Re: [PATCH 4.9 37/95] ext4: add validity checks for bitmap block numbers

[Theodore Y. Ts'o]

On Sun, Apr 22, 2018 at 10:54:23PM +0100, Ben Hutchings wrote:
> >  	offset = blk - group_first_block;
> > -	if (!ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
> > +	if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
> > +	    !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
> 
> Isn't sb->s_blocksize a count of bytes?  If so, doesn't that mean that
> we should be comparing with sb->s_blocksize * 8?

Yes, nice catch, Ben!  Can we temporarily drop this patch from the
stable queue until I can get a fix in?

In practice this shouldn't be a problem because of the default ext4
layout with flex_bg.  But we should definitely get this fixed before
we let this flow into the stable kernel.

       	    	      	  	 - Ted