Looks like bfp has a set of macro suitable for such cases:
#define BITS_PER_BYTE_MASKED(bits) ((bits) & BITS_PER_BYTE_MASK)
#define BITS_ROUNDDOWN_BYTES(bits) ((bits) >> 3)
#define BITS_ROUNDUP_BYTES(bits) \
(BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
May be it makes sense to move them to a generic header and to use here?
--
Alexey Khoroshilov
On 26.03.2022 14:40, Fedor Pchelkin wrote:
> If count argument in copy_fd_bitmaps() is not a multiple of
> BITS_PER_BYTE, then one byte is lost and is not used in further
> manipulations with cpy value in memcpy() and memset()
> causing a leak. The leak was introduced with close_range() call
> using CLOSE_RANGE_UNSHARE flag.
>
> The patch suggests implementing an indicator (named add_byte)
> of count being multiple of BITS_PER_BYTE and adding it to the
> cpy value.
>
> Found by Syzkaller (https://github.com/google/syzkaller).
>
> Signed-off-by: Fedor Pchelkin <[email protected]>
> Signed-off-by: Alexey Khoroshilov <[email protected]>
> ---
> fs/file.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/fs/file.c b/fs/file.c
> index 3ef1479df203..3c64a6423604 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -56,10 +56,8 @@ static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
> {
> unsigned int cpy, set;
> unsigned int add_byte = 0;
> -
> if (count % BITS_PER_BYTE != 0)
> add_byte = 1;
> -
> cpy = count / BITS_PER_BYTE + add_byte;
> set = (nfdt->max_fds - count) / BITS_PER_BYTE;
> memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
>