PR28055, segfault in bpf special reloc function

[Jose E. Marchesi]

Hi Alan.

> The testcase in this PR tickled two bugs fixed here.  output_bfd is
> NULL when a reloc special_function is called for final linking and
> when called from bfd_generic_get_relocated_section_contents.  Clearly
> using output_bfd is wrong as it results in segfaults.  Not only that,
> the endianness of the reloc field really should be that of the input.
> The second bug was not checking that the entire reloc field was
> contained in the section contents.

Thanks for fixing this.

> I was going to add the following too, but it looks like this would
> only be dead code since ld -r isn't supported in combination of input
> and output that would see this special_function called.
>
>   /* If this is a relocatable link (output_bfd test tells us), just
>      call the generic function.  */
>   if (abfd != output_bfd && output_bfd != NULL)
>     return bfd_elf_generic_reloc (abfd, reloc_entry, symbol, data,
> 				  input_section, output_bfd, error_message);
>
>
> 	PR 28055
> 	* elf64-bpf.c (bpf_elf_generic_reloc): Use correct bfd for bfd_put
> 	and bfd_put_32 calls.  Correct section limit checks.
>
> diff --git a/bfd/elf64-bpf.c b/bfd/elf64-bpf.c
> index 28c1543c0b6..243df93ae82 100644
> --- a/bfd/elf64-bpf.c
> +++ b/bfd/elf64-bpf.c
> @@ -589,14 +589,15 @@ elf64_bpf_merge_private_bfd_data (bfd *ibfd, struct bfd_link_info *info)
>  }
>  
>  /* A generic howto special function for installing BPF relocations.
> -   This function will be called by the assembler (via bfd_install_relocation).
> +   This function will be called by the assembler (via bfd_install_relocation),
> +   and by various get_relocated_section_contents functions.
>     At link time, bpf_elf_relocate_section will resolve the final relocations.
>  
>     BPF instructions are always big endian, and this approach avoids problems in
>     bfd_install_relocation.  */
>  
>  static bfd_reloc_status_type
> -bpf_elf_generic_reloc (bfd * abfd, arelent *reloc_entry, asymbol *symbol,
> +bpf_elf_generic_reloc (bfd *abfd, arelent *reloc_entry, asymbol *symbol,
>  		       void *data, asection *input_section,
>  		       bfd *output_bfd,
>  		       char **error_message ATTRIBUTE_UNUSED)
> @@ -607,7 +608,15 @@ bpf_elf_generic_reloc (bfd * abfd, arelent *reloc_entry, asymbol *symbol,
>    bfd_byte *where;
>  
>    /* Sanity check that the address is in range.  */
> -  if (reloc_entry->address > bfd_get_section_limit (abfd, input_section))
> +  if (reloc_entry->howto->type == R_BPF_INSN_64)
> +    {
> +      bfd_size_type end = bfd_get_section_limit_octets (abfd, input_section);
> +      if (reloc_entry->address > end
> +	  || end - reloc_entry->address < 16)
> +	return bfd_reloc_outofrange;
> +    }
> +  else if (!bfd_reloc_offset_in_range (reloc_entry->howto, abfd, input_section,
> +				       reloc_entry->address))
>      return bfd_reloc_outofrange;
>  
>    /*  Get the symbol value.  */
> @@ -640,15 +649,15 @@ bpf_elf_generic_reloc (bfd * abfd, arelent *reloc_entry, asymbol *symbol,
>  	 instructions, and the upper 32 bits placed at the very end of the
>  	 instruction. that is, there are 32 unused bits between them. */
>  
> -      bfd_put_32 (output_bfd, (relocation & 0xFFFFFFFF), where + 4);
> -      bfd_put_32 (output_bfd, (relocation >> 32), where + 12);
> +      bfd_put_32 (abfd, (relocation & 0xFFFFFFFF), where + 4);
> +      bfd_put_32 (abfd, (relocation >> 32), where + 12);
>      }
>    else
>      {
>        /* For other kinds of relocations, the relocated value simply goes
>  	 BITPOS bits from the start of the entry. This is always a multiple
>  	 of 8, i.e. whole bytes.  */
> -      bfd_put (reloc_entry->howto->bitsize, output_bfd, relocation,
> +      bfd_put (reloc_entry->howto->bitsize, abfd, relocation,
>  	       where + reloc_entry->howto->bitpos / 8);
>      }