From 7413ab70cbc15bd8f35a78569ec5a778fb9a3e1e Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 18 Oct 2023 16:07:32 -0700 Subject: [PATCH] bcachefs: Refactor memcpy into direct assignment 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. Cc: Kent Overstreet Cc: Brian Foster Cc: linux-bcachefs@vger.kernel.org Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202309192314.VBsjiIm5-lkp@intel.com/ Link: https://lore.kernel.org/r/20231010235609.work.594-kees@kernel.org Signed-off-by: Kees Cook Signed-off-by: Kent Overstreet --- fs/bcachefs/extents.h | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/fs/bcachefs/extents.h b/fs/bcachefs/extents.h index 978ae5e7e8b1..879e7d218b6a 100644 --- a/fs/bcachefs/extents.h +++ b/fs/bcachefs/extents.h @@ -633,6 +633,8 @@ void bch2_bkey_extent_entry_drop(struct bkey_i *, union bch_extent_entry *); static inline void bch2_bkey_append_ptr(struct bkey_i *k, struct bch_extent_ptr ptr) { + struct bch_extent_ptr *dest; + EBUG_ON(bch2_bkey_has_device(bkey_i_to_s(k), ptr.dev)); switch (k->k.type) { @@ -642,12 +644,8 @@ static inline void bch2_bkey_append_ptr(struct bkey_i *k, struct bch_extent_ptr EBUG_ON(bkey_val_u64s(&k->k) >= BKEY_EXTENT_VAL_U64s_MAX); ptr.type = 1 << BCH_EXTENT_ENTRY_ptr; - - unsafe_memcpy((void *) &k->v + bkey_val_bytes(&k->k), - &ptr, - sizeof(ptr), - "Our memcpy target is relative to a zero size array ," - "compiler bounds checking doesn't work here"); + dest = (struct bch_extent_ptr *)((void *) &k->v + bkey_val_bytes(&k->k)); + *dest = ptr; k->k.u64s++; break; default: