On Fri, Oct 04, 2024 at 05:52:10PM +0800, Vlastimil Babka wrote:
> On 10/4/24 11:18, Vlastimil Babka wrote:
> > On 10/4/24 08:44, Marco Elver wrote:
> >
> > I think it's commit d0a38fad51cc7 doing in __do_krealloc()
> >
> > - ks = ksize(p);
> > +
> > + s = virt_to_cache(p);
> > + orig_size = get_orig_size(s, (void *)p);
> > + ks = s->object_size;
> >
> > so for kfence objects we don't get their actual allocation size but the
> > potentially larger bucket size?
> >
> > I guess we could do:
> >
> > ks = kfence_ksize(p) ?: s->object_size;
> >
> > ?
>
> Hmm this probably is not the whole story, we also have:
>
> - memcpy(ret, kasan_reset_tag(p), ks);
> + if (orig_size)
> + memcpy(ret, kasan_reset_tag(p), orig_size);
>
> orig_size for kfence will be again s->object_size so the memcpy might be a
> (read) buffer overflow from a kfence allocation.
>
> I think get_orig_size() should perhaps return kfence_ksize(p) for kfence
> allocations, in addition to the change above.
>
> Or alternatively we don't change get_orig_size() (in a different commit) at
> all, but __do_krealloc() will have an "if is_kfence_address()" that sets
> both orig_size and ks to kfence_ksize(p) appropriately. That might be easier
> to follow.
Thanks for the suggestion!
As there were error report about the NULL slab for big kmalloc object, how
about the following code for
__do_krealloc(const void *p, size_t new_size, gfp_t flags)
{
void *ret;
size_t ks = 0;
int orig_size = 0;
struct kmem_cache *s = NULL;
/* Check for double-free. */
if (likely(!ZERO_OR_NULL_PTR(p))) {
if (!kasan_check_byte(p))
return NULL;
ks = ksize(p);
/* Some objects have no orig_size, like big kmalloc case */
if (is_kfence_address(p)) {
orig_size = kfence_ksize(p);
} else if (virt_to_slab(p)) {
s = virt_to_cache(p);
orig_size = get_orig_size(s, (void *)p);
}
} else {
goto alloc_new;
}
/* If the object doesn't fit, allocate a bigger one */
if (new_size > ks)
goto alloc_new;
/* Zero out spare memory. */
if (want_init_on_alloc(flags)) {
kasan_disable_current();
if (orig_size && orig_size < new_size)
memset((void *)p + orig_size, 0, new_size - orig_size);
else
memset((void *)p + new_size, 0, ks - new_size);
kasan_enable_current();
}
/* Setup kmalloc redzone when needed */
if (s && slub_debug_orig_size(s) && !is_kfence_address(p)) {
set_orig_size(s, (void *)p, new_size);
if (s->flags & SLAB_RED_ZONE && new_size < ks)
memset_no_sanitize_memory((void *)p + new_size,
SLUB_RED_ACTIVE, ks - new_size);
}
p = kasan_krealloc((void *)p, new_size, flags);
return (void *)p;
alloc_new:
ret = kmalloc_node_track_caller_noprof(new_size, flags, NUMA_NO_NODE, _RET_IP_);
if (ret && p) {
/* Disable KASAN checks as the object's redzone is accessed. */
kasan_disable_current();
memcpy(ret, kasan_reset_tag(p), orig_size ?: ks);
kasan_enable_current();
}
return ret;
}
I've run it with the reproducer of syzbot, so far the issue hasn't been
reproduced on my local machine.
Thanks,
Feng
>
> But either way means rewriting 2 commits. I think it's indeed better to drop
> the series now from -next and submit a v3.
>
> Vlastimil
>
> >> Thanks,
> >> -- Marco
> >
>
