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

[Hyeonggon Yoo]

On Fri, Sep 23, 2022 at 01:28:07PM -0700, Kees Cook wrote:
> 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@xxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  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
> 

This is now squashed with later one. (so undefined __alloc_size__ issues are fixed)
for the latest version of this patch:

Looks good to me,
Acked-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

-- 
Thanks,
Hyeonggon