric Dumazet edumazet@google.com Reviewed-by: Eric Dumazet edumazet@google.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Stanislav Fort disclosure@aisle.com --- Changes since v3: - Wrap commit message at 74 columns - Add Fixes tag and Cc: stable - Drop Reported-by - Add Reviewed-by from Eric Dumazet --- 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);