2022-04-30 5:01 GMT+09:00, Randy Dunlap <rdunlap@xxxxxxxxxxxxx>:
> When the NTFS BOOT sectors_per_clusters field is > 0x80,
> it represents a shift value. Make sure that the shift value is
> not too large (> 31) before using it. Return 0xffffffff if it is.
>
> This prevents negative shift values and shift values that are
> larger than the field size.
>
> Prevents this UBSAN error:
>
> UBSAN: shift-out-of-bounds in ../fs/ntfs3/super.c:673:16
> shift exponent -192 is negative
>
> Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
> Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Reported-by: syzbot+1631f09646bc214d2e76@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Konstantin Komarov <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>
> Cc: ntfs3@xxxxxxxxxxxxxxx
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Kari Argillander <kari.argillander@xxxxxxxxxxxxxxxxxxxx>
> Cc: Namjae Jeon <linkinjeon@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> ---
> v2: use Willy's suggestions
>
> fs/ntfs3/super.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> --- linux-next-20220428.orig/fs/ntfs3/super.c
> +++ linux-next-20220428/fs/ntfs3/super.c
> @@ -668,9 +668,11 @@ static u32 format_size_gb(const u64 byte
>
> static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
> {
> - return boot->sectors_per_clusters <= 0x80
> - ? boot->sectors_per_clusters
> - : (1u << (0 - boot->sectors_per_clusters));
> + if (boot->sectors_per_clusters <= 0x80)
> + return boot->sectors_per_clusters;
> + if (boot->sectors_per_clusters > 0xe0) /* limit to 31-bit shift */
ntfs maximum cluster size is 2MB. I think that we can change it to
boot->sectors_per_clusters >= 0xf4.
> + return 1U << (0 - boot->sectors_per_clusters);
> + return 0xffffffff;
It would be better to change it to return an error(-EINVAL) instead of
0xffffffff.
and if sct_per_clst < 0, goto out immediately..
> }
>
> /*
>
>
