[PATCH v2 01/16] slab: Remove __malloc attribute from realloc functions

Kees Cook
2022-09-23T20:32:53Z

The __malloc attribute should not be applied to "realloc" functions, as
the returned pointer may alias the storage of the prior pointer. Instead
of splitting __malloc from __alloc_size, which would be a huge amount of
churn, just create __realloc_size for the few cases where it is needed.

Additionally removes the conditional test for __alloc_size__, which is
always defined now.

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: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: linux-mm@kvack.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/compiler_types.h | 13 +++++--------
include/linux/slab.h | 12 ++++++------
mm/slab_common.c | 4 ++--
3 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 4f2a819fd60a..f141a6f6b9f6 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -271,15 +271,12 @@ struct ftrace_likely_data {

/*
* Any place that could be marked with the "alloc_size" attribute is also
- * a place to be marked with the "malloc" attribute. Do this as part of the
- * __alloc_size macro to avoid redundant attributes and to avoid missing a
- * __malloc marking.
+ * a place to be marked with the "malloc" attribute, except those that may
+ * be performing a _reallocation_, as that may alias the existing pointer.
+ * For these, use __realloc_size().
*/
-#ifdef __alloc_size__
-# define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
-#else
-# define __alloc_size(x, ...) __malloc
-#endif
+#define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
+#define __realloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__)

#ifndef asm_volatile_goto
#define asm_volatile_goto(x...) asm goto(x)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 0fefdf528e0d..41bd036e7551 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -184,7 +184,7 @@ int kmem_cache_shrink(struct kmem_cache *s);
/*
* Common kmalloc functions provided by all allocators
*/
-void * __must_check krealloc(const void *objp, size_t new_size, gfp_t flags) __alloc_size(2);
+void * __must_check krealloc(const void *objp, size_t new_size, gfp_t flags) __realloc_size(2);
void kfree(const void *objp);
void kfree_sensitive(const void *objp);
size_t __ksize(const void *objp);
@@ -647,10 +647,10 @@ static inline __alloc_size(1, 2) void *kmalloc_array(size_t n, size_t size, gfp_
* @new_size: new size of a single member of the array
* @flags: the type of memory to allocate (see kmalloc)
*/
-static inline __alloc_size(2, 3) void * __must_check krealloc_array(void *p,
- size_t new_n,
- size_t new_size,
- gfp_t flags)
+static inline __realloc_size(2, 3) void * __must_check krealloc_array(void *p,
+ size_t new_n,
+ size_t new_size,
+ gfp_t flags)
{
size_t bytes;

@@ -774,7 +774,7 @@ static inline __alloc_size(1, 2) void *kvcalloc(size_t n, size_t size, gfp_t fla
}

extern void *kvrealloc(const void *p, size_t oldsize, size_t newsize, gfp_t flags)
- __alloc_size(3);
+ __realloc_size(3);
extern void kvfree(const void *addr);
extern void kvfree_sensitive(const void *addr, size_t len);

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 17996649cfe3..457671ace7eb 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1134,8 +1134,8 @@ module_init(slab_proc_init);

#endif /* CONFIG_SLAB || CONFIG_SLUB_DEBUG */

-static __always_inline void *__do_krealloc(const void *p, size_t new_size,
- gfp_t flags)
+static __always_inline __realloc_size(2) void *
+__do_krealloc(const void *p, size_t new_size, gfp_t flags)
{
void *ret;
size_t ks;
--
2.34.1