On Wed, Oct 18, 2023 at 08:32:32PM -0400, Kent Overstreet wrote: > 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 :)
Well, the "weird" cases like this are the ones that get attention. All the places it's working more cleanly are very effectively stomping real bugs. > Pulled it into the testing branch, > https://evilpiepirate.org/~testdashboard/ci?branch=bcachefs-testing Thanks! -Kees -- Kees Cook
