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Fri, 05 Sep 2025 18:20:18 -0700 (PDT) Received: from localhost ([149.102.246.10]) by smtp.gmail.com with UTF8SMTPSA id 4fb4d7f45d1cf-61cfc4e50fbsm17060426a12.38.2025.09.05.18.20.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Sep 2025 18:20:18 -0700 (PDT) From: Stanislav Fort X-Google-Original-From: Stanislav Fort To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, linux-hams@vger.kernel.org, linux-kernel@vger.kernel.org, security@kernel.org, Stanislav Fort , stable@vger.kernel.org Subject: [PATCH net v4] netrom: linearize and validate lengths in nr_rx_frame() Date: Sat, 6 Sep 2025 04:20:16 +0300 Message-Id: <20250906012016.58856-1-disclosure@aisle.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 (>=3D 21 bytes). - For CONNREQ handling, ensure window (byte 20) and user address (bytes 21-27) are present (>=3D 28 bytes). - Preserve existing BPQ extension handling: - NR_CONNACK len =3D=3D 22 -> 1 extra byte (TTL) - NR_CONNREQ len =3D=3D 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 Reviewed-by: Eric Dumazet Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Stanislav Fort --- 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 =3D (ax25_address *)(skb->data + 0); dest =3D (ax25_address *)(skb->data + 7); @@ -927,6 +932,11 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device= *dev) } if (sk !=3D NULL) { + if (frametype =3D=3D 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_devic= e *dev) return 0; } - sk =3D 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 =3D (ax25_address *)(skb->data + 21); + sk =3D nr_find_listener(dest); + if (sk =3D=3D NULL || sk_acceptq_is_full(sk) || (make =3D nr_make_new(sk)) =3D=3D NULL) { nr_transmit_refusal(skb, 0); --=20 2.39.3 (Apple Git-146)