[Bug malloc/28506] New: malloc-check + malloc_usage_size(NULL) causes segfault

["rjones at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28506

            Bug ID: 28506
           Summary: malloc-check + malloc_usage_size(NULL) causes segfault
           Product: glibc
           Version: 2.35
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
          Assignee: unassigned at sourceware dot org
          Reporter: rjones at redhat dot com
  Target Milestone: ---

glibc-2.34.9000-15.fc36.x86_64

According to the documentation, malloc_usage_size(NULL) is valid
and should return 0, and indeed that is how the ordinary function
behaves.

However when I enable malloc-check, it segfaults instead.

Test program:

------------
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>

int
main (void)
{
  void *ptr = malloc (511);
  printf ("malloc_usable_size(ptr) = %zu\n",
          malloc_usable_size (ptr));
  printf ("malloc_usable_size(NULL) = %zu\n",
          malloc_usable_size (NULL));
  return 0;
}
------------

Output:

$ LD_PRELOAD=libc_malloc_debug.so.0 GLIBC_TUNABLES='glibc.malloc.check=1'
./malloc_usable_size
malloc_usable_size(ptr) = 511
Segmentation fault (core dumped)

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