Messages in this thread Patch in this message | | | From | Alexander Shishkin <> | Subject | [PATCH v1 4/6] virtio console: Harden control message handling | Date | Thu, 19 Jan 2023 15:57:19 +0200 |
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In handle_control_message(), we look at the ->event field twice, which gives a malicious VMM a window in which to switch it from PORT_ADD to PORT_REMOVE, triggering a null dereference further down the line:
RIP: 0010:spin_lock_irq ./include/linux/spinlock.h:388 RIP: 0010:unplug_port+0x9/0x150 drivers/char/virtio_console.c:1512 Call Trace: handle_control_message+0x108/0x2c0 drivers/char/virtio_console.c:1600 elfcorehdr_read+0x40/0x40 ??:? process_one_work+0x1b4/0x310 kernel/workqueue.c:2297 worker_thread+0x5c/0x3a0 kernel/workqueue.c:2444 kthread+0x120/0x140 kernel/kthread.c:319 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Read the event code once instead, basing all following decisions on the same value.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Amit Shah <amit@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- drivers/char/virtio_console.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c index 6599c2956ba4..62f69f949cb7 100644 --- a/drivers/char/virtio_console.c +++ b/drivers/char/virtio_console.c @@ -1563,22 +1563,22 @@ static void handle_control_message(struct virtio_device *vdev, struct port *port; size_t name_size; int err; - unsigned id; + unsigned id, event; cpkt = (struct virtio_console_control *)(buf->buf + buf->offset); - /* Make sure the host cannot change id under us */ + /* Make sure the host cannot change id or event under us */ id = virtio32_to_cpu(vdev, READ_ONCE(cpkt->id)); + event = virtio16_to_cpu(vdev, cpkt->event); port = find_port_by_id(portdev, id); - if (!port && - cpkt->event != cpu_to_virtio16(vdev, VIRTIO_CONSOLE_PORT_ADD)) { + if (!port && event != VIRTIO_CONSOLE_PORT_ADD) { /* No valid header at start of buffer. Drop it. */ dev_dbg(&portdev->vdev->dev, "Invalid index %u in control packet\n", cpkt->id); return; } - switch (virtio16_to_cpu(vdev, cpkt->event)) { + switch (event) { case VIRTIO_CONSOLE_PORT_ADD: if (port) { dev_dbg(&portdev->vdev->dev, -- 2.39.0
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