On Wed, Oct 18, 2023 at 04:07:32PM -0700, Kees Cook wrote: > The memcpy() in bch2_bkey_append_ptr() is operating on an embedded fake > flexible array which looks to the compiler like it has 0 size. This > causes W=1 builds to emit warnings due to -Wstringop-overflow: > > In file included from include/linux/string.h:254, > 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/radix-tree.h:14, > from include/linux/backing-dev-defs.h:6, > from fs/bcachefs/bcachefs.h:182: > fs/bcachefs/extents.c: In function 'bch2_bkey_append_ptr': > include/linux/fortify-string.h:57:33: warning: writing 8 bytes into a > region of size 0 [-Wstringop-overflow=] > 57 | #define __underlying_memcpy __builtin_memcpy > | ^ > include/linux/fortify-string.h:648:9: note: in expansion of macro > '__underlying_memcpy' > 648 | __underlying_##op(p, q, __fortify_size); > \ > | ^~~~~~~~~~~~~ > include/linux/fortify-string.h:693:26: note: in expansion of macro > '__fortify_memcpy_chk' > 693 | #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, > \ > | ^~~~~~~~~~~~~~~~~~~~ > fs/bcachefs/extents.c:235:17: note: in expansion of macro 'memcpy' > 235 | memcpy((void *) &k->v + bkey_val_bytes(&k->k), > | ^~~~~~ > fs/bcachefs/bcachefs_format.h:287:33: note: destination object 'v' of size > 0 > 287 | struct bch_val v; > | ^ > > Avoid making any structure changes and just replace the u64 copy into a > direct assignment, side-stepping the entire problem.
This does make me wonder about the usefulness of the fortify source stuff if it can be sidestepped this way, but hey, I'll take it :) Pulled it into the testing branch, https://evilpiepirate.org/~testdashboard/ci?branch=bcachefs-testing
