On Wed, Apr 20, 2022 at 10:14 AM Johan Hovold <johan@xxxxxxxxxx> wrote: > On Mon, Apr 18, 2022 at 09:17:42PM -0700, Kees Cook wrote: > > 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: > > Ehh... No. The size of a structure with a single u8 is 1, not 4. There's > nothing wrong with the current code even if the use of memcpy for this > is a bit odd. > > > 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); > > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > So something is confused here. So something's going wrong in fortify_memcpy_chk()? It looks like it is called with constant "size" equal to 1, and the condition "p_size_field < size" (with an unsigned comparison) is either true (meaning p_size_field would have to be 0) or not known at compile time? The original report says it happened when compiling with CONFIG_CC_OPTIMIZE_FOR_SIZE=y, maybe that matters?
