Re: Synthetic symbol leak in in elf_x86_64_get_synthetic_symtab and elf_read_minimal_symbols

Yao Qi
2017-08-11T09:27:17Z

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.

--
Yao (é½å°§)