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usb: cdc-acm: Fix handling of oversized fragments

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commit 12e712964f41d05ae034989892de445781c46730 upstream.

If we receive an initial fragment of size 8 bytes which specifies a wLength
of 1 byte (so the reassembled message is supposed to be 9 bytes long), and
we then receive a second fragment of size 9 bytes (which is not supposed to
happen), we currently wrongly bypass the fragment reassembly code but still
pass the pointer to the acm->notification_buffer to
acm_process_notification().

Make this less wrong by always going through fragment reassembly when we
expect more fragments.

Before this patch, receiving an overlong fragment could lead to `newctrl`
in acm_process_notification() being uninitialized data (instead of data
coming from the device).

Cc: stable <stable@kernel.org>
Fixes: ea2583529c ("cdc-acm: reassemble fragmented notifications")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jann Horn 2025-02-12 19:15:16 +01:00 • committed by Greg Kroah-Hartman
commit 7cfb70e97f
1 changed files with 1 additions and 1 deletions
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2
drivers/usb/class/cdc-acm.c
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@ -404,7 +404,7 @@ static void acm_ctrl_irq(struct urb *urb)
expected_size = sizeof(struct usb_cdc_notification) +
le16_to_cpu(dr->wLength);
if (current_size < expected_size) {
if (acm->nb_index != 0 || current_size < expected_size) {
/* notification is transmitted fragmented, reassemble */
if (acm->nb_size < expected_size) {
u8 *new_buffer;