From 9a86bee66ecd37e6b56ba9f35db29d7e33cc5317 Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@google.com>
Date: Wed, 12 Feb 2025 19:15:16 +0100
Subject: [PATCH] usb: cdc-acm: Fix handling of oversized fragments
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: ea2583529cd1 ("cdc-acm: reassemble fragmented notifications")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/class/cdc-acm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 27d0a8cb0fe52..ead891de5e1dc 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -405,7 +405,7 @@ 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;
--
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