[PATCH] mtd: phram: Prevent divide by zero bug in phram_setup()

[Dan Carpenter]

On Fri, Jan 21, 2022 at 12:17:48PM +0100, Miquel Raynal wrote:
> Hi Dan,
> 
> dan.carpenter at oracle.com wrote on Fri, 21 Jan 2022 08:38:36 +0300:
> 
> > The problem is that "erasesize" is a uint32_t type so it might be
> 
> Don't you mean uint64_t here? Otherwise I don't get the sentence.
> 

Yeah.  I meant uint64_t.  Will resend.


> > non-zero but the truncated "(uint32_t)erasesize" value *is* zero. That
> 
> s/*is*/*can* be/ ? (again, if my understanding is correct).
> 

It might be a situation where "erasesize" is non-zero but after we
truncated it "(uint32_t)erasesize" is zero.

> > would lead to the divide by zero bug.
> > 
> > Avoid the bug by delaying the divide until after we have validated
> > that "erasesize" is reasonable.
> 
> I don't really get the fix. If "erasesize" is big enough, then
> (uint32_t)erasesize can however be zero. But checking if erasesize is
> zero beforehands does not fix the situation. Or am I missing
> something?

It doesn't just check for zero, it checks a couple other things
including  if erasesize > UINT_MAX.

regards,
dan carpenter