On Fri, Apr 29, 2022 at 10:27:11AM -0700, Randy Dunlap wrote:
> When the NTFS BOOT sectors_per_clusters field is > 0x80,
> it represents a shift value. First change its sign to positive
> and then make sure that the shift count is not too large.
> 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>
> ---
> fs/ntfs3/super.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> --- linux-next-20220428.orig/fs/ntfs3/super.c
> +++ linux-next-20220428/fs/ntfs3/super.c
> @@ -670,7 +670,8 @@ static u32 true_sectors_per_clst(const s
> {
> return boot->sectors_per_clusters <= 0x80
> ? boot->sectors_per_clusters
> - : (1u << (0 - boot->sectors_per_clusters));
> + : -(s8)boot->sectors_per_clusters > 31 ? -1
> + : (1u << -(s8)boot->sectors_per_clusters);
> }
This hurts my brain. Can we do instead:
if (boot->sectors_per_clusters <= 0x80)
return boot->sectors_per_clusters;
if (boot->sectors_per_clusters < 0xA0)
return 1U << (boot->sectors_per_clusters - 0x80);
return -1;
> /*
> @@ -713,7 +714,7 @@ static int ntfs_init_from_boot(struct su
>
> /* cluster size: 512, 1K, 2K, 4K, ... 2M */
> sct_per_clst = true_sectors_per_clst(boot);
> - if (!is_power_of_2(sct_per_clst))
> + if ((int)sct_per_clst < 0 || !is_power_of_2(sct_per_clst))
> goto out;
Do we need this change? Presumably -1 is not a power of 2 ...
