The sizeof(struct whitehat_dr_info) can be 4 bytes under CONFIG_AEABI=n due to "-mabi=apcs-gnu", even though it has a single u8:

whiteheat_private { __u8 mcr; /* 0 1 */

/* size: 4, cachelines: 1, members: 1 */ /* padding: 3 */ /* last cacheline: 4 bytes */ };

The result is technically 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); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Instead, just assign the one byte directly.

Reported-by: kernel test robot lkp@intel.com Link: https://lore.kernel.org/lkml/202204142318.vDqjjSFn-lkp@intel.com Cc: Johan Hovold johan@kernel.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: linux-usb@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Kees Cook keescook@chromium.org --- v1: https://lore.kernel.org/lkml/20220419041742.4117026-1-keescook@chromium.org/ v2: - just assign the single byte --- drivers/usb/serial/whiteheat.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/whiteheat.c b/drivers/usb/serial/whiteheat.c index da65d14c9ed5..06aad0d727dd 100644 --- a/drivers/usb/serial/whiteheat.c +++ b/drivers/usb/serial/whiteheat.c @@ -584,9 +584,8 @@ 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, - sizeof(struct whiteheat_dr_info)); - break; + info->mcr = command_info->result_buffer[0]; + break; } } exit: