Re: [committed, PATCH] Check file size before getting section contents

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Jun 26, 2017 at 3:24 PM, Pedro Alves <palves@redhat.com> wrote:
> On 06/26/2017 10:48 PM, Pedro Alves wrote:
>> Hi H.J.,
>>
>> This patch caused many regressions in GDB's testsuite:
>>
>>   https://sourceware.org/ml/gdb-testers/2017-q2/msg05045.html
>>
>> x86 buildslaves haven't caught up with the patch yet, but I
>> see the same thing locally, on my x86-64 machine.  (git bisect
>> pointed me here.)
>>
>> Here's quick way to run only a few of the tests that are now failing:
>>
>>  $ make check TESTS="gdb.base/break-interp.exp gdb.base/corefile.exp gdb.base/solib-search.exp gdb.reverse/sigall-precsave.exp"
>>
>> Any idea what's going on?
>>
>> BTW, this looks very suspicious:
>>
>>  @@ -867,7 +876,13 @@ _bfd_generic_get_section_contents_in_window
>>       sz = section->rawsize;
>>     else
>>       sz = section->size;
>>  +  filesz = bfd_get_file_size (abfd);
>>  +    {
>>  +      /* This should never happen.  */
>>  +      abort ();
>>  +    }
>>
>> ... because that abort is unconditional.  Did you intend
>> to guard it with:
>>    if (filesz < 0)
>> like in _bfd_generic_get_section_contents?
>>
>
>> @@ -811,8 +812,15 @@ _bfd_generic_get_section_contents (bfd *abfd,
>>      sz = section->rawsize;
>>    else
>>      sz = section->size;
>> +  filesz = bfd_get_file_size (abfd);
>> +  if (filesz < 0)
>> +    {
>> +      /* This should never happen.  */
>> +      abort ();
>> +    }
>>    if (offset + count < count
>> -      || offset + count > sz)
>> +      || offset + count > sz
>> +      || (section->filepos + offset + sz) > (bfd_size_type) filesz)
>>      {
>
> The problem is this new "section->filepos + offset + sz"
> check here.  GDB calls bfd_get_section_contents with offset != 0,
> which causes that "offset + sz" addition to shoot past filesz.
> I can't see how that new check makes sense as is.  We're reading
> "count" bytes, not "sz" bytes.

Please try this:

diff --git a/bfd/libbfd.c b/bfd/libbfd.c
index 7b270ef..8bad4ab 100644
--- a/bfd/libbfd.c
+++ b/bfd/libbfd.c
@@ -820,7 +820,7 @@ _bfd_generic_get_section_contents (bfd *abfd,
     }
   if (offset + count < count
       || offset + count > sz
-      || (section->filepos + offset + sz) > (bfd_size_type) filesz)
+      || (section->filepos + sz) > (bfd_size_type) filesz)
     {
       bfd_set_error (bfd_error_invalid_operation);
       return FALSE;
@@ -883,7 +883,7 @@ _bfd_generic_get_section_contents_in_window
       abort ();
     }
   if (offset + count > sz
-      || (section->filepos + offset + sz) > (bfd_size_type) filesz
+      || (section->filepos + sz) > (bfd_size_type) filesz
       || ! bfd_get_file_window (abfd, section->filepos + offset, count, w,
  TRUE))
     return FALSE;

> I'm testing this.
>
> From: Pedro Alves <palves@redhat.com>
> Date: 2017-06-26 22:51:02 +0100
>
> Fix
> ---
>
>  bfd/libbfd.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/bfd/libbfd.c b/bfd/libbfd.c
> index b903328..b8c65b5 100644
> --- a/bfd/libbfd.c
> +++ b/bfd/libbfd.c
> @@ -820,7 +820,7 @@ _bfd_generic_get_section_contents (bfd *abfd,
>      }
>    if (offset + count < count
>        || offset + count > sz
> -      || (section->filepos + offset + sz) > (bfd_size_type) filesz)
> +      || (section->filepos + offset + count) > (bfd_size_type) filesz)
>      {
>        bfd_set_error (bfd_error_invalid_operation);
>        return FALSE;
> @@ -877,6 +877,7 @@ _bfd_generic_get_section_contents_in_window
>    else
>      sz = section->size;
>    filesz = bfd_get_file_size (abfd);
> +  if (filesz < 0)
>      {
>        /* This should never happen.  */
>        abort ();
>



-- 
H.J.