Re: [PATCH v3] fs/ntfs3: validate BOOT sectors_per_clusters

[Namjae Jeon <linkinjeon@kernel.org>]

2022-05-03 2:53 GMT+09:00, Randy Dunlap <rdunlap@infradead.org>:
> 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 before using it (NTFS max cluster size is 2MB).
> Return -EVINVAL if it 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@infradead.org>
> Reported-by: syzbot+1631f09646bc214d2e76@syzkaller.appspotmail.com
> Cc: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
> Cc: ntfs3@lists.linux.dev
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kari Argillander <kari.argillander@stargateuniverse.net>
> Cc: Namjae Jeon <linkinjeon@kernel.org>
> Cc: Matthew Wilcox <willy@infradead.org>
Looks good to me:)

Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>

Thanks.
> ---
> v2: use Willy's suggestions
> v3: use Namjae's suggestions -- but now Konstantin can decide.
>     drop Willy's Rev-by: tag due to changes
>
>  fs/ntfs3/super.c |   10 +++++++---
>  1 file changed, 7 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 >= 0xf4) /* limit shift to 2MB max */
> +		return 1U << (0 - boot->sectors_per_clusters);
> +	return -EINVAL;
>  }
>
>  /*
> @@ -713,6 +715,8 @@ static int ntfs_init_from_boot(struct su
>
>  	/* cluster size: 512, 1K, 2K, 4K, ... 2M */
>  	sct_per_clst = true_sectors_per_clst(boot);
> +	if ((int)sct_per_clst < 0)
> +		goto out;
>  	if (!is_power_of_2(sct_per_clst))
>  		goto out;
>
>
>