On Tue, Oct 10, 2023 at 04:56:12PM -0700, Kees Cook wrote: > The memcpy() in bch2_bkey_append_ptr() is operating on an embedded > fake flexible array. Instead, make it explicit, and convert the memcpy > to target the flexible array instead. Fixes the W=1 warning seen for > -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; > | ^ > > Cc: Kent Overstreet <[email protected]> > Cc: Brian Foster <[email protected]> > Cc: [email protected] > Reported-by: kernel test robot <[email protected]> > Closes: > https://lore.kernel.org/oe-kbuild-all/[email protected]/ > Signed-off-by: Kees Cook <[email protected]> > --- > fs/bcachefs/bcachefs_format.h | 5 ++++- > fs/bcachefs/extents.h | 2 +- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/fs/bcachefs/bcachefs_format.h b/fs/bcachefs/bcachefs_format.h > index f0d130440baa..f5e8cb43697b 100644 > --- a/fs/bcachefs/bcachefs_format.h > +++ b/fs/bcachefs/bcachefs_format.h > @@ -300,7 +300,10 @@ struct bkey_i { > __u64 _data[0]; > > struct bkey k; > - struct bch_val v; > + union { > + struct bch_val v; > + DECLARE_FLEX_ARRAY(__u8, bytes); > + }; > };
Hi Kees, I'm curious if this is something that could be buried in bch_val given it's already kind of a fake structure..? If not, my only nitty comment is that memcpy(k->bytes[], ...) makes it kind of read like we're copying in opaque key data rather than value data, so perhaps a slightly more descriptive field name would be helpful. But regardless I'd wait until Kent has a chance to comment before changing anything.. Brian > > #define KEY(_inode, _offset, _size) \ > diff --git a/fs/bcachefs/extents.h b/fs/bcachefs/extents.h > index 7ee8d031bb6c..6248e17bbac5 100644 > --- a/fs/bcachefs/extents.h > +++ b/fs/bcachefs/extents.h > @@ -642,7 +642,7 @@ static inline void bch2_bkey_append_ptr(struct bkey_i *k, > struct bch_extent_ptr > > ptr.type = 1 << BCH_EXTENT_ENTRY_ptr; > > - memcpy((void *) &k->v + bkey_val_bytes(&k->k), > + memcpy(&k->bytes[bkey_val_bytes(&k->k)], > &ptr, > sizeof(ptr)); > k->k.u64s++; > -- > 2.34.1 >
