On Mon, Aug 19, 2024 at 9:43 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 17.08.24 08:24, Barry Song wrote:
> > From: Barry Song <v-songbaohua@xxxxxxxx>
> >
> > We have cases we still fail though callers might have __GFP_NOFAIL. Since
> > they don't check the return, we are exposed to the security risks for NULL
> > deference.
> >
> > Though BUG_ON() is not encouraged by Linus, this is an unrecoverable
> > situation.
> >
> > Christoph Hellwig:
> > The whole freaking point of __GFP_NOFAIL is that callers don't handle
> > allocation failures. So in fact a straight BUG is the right thing
> > here.
> >
> > Vlastimil Babka:
> > It's just not a recoverable situation (WARN_ON is for recoverable
> > situations). The caller cannot handle allocation failure and at the same
> > time asked for an impossible allocation. BUG_ON() is a guaranteed oops
> > with stracktrace etc. We don't need to hope for the later NULL pointer
> > dereference (which might if really unlucky happen from a different
> > context where it's no longer obvious what lead to the allocation failing).
> >
> > Michal Hocko:
> > Linus tends to be against adding new BUG() calls unless the failure is
> > absolutely unrecoverable (e.g. corrupted data structures etc.). I am
> > not sure how he would look at simply incorrect memory allocator usage to
> > blow up the kernel. Now the argument could be made that those failures
> > could cause subtle memory corruptions or even be exploitable which might
> > be a sufficient reason to stop them early.
> >
> > Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> > Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Kees Cook <kees@xxxxxxxxxx>
> > Cc: "Eugenio Pérez" <eperezma@xxxxxxxxxx>
> > Cc: Hailong.Liu <hailong.liu@xxxxxxxx>
> > Cc: Jason Wang <jasowang@xxxxxxxxxx>
> > Cc: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
> > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> > Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > ---
> > include/linux/slab.h | 4 +++-
> > mm/page_alloc.c | 4 +++-
> > mm/util.c | 1 +
> > 3 files changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index c9cb42203183..4a4d1fdc2afe 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -827,8 +827,10 @@ kvmalloc_array_node_noprof(size_t n, size_t size, gfp_t flags, int node)
> > {
> > size_t bytes;
> >
> > - if (unlikely(check_mul_overflow(n, size, &bytes)))
> > + if (unlikely(check_mul_overflow(n, size, &bytes))) {
> > + BUG_ON(flags & __GFP_NOFAIL);
> > return NULL;
> > + }
> >
> > return kvmalloc_node_noprof(bytes, flags, node);
> > }
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 60742d057b05..d2c37f8f8d09 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4668,8 +4668,10 @@ struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order,
> > * There are several places where we assume that the order value is sane
> > * so bail out early if the request is out of bound.
> > */
> > - if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp))
> > + if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp)) {
> > + BUG_ON(gfp & __GFP_NOFAIL);
> > return NULL;
> > + }
> >
> > gfp &= gfp_allowed_mask;
> > /*
> > diff --git a/mm/util.c b/mm/util.c
> > index ac01925a4179..678c647b778f 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -667,6 +667,7 @@ void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
> >
> > /* Don't even allow crazy sizes */
> > if (unlikely(size > INT_MAX)) {
> > + BUG_ON(flags & __GFP_NOFAIL);
>
> No new BUG_ON please. WARN_ON_ONCE() + recovery code might be suitable here.
Hi David,
WARN_ON_ONCE() might be fine but I don't see how it is possible to recover.
>
> --
> Cheers,
>
> David / dhildenb
>
