6.12-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
commit e563b01208f4d1f609bcab13333b6c0e24ce6a01 upstream.
If the first fragment is shorter than struct usb_cdc_notification, we can't calculate an expected_size. Log an error and discard the notification instead of reading lengths from memory outside the received data, which can lead to memory corruption when the expected_size decreases between fragments, causing `expected_size - acm->nb_index` to wrap.
This issue has been present since the beginning of git history; however, it only leads to memory corruption since commit ea2583529cd1 ("cdc-acm: reassemble fragmented notifications").
A mitigating factor is that acm_ctrl_irq() can only execute after userspace has opened /dev/ttyACM*; but if ModemManager is running, ModemManager will do that automatically depending on the USB device's vendor/product IDs and its other interfaces.
Cc: stable stable@kernel.org Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/class/cdc-acm.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
--- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -371,7 +371,7 @@ static void acm_process_notification(str static void acm_ctrl_irq(struct urb *urb) { struct acm *acm = urb->context; - struct usb_cdc_notification *dr = urb->transfer_buffer; + struct usb_cdc_notification *dr; unsigned int current_size = urb->actual_length; unsigned int expected_size, copy_size, alloc_size; int retval; @@ -398,9 +398,20 @@ static void acm_ctrl_irq(struct urb *urb
usb_mark_last_busy(acm->dev);
- if (acm->nb_index) + if (acm->nb_index == 0) { + /* + * The first chunk of a message must contain at least the + * notification header with the length field, otherwise we + * can't get an expected_size. + */ + if (current_size < sizeof(struct usb_cdc_notification)) { + dev_dbg(&acm->control->dev, "urb too short\n"); + goto exit; + } + dr = urb->transfer_buffer; + } else { dr = (struct usb_cdc_notification *)acm->notification_buffer; - + } /* size = notification-header + (optional) data */ expected_size = sizeof(struct usb_cdc_notification) + le16_to_cpu(dr->wLength);