mainline build failure due to 0a97953fd221 ("lib: add bitmap_{from,to}_arr64")

Hi All,

The latest mainline kernel branch fails to build for "arm allmodconfig" and "csky allmodconfig".

"arm allmodconfig" fails with the error:

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/mutex.h:17,
                 from ./include/linux/rfkill.h:35,
                 from net/bluetooth/hci_core.c:29:

In function 'fortify_memcpy_chk',
inlined from 'bitmap_copy' at ./include/linux/bitmap.h:254:2,
inlined from 'bitmap_copy_clear_tail' at ./include/linux/bitmap.h:263:2,
inlined from 'bitmap_from_u64' at ./include/linux/bitmap.h:540:2,
inlined from 'hci_bdaddr_list_add_with_flags' at net/bluetooth/hci_core.c:2156:2:
./include/linux/fortify-string.h:344:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
344 | __write_overflow_field(p_size_field, size);

And, "csky allmodconfig" fails with the error:

In file included from ./include/linux/cpumask.h:12,

                 from ./include/linux/mm_types_task.h:14,
                 from ./include/linux/mm_types.h:5,
                 from ./include/linux/buildid.h:5,
                 from ./include/linux/module.h:14,
                 from net/bluetooth/mgmt.c:27:

In function 'bitmap_copy',
inlined from 'bitmap_copy_clear_tail' at ./include/linux/bitmap.h:263:2,
inlined from 'bitmap_from_u64' at ./include/linux/bitmap.h:540:2,
inlined from 'set_device_flags' at net/bluetooth/mgmt.c:4534:4:
./include/linux/bitmap.h:254:9: error: 'memcpy' forming offset [4, 7] is out of the bounds [0, 4] of object 'flags' with type 'long unsigned int[1]' [-Werror=array-bounds]

  254 |         memcpy(dst, src, len);
      |         ^~~~~~~~~~~~~~~~~~~~~
In file included from ./include/linux/kasan-checks.h:5,
                 from ./include/asm-generic/rwonce.h:26,
                 from ./arch/csky/include/generated/asm/rwonce.h:1,
                 from ./include/linux/compiler.h:248,
                 from ./include/linux/build_bug.h:5,
                 from ./include/linux/container_of.h:5,
                 from ./include/linux/list.h:5,
                 from ./include/linux/module.h:12,
                 from net/bluetooth/mgmt.c:27:

net/bluetooth/mgmt.c: In function 'set_device_flags':
net/bluetooth/mgmt.c:4532:40: note: 'flags' declared here
4532 | DECLARE_BITMAP(flags, __HCI_CONN_NUM_FLAGS);
| ^~~~~
./include/linux/types.h:11:23: note: in definition of macro 'DECLARE_BITMAP'
11 | unsigned long name[BITS_TO_LONGS(bits)]

For both the failures, git bisect points to:
0a97953fd221 ("lib: add bitmap_{from,to}_arr64")

And, reverting it on top of mainline branch has fixed both the build failures.

--
Regards
Sudip

Hi Sudip,

Thanks for pointing at this.

In the patch you mentioned, silent typecasting from to u64 has been replaced with explicit memory dereference, and it spotted -Warray-bounds:

static inline void bitmap_from_u64(unsigned long *dst, u64 mask) {
- dst[0] = mask & ULONG_MAX;
-
- if (sizeof(mask) > sizeof(unsigned long))
- dst[1] = mask >> 32;
+ bitmap_from_arr64(dst, &mask, 64);
}

The problem is that bluetooth code declares current_flags as u32, and later applies 64-bit function to convert it to bitmap.

In the bluetooth code, using bitmap_from_u64 is incorrect because of that, and because the length of bitmap in that case is __HCI_CONN_NUM_FLAGS, which is 2, not 64. The simplest fix is to switch to bitmap_from_arr32.

I'll send a fix shortly.

Thanks,
Yury