RE: [PATCH] exfat: tighten down num_fats check

Namjae Jeon
2020-02-17T00:38:07Z

> Change the test for num_fats from != 0 to a check for specifically 1.
>
> Although it's theoretically possible that num_fats == 2 for a TexFAT
> volume (or an implementation that doesn't do the full TexFAT but does
> support 2 FAT tables), the rest of the code doesn't currently DTRT if it's
> 2 (in particular, not handling the case of ActiveFat pointing at the
> second FAT area), so we'll disallow that as well, as well as dealing with
> corrupted images that have a trash non-zero value.
>
> Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
>
> --- a/fs/exfat/super.c 2020-02-14 17:45:02.262274632 -0500
> +++ b/fs/exfat/super.c 2020-02-14 17:46:37.200343723 -0500
> @@ -450,7 +450,7 @@ static int __exfat_fill_super(struct sup
> }
>
> p_bpb = (struct pbr64 *)p_pbr;
> - if (!p_bpb->bsx.num_fats) {
> + if (p_bpb->bsx.num_fats != 1) {
> exfat_msg(sb, KERN_ERR, "bogus number of FAT structure");
Could you please update error message for the reason why num_fats is allowed
only 1?
> ret = -EINVAL;
> goto free_bh;
Let's remove exfat_mirror_bh(), FAT2_start_sector variable and the below
related codes together.

sbi->FAT2_start_sector = p_bpb->bsx.num_fats == 1 ?
sbi->FAT1_start_sector :
sbi->FAT1_start_sector + sbi->num_FAT_sectors;

Thanks for your patch!
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