Re: [PATCH 1/1] zram: reject disksizes that exceed slot index range

[Sergey Senozhatsky]

On (26/08/05 11:54), Andrew Morton wrote:
> > From: Longlong Xia <xialonglong@xxxxxxxxxx>
> > 
> > zram uses u32 slot indexes, while disksize_store() accepts a u64
> > size. On 32-bit systems, a disksize larger than U32_MAX pages is
> > truncated when zram_meta_alloc() assigns the page count to size_t.
> > array_size() then sees only the truncated count, so a small table can
> > be allocated while the original capacity is published. Valid I/O
> > within that capacity can subsequently access beyond zram->table.
> > 
> > The same oversized capacity also lets full-device scanners compare a
> > u32 index with an upper bound larger than U32_MAX, so the index can
> > wrap instead of terminating.
> > 
> > Reject disksizes larger than U32_MAX pages before aligning and
> > allocating the table. This keeps the table size, published capacity and
> > slot index range consistent.
> 
> Oh.  Rejecting large devices sounds severe.  Can't we just fix the
> 32-bit trucation issues?

zram historically used u32, I never thought that anyone would want
a 16TB+ device.  But we don't really have reasons to limit it.

I can look into converting to unsigned long, Longlong is already
looking into it.