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[68.48.65.54]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8e7d64cc559sm228562585a.13.2026.04.17.17.01.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Apr 2026 17:01:44 -0700 (PDT) From: Michael Bommarito To: Marcel Holtmann , Luiz Augusto von Dentz , linux-bluetooth@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Soenke Huster , "Michael S . Tsirkin" , virtualization@lists.linux.dev Subject: [PATCH] Bluetooth: virtio_bt: clamp rx length before skb_put Date: Fri, 17 Apr 2026 20:01:38 -0400 Message-ID: <20260418000138.1848813-1-michael.bommarito@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit virtbt_rx_work() calls skb_put(skb, len) where len comes directly from virtqueue_get_buf() with no validation against the skb we posted. The RX skb is allocated as alloc_skb(1000) in virtbt_add_inbuf(). A malicious or buggy virtio-bt backend that reports used.len larger than the skb's tailroom causes skb_put() to call skb_over_panic() in net/core/skbuff.c, which triggers BUG() and panics the guest. Reproduced on a QEMU 9.0 whose virtio-bt backend reports used.len = 4096 into a 1000-byte rx skb: skbuff: skb_over_panic: text:ffffffff83958e84 len:4096 put:4096 head:ffff88800c071000 data:ffff88800c071000 tail:0x1000 end:0x6c0 dev: ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:214! Call Trace: skb_panic+0x160/0x162 skb_put.cold+0x31/0x31 virtbt_rx_work+0x94/0x250 process_one_work+0x80d/0x1510 worker_thread+0x4af/0xd20 kthread+0x2cc/0x3a0 Reject any len that exceeds skb_tailroom(). Drop the skb on the error path; virtbt_add_inbuf() reposts a fresh one for the next iteration. With the check in place the same harness runs without BUG(); the driver logs "rx reply len %u exceeds skb tailroom %u" and the device keeps running. Same class of bug as commit c04db81cd028 ("net/9p: Fix buffer overflow in USB transport layer"), which hardened the USB 9p transport against unchecked device-reported length. Fixes: 160fbcf3bfb9 ("Bluetooth: virtio_bt: Use skb_put to set length") Cc: stable@vger.kernel.org Cc: Soenke Huster Signed-off-by: Michael Bommarito Assisted-by: Claude:claude-opus-4-7 --- drivers/bluetooth/virtio_bt.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/bluetooth/virtio_bt.c b/drivers/bluetooth/virtio_bt.c index 76d61af8a275..157e68b6e75f 100644 --- a/drivers/bluetooth/virtio_bt.c +++ b/drivers/bluetooth/virtio_bt.c @@ -227,8 +227,15 @@ static void virtbt_rx_work(struct work_struct *work) if (!skb) return; - skb_put(skb, len); - virtbt_rx_handle(vbt, skb); + if (len > skb_tailroom(skb)) { + bt_dev_err(vbt->hdev, + "rx reply len %u exceeds skb tailroom %u\n", + len, skb_tailroom(skb)); + kfree_skb(skb); + } else { + skb_put(skb, len); + virtbt_rx_handle(vbt, skb); + } if (virtbt_add_inbuf(vbt) < 0) return; -- 2.53.0