elf: Check corrupt VTENTRY relocation addend

[Alan Modra]

On Tue, Sep 23, 2025 at 04:42:51PM +0200, Jan Beulich wrote:
> On 23.09.2025 13:57, Alan Modra wrote:
> > On Tue, Sep 23, 2025 at 10:16:50AM +0800, H.J. Lu wrote:
> >> --- a/bfd/elflink.c
> >> +++ b/bfd/elflink.c
> >> @@ -14895,6 +14895,15 @@ bfd_elf_gc_record_vtentry (bfd *abfd, asection *sec,
> >>  	}
> >>        size = (size + file_align - 1) & -file_align;
> >>  
> >> +      if (addend > size)
> > 
> > For this to happen you must have had an overflow in prior expressions
> > calculating size from addend, I think.  Perhaps it might be better to
> > limit vtentry reloc addends to something a lot smaller than -8ul
> > (which I think is effectively what your patch does), to prevent insane
> > vtable memory allocation.  What is a reasonable limit to c++ vtable
> > size?
> 
> Can we really build in a heuristic like that? Arbitrarily complex class
> hierarchies can have arbitrarily large vtables, I suppose.

We can in this case.  I doubt anyone would notice if gas
.vtable_inherit and .vtable_entry disappeared along with all the
support for VTINHERIT and VTENTRY relocs.  See gcc commit a0c8285b03a4.
I am committing the following patch.


PR 33452 SEGV in bfd_elf_gc_record_vtentry

Limit addends on vtentry relocs, otherwise ld might attempt to
allocate a stupidly large array.  This also fixes the expression
overflow leading to pr33452.  A vtable of 33M entries on a 64-bit
host is surely large enough, especially considering that VTINHERIT
and VTENTRY relocations are to support -fvtable-gc that disappeared
from gcc over 20 years ago.

	PR ld/33452
	* elflink.c (bfd_elf_gc_record_vtentry): Sanity check addend.

diff --git a/bfd/elflink.c b/bfd/elflink.c
index 54f0d6e957e..0a0456177c2 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -14865,7 +14865,7 @@ bfd_elf_gc_record_vtentry (bfd *abfd, asection *sec,
   const struct elf_backend_data *bed = get_elf_backend_data (abfd);
   unsigned int log_file_align = bed->s->log_file_align;
 
-  if (!h)
+  if (!h || addend > 1u << 28)
     {
       /* xgettext:c-format */
       _bfd_error_handler (_("%pB: section '%pA': corrupt VTENTRY entry"),


-- 
Alan Modra