RE: [PATCH] exfat: tighten down num_fats check

[Namjae Jeon]

> 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@xxxxxx>
> 
> --- 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!
> 
> 
> 
>