[PATCH v2 3/4] mm: BUG_ON to avoid NULL deference while __GFP_NOFAIL fails

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

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.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 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 c700d2598a26..cc179c3e68df 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4708,8 +4708,10 @@ 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 0ff5898cc6de..bad3258523b6 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);
 		WARN_ON_ONCE(!(flags & __GFP_NOWARN));
 		return NULL;
 	}
-- 
2.34.1