read(2) and thus bsdiff is limited to 2^31 bytes

[Joerg Sonnenberger]

On Mon, May 23, 2016 at 02:09:42AM +0300, Konstantin Belousov wrote:
> On Sun, May 22, 2016 at 03:56:33PM -0700, Conrad Meyer wrote:
> > On Sun, May 22, 2016 at 1:54 PM, Dirk Engling <erdgeist at erdgeist.org> wrote:
> > > When trying to bsdiff two DVD images, I noticed it failing due to
> > > read(2) returning EINVAL to the tool. man 2 read says, this would only
> > > happen for a negative value for fildes, which clearly was not true.
> > 
> > Actually, it's documented at the very bottom of the first section:
> > 
> > ERRORS
> >      The read(), readv(), pread() and preadv() system calls will succeed
> >      unless:
> > ...
> >      [EINVAL]           The value nbytes is greater than INT_MAX.
> > 
> > It does seem silly to me given nbytes is a size_t.  I think it should
> > error if nbytes is greater than SSIZE_T_MAX, but on platforms where
> > size_t is larger than int (e.g. amd64) it shouldn't error for nbytes
> > in [INT_MAX, SSIZE_T_MAX - 1].
> It does not look silly to me, due to the typical
> 	if (read() < 0)
> checks in the code.  Even
> 	if (read() == -1)
> is vulnerable.

But that code can already fail in a number of situations. Short reads as
well as short writes can happen in any of a number of situations.

Joerg