[PATCH v2 2/2] mm/slub: extend redzone check to cover all allocated kmalloc space

[Feng Tang]

kmalloc will round up the request size to a fixes size (mostly power
of 2), so there could be a extra space than what user request, whose
size is the actual buffer size minus original request size.

To better detect out of bound access or abuse of this space, add
redzone sannity check for it.

And in current kernel, some kmalloc user already knows the existence
of the space and utilize it after calling 'ksize()' to know the real
size of the allocated buffer. So we skip the sanity check for objects
which have been called with ksize(), as treating them as legitimate
users.

Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
Hi reviewers,

I'm not sure if I should carve out the legitimizing ksize() check
and kzalloc() zeroing buffer to separate ones, and just put them
together as one patch. pls let me know if you think this should be
separated.

Thanks,
Feng

 mm/slab.c |  8 ++++----
 mm/slab.h |  9 +++++++--
 mm/slub.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 57 insertions(+), 13 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index f8cd00f4ba13..9501510c3940 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3236,7 +3236,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, size_t orig_
 	init = slab_want_init_on_alloc(flags, cachep);
 
 out_hooks:
-	slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr, init);
+	slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr, init, 0);
 	return ptr;
 }
 
@@ -3299,7 +3299,7 @@ slab_alloc(struct kmem_cache *cachep, struct list_lru *lru, gfp_t flags,
 	init = slab_want_init_on_alloc(flags, cachep);
 
 out:
-	slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init);
+	slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init, 0);
 	return objp;
 }
 
@@ -3546,13 +3546,13 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	 * Done outside of the IRQ disabled section.
 	 */
 	slab_post_alloc_hook(s, objcg, flags, size, p,
-				slab_want_init_on_alloc(flags, s));
+				slab_want_init_on_alloc(flags, s), 0);
 	/* FIXME: Trace call missing. Christoph would like a bulk variant */
 	return size;
 error:
 	local_irq_enable();
 	cache_alloc_debugcheck_after_bulk(s, flags, i, p, _RET_IP_);
-	slab_post_alloc_hook(s, objcg, flags, i, p, false);
+	slab_post_alloc_hook(s, objcg, flags, i, p, false, 0);
 	__kmem_cache_free_bulk(s, i, p);
 	return 0;
 }
diff --git a/mm/slab.h b/mm/slab.h
index db9fb5c8dae7..806822c78d24 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -733,12 +733,17 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
 
 static inline void slab_post_alloc_hook(struct kmem_cache *s,
 					struct obj_cgroup *objcg, gfp_t flags,
-					size_t size, void **p, bool init)
+					size_t size, void **p, bool init,
+					unsigned int orig_size)
 {
 	size_t i;
 
 	flags &= gfp_allowed_mask;
 
+	/* If original request size(kmalloc) is not set, use object_size */
+	if (!orig_size)
+		orig_size = s->object_size;
+
 	/*
 	 * As memory initialization might be integrated into KASAN,
 	 * kasan_slab_alloc and initialization memset must be
@@ -749,7 +754,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
 	for (i = 0; i < size; i++) {
 		p[i] = kasan_slab_alloc(s, p[i], flags, init);
 		if (p[i] && init && !kasan_has_integrated_init())
-			memset(p[i], 0, s->object_size);
+			memset(p[i], 0, orig_size);
 		kmemleak_alloc_recursive(p[i], s->object_size, 1,
 					 s->flags, flags);
 	}
diff --git a/mm/slub.c b/mm/slub.c
index 9763a38bc4f0..8f3314f0725d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -193,8 +193,8 @@ static inline bool kmem_cache_debug(struct kmem_cache *s)
 
 static inline bool slub_debug_orig_size(struct kmem_cache *s)
 {
-	return (s->flags & SLAB_KMALLOC &&
-			kmem_cache_debug_flags(s, SLAB_STORE_USER));
+	return (kmem_cache_debug_flags(s, SLAB_STORE_USER | SLAB_RED_ZONE) &&
+			(s->flags & SLAB_KMALLOC));
 }
 
 void *fixup_red_left(struct kmem_cache *s, void *p)
@@ -838,6 +838,11 @@ static inline void set_orig_size(struct kmem_cache *s,
 	*(unsigned int *)p = orig_size;
 }
 
+static inline void skip_orig_size_check(struct kmem_cache *s, const void *object)
+{
+	set_orig_size(s, (void *)object, s->object_size);
+}
+
 static unsigned int get_orig_size(struct kmem_cache *s, void *object)
 {
 	void *p = kasan_reset_tag(object);
@@ -970,13 +975,28 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
 static void init_object(struct kmem_cache *s, void *object, u8 val)
 {
 	u8 *p = kasan_reset_tag(object);
+	unsigned int orig_size = s->object_size;
 
 	if (s->flags & SLAB_RED_ZONE)
 		memset(p - s->red_left_pad, val, s->red_left_pad);
 
+	if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) {
+		unsigned int zone_start;
+
+		orig_size = get_orig_size(s, object);
+		zone_start = orig_size;
+
+		if (!freeptr_outside_object(s))
+			zone_start = max_t(unsigned int, orig_size, s->offset + sizeof(void *));
+
+		/* Redzone the allocated by kmalloc but unused space */
+		if (zone_start < s->object_size)
+			memset(p + zone_start, val, s->object_size - zone_start);
+	}
+
 	if (s->flags & __OBJECT_POISON) {
-		memset(p, POISON_FREE, s->object_size - 1);
-		p[s->object_size - 1] = POISON_END;
+		memset(p, POISON_FREE, orig_size - 1);
+		p[orig_size - 1] = POISON_END;
 	}
 
 	if (s->flags & SLAB_RED_ZONE)
@@ -1122,6 +1142,7 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
 {
 	u8 *p = object;
 	u8 *endobject = object + s->object_size;
+	unsigned int orig_size;
 
 	if (s->flags & SLAB_RED_ZONE) {
 		if (!check_bytes_and_report(s, slab, object, "Left Redzone",
@@ -1139,6 +1160,20 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
 		}
 	}
 
+	if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) {
+		orig_size = get_orig_size(s, object);
+
+		if (!freeptr_outside_object(s))
+			orig_size = max_t(unsigned int, orig_size,
+						s->offset + sizeof(void *));
+		if (s->object_size > orig_size  &&
+			!check_bytes_and_report(s, slab, object,
+				"kmalloc unused part", p + orig_size,
+				val, s->object_size - orig_size)) {
+			return 0;
+		}
+	}
+
 	if (s->flags & SLAB_POISON) {
 		if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON) &&
 			(!check_bytes_and_report(s, slab, p, "Poison", p,
@@ -3287,7 +3322,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct list_l
 	init = slab_want_init_on_alloc(gfpflags, s);
 
 out:
-	slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init);
+	slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init, orig_size);
 
 	return object;
 }
@@ -3802,11 +3837,11 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	 * Done outside of the IRQ disabled fastpath loop.
 	 */
 	slab_post_alloc_hook(s, objcg, flags, size, p,
-				slab_want_init_on_alloc(flags, s));
+				slab_want_init_on_alloc(flags, s), 0);
 	return i;
 error:
 	slub_put_cpu_ptr(s->cpu_slab);
-	slab_post_alloc_hook(s, objcg, flags, i, p, false);
+	slab_post_alloc_hook(s, objcg, flags, i, p, false, 0);
 	__kmem_cache_free_bulk(s, i, p);
 	return 0;
 }
@@ -4611,6 +4646,10 @@ size_t __ksize(const void *object)
 	if (unlikely(!folio_test_slab(folio)))
 		return folio_size(folio);
 
+#ifdef CONFIG_SLUB_DEBUG
+	skip_orig_size_check(folio_slab(folio)->slab_cache, object);
+#endif
+
 	return slab_ksize(folio_slab(folio)->slab_cache);
 }
 EXPORT_SYMBOL(__ksize);
-- 
2.27.0