Re: [PATCH v2] Handle NULL input to malloc_usable_size [BZ #28506]

["Richard W.M. Jones" <rjones@redhat.com>]

On Fri, Oct 29, 2021 at 02:25:21PM +0530, Siddhesh Poyarekar wrote:
> Hoist the NULL check for malloc_usable_size into its entry points in
> malloc-debug and malloc and assume non-NULL in all callees.  This fixes
> BZ #28506
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> ---
>  malloc/malloc-debug.c      | 12 ++++++------
>  malloc/malloc.c            | 24 ++++++++----------------
>  malloc/tst-malloc-usable.c | 21 ++++++++-------------
>  3 files changed, 22 insertions(+), 35 deletions(-)
> 
> diff --git a/malloc/malloc-debug.c b/malloc/malloc-debug.c
> index 9922ef5f25..5e954d7dc2 100644
> --- a/malloc/malloc-debug.c
> +++ b/malloc/malloc-debug.c
> @@ -399,17 +399,17 @@ strong_alias (__debug_calloc, calloc)
>  size_t
>  malloc_usable_size (void *mem)
>  {
> +  if (mem == NULL)
> +    return 0;
> +
>    if (__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK))
>      return mcheck_usable_size (mem);
>    if (__is_malloc_debug_enabled (MALLOC_CHECK_HOOK))
>      return malloc_check_get_size (mem);
>  
> -  if (mem != NULL)
> -    {
> -      mchunkptr p = mem2chunk (mem);
> -     if (DUMPED_MAIN_ARENA_CHUNK (p))
> -       return chunksize (p) - SIZE_SZ;
> -    }
> +  mchunkptr p = mem2chunk (mem);
> +  if (DUMPED_MAIN_ARENA_CHUNK (p))
> +    return chunksize (p) - SIZE_SZ;
>  
>    return musable (mem);
>  }
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 2ba1fee144..a9dfc82788 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -5007,20 +5007,13 @@ __malloc_trim (size_t s)
>  static size_t
>  musable (void *mem)
>  {
> -  mchunkptr p;
> -  if (mem != 0)
> -    {
> -      size_t result = 0;
> -
> -      p = mem2chunk (mem);
> +  mchunkptr p = mem2chunk (mem);
>  
> -      if (chunk_is_mmapped (p))
> -	result = chunksize (p) - CHUNK_HDR_SZ;
> -      else if (inuse (p))
> -	result = memsize (p);
> +  if (chunk_is_mmapped (p))
> +    return chunksize (p) - CHUNK_HDR_SZ;
> +  else if (inuse (p))
> +    return memsize (p);
>  
> -      return result;
> -    }
>    return 0;
>  }
>  
> @@ -5028,10 +5021,9 @@ musable (void *mem)
>  size_t
>  __malloc_usable_size (void *m)
>  {
> -  size_t result;
> -
> -  result = musable (m);
> -  return result;
> +  if (m == NULL)
> +    return 0;
> +  return musable (m);
>  }
>  #endif
>  
> diff --git a/malloc/tst-malloc-usable.c b/malloc/tst-malloc-usable.c
> index a1074b782a..e50cadcf10 100644
> --- a/malloc/tst-malloc-usable.c
> +++ b/malloc/tst-malloc-usable.c
> @@ -21,29 +21,24 @@
>  #include <malloc.h>
>  #include <string.h>
>  #include <stdio.h>
> +#include <support/support.h>
> +#include <support/check.h>
>  
>  static int
>  do_test (void)
>  {
>    size_t usable_size;
>    void *p = malloc (7);
> -  if (!p)
> -    {
> -      printf ("memory allocation failed\n");
> -      return 1;
> -    }
>  
> +  TEST_VERIFY_EXIT (p != NULL);
>    usable_size = malloc_usable_size (p);
> -  if (usable_size != 7)
> -    {
> -      printf ("malloc_usable_size: expected 7 but got %zu\n", usable_size);
> -      return 1;
> -    }
> -
> +  TEST_COMPARE (usable_size, 7);
>    memset (p, 0, usable_size);
>    free (p);
> +
> +  TEST_COMPARE (malloc_usable_size (NULL), 0);
> +
>    return 0;
>  }
>  
> -#define TEST_FUNCTION do_test ()
> -#include "../test-skeleton.c"
> +#include "support/test-driver.c"

Also looks sensible, so:

Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

Rich.

-- 
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