linux-hardening - [PATCH] USB: serial: Fix heap overflow in WHITEHEAT_GET_DTR

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Date:   Mon, 18 Apr 2022 21:17:42 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        kernel test robot <lkp@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] USB: serial: Fix heap overflow in WHITEHEAT_GET_DTR_RTS

This looks like it's harmless, as both the source and the destinations are
currently the same allocation size (4 bytes) and don't use their padding,
but if anything were to ever be added after the "mcr" member in "struct
whiteheat_private", it would be overwritten. The structs both have a
single u8 "mcr" member, but are 4 bytes in padded size. The memcpy()
destination was explicitly targeting the u8 member (size 1) with the
length of the whole structure (size 4), triggering the memcpy buffer
overflow warning:

In file included from include/linux/string.h:253,
                 from include/linux/bitmap.h:11,
                 from include/linux/cpumask.h:12,
                 from include/linux/smp.h:13,
                 from include/linux/lockdep.h:14,
                 from include/linux/spinlock.h:62,
                 from include/linux/mmzone.h:8,
                 from include/linux/gfp.h:6,
                 from include/linux/slab.h:15,
                 from drivers/usb/serial/whiteheat.c:17:
In function 'fortify_memcpy_chk',
    inlined from 'firm_send_command' at drivers/usb/serial/whiteheat.c:587:4:
include/linux/fortify-string.h:328:25: warning: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
  328 |                         __write_overflow_field(p_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Expand the memcpy() to the entire structure, though perhaps the correct
solution is to mark all the USB command structures as "__packed".

Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/202204142318.vDqjjSFn-lkp@intel.com
Cc: Johan Hovold <johan@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/usb/serial/whiteheat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/serial/whiteheat.c b/drivers/usb/serial/whiteheat.c
index da65d14c9ed5..6e00498843fb 100644
--- a/drivers/usb/serial/whiteheat.c
+++ b/drivers/usb/serial/whiteheat.c
@@ -584,7 +584,7 @@ static int firm_send_command(struct usb_serial_port *port, __u8 command,
 		switch (command) {
 		case WHITEHEAT_GET_DTR_RTS:
 			info = usb_get_serial_port_data(port);
-			memcpy(&info->mcr, command_info->result_buffer,
+			memcpy(info, command_info->result_buffer,
 					sizeof(struct whiteheat_dr_info));
 				break;
 		}
-- 
2.32.0