[PATCH v2] stdlib: random_r: fix unaligned access in initstate and initstate_r [BZ #30584]

[Andreas K. Huettel]

> 
> Sorry for not catching this before.  I'm kind of surpised that &b[idx]
> doesn't assert that b is already 4-byte aligned.  There is also a
> pointer wraparound issue here because read_state/write_state get called
> with -1, which is now converted to ~(size_t) 0.  So perhaps use “int idx”
> and write:
> 
>   /* Use literal 4 to avoid conversion to an unsigned type and pointer
>      wraparound.  */
>   memcpy ((char *) b + idx * 4, &v, 4);
> 
> (I think C is a bit ambiguous whether &b[idx] actually qualifies as
> access.)
> 
> The int32_t types are part of the public API, so those are kind of hard
> to avoid.  We could memcpy into those pointers, too, but if this more
> limited approach works, then I suppose that's okay.
> 
> 
> > +static int
> > +do_test (void)
> > +{
> > +  struct random_data rand_state = { .state = NULL };
> > +  _Alignas (double) char buf[128 + sizeof (int32_t)];
> > +
> > +  /* Test initstate_r with an unaligned `state` array.  */
> > +  initstate_r (time (NULL), buf + 1, sizeof buf, &rand_state);
> > +
> > +  /* Ditto initstate.  */
> > +  initstate (time (NULL), buf + 1, sizeof buf);
> > +
> > +  return 0;
> > +}
> 
> Looks okay now.

Then let's add it for 2.41 ... -a

> 
> Thanks,
> Florian
> 
> 


-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer 
(council, comrel, toolchain, base-system, perl, libreoffice)
https://wiki.gentoo.org/wiki/User:Dilfridge
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