Re: Synthetic symbol leak in in elf_x86_64_get_synthetic_symtab and elf_read_minimal_symbols

[Alex Lindsay <alexlindsay239@gmail.com>]

Thanks for looking into it!

On 08/11/2017 04:27 AM, Yao Qi wrote:
> On 17-08-07 10:19:15, Alex Lindsay wrote:
>> We perform a couple of  dynamic allocations in
>> elf_x86_64_get_synthetic_symtab (elf64-x86-64.c):
>>
>>    s = *ret = (asymbol *) bfd_zmalloc (size);
>>
>>    names = (char *) bfd_malloc (size);
>>
>> that appear to never get freed. My patch for this:
> Good catch!  It is more complicated that other bfd targets allocate
> memory for asymbol in a different way as if asymbol.name is defined
> as an zero-length array, so memory allocated for both asymbol and .name
> in one bfd_malloc call, like,
>
> 	  sym = *r->sym_ptr_ptr;
> 	  if (!sym_exists_at (syms, opdsymend, symcount,
> 			      sym->section->id, sym->value + r->addend))
> 	    {
> 	      ++count;
> 	      size += sizeof (asymbol);
> 	      size += strlen (syms[i]->name) + 2;
> 	    }
> 	}
>
>        if (size == 0)
> 	goto done;
>        s = *ret = bfd_malloc (size);
>
> or
>
>    size = count * sizeof (asymbol);
>    p = relplt->relocation;
>    for (i = 0; i < count; i++, p += elf32_arm_size_info.int_rels_per_ext_rel)
>      {
>        size += strlen ((*p->sym_ptr_ptr)->name) + sizeof ("@plt");
>        if (p->addend != 0)
> 	size += sizeof ("+0x") - 1 + 8;
>      }
>
>    s = *ret = (asymbol *) bfd_malloc (size);
>
>> diff --git a/gdb/elfread.c b/gdb/elfread.c
>> index ece704ca7c..5ed8a6f957 100644
>> --- a/gdb/elfread.c
>> +++ b/gdb/elfread.c
>> @@ -1144,6 +1144,9 @@ elf_read_minimal_symbols (struct objfile *objfile, int
>> symfile_flags,
>>
>>     if (symtab_create_debug)
>>       fprintf_unfiltered (gdb_stdlog, "Done reading minimal symbols.\n");
>> +  if (synthcount > 0)
>> +    xfree ((char *) synthsyms->name);
> We can't do this for some bfd targets.
>
>> +  xfree (synthsyms);
> We can only safely do this, but .name is leaked for x86_64.  Other
> tools using bfd, like objdump, nm, and gprof may have this issue too.
> I'll ask binutils people on asymbol allocation and de-allocation.
>