[PATCH 11/12] slab: Remove __malloc attribute from realloc functions

Kees Cook
2022-09-22T03:10:32Z

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: 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: Nick Desaulniers <ndesaulniers@google.com>
Cc: Hao Luo <haoluo@google.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 ++++++------
2 files changed, 11 insertions(+), 14 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 4fc41e4ed4a2..ac3832b50dbb 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);
@@ -661,10 +661,10 @@ 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;

@@ -788,7 +788,7 @@ 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);

--
2.34.1