From: "Carlos O'Donell" <carlos@redhat.com>
To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: libc-alpha <libc-alpha@sourceware.org>,
"libc-ports@sourceware.org" <libc-ports@sourceware.org>
Subject: Re: [PATCH 2/5] __FD_ELT: Implement correct buffer overflow check
Date: Fri, 03 May 2013 03:15:00 -0000 [thread overview]
Message-ID: <51832BE1.8020303@redhat.com> (raw)
In-Reply-To: <518176FC.5030906@gmail.com>
On 05/01/2013 04:11 PM, KOSAKI Motohiro wrote:
>>> Does compiling ruby (or similar code) with this header
>>> result in calls to __fdelt_buffer_warn or __fdelt_buffer_chk?
>>
>> Unfortunately, No. __builtin_object_size() require compiler know the
>> buffer size.
>> In the other words, it doesn't work if an allocate function and
>> FD_{SET,CLR} functions
>> doesn't exist in the same place. This is the same limitation with
>> other string buffer
>> overflow checks.
>
> I inspected several other project codes.
Thank you very much for looking at these examples. They are quite
informative.
[snip]
> Summary: alomost software only need to add alloc_size() annotation to xmalloc() or
> similar in almost case. but there are several exceptions. some software have a complicated
> fd size management and can't use __builtin_object_size(). but that's ok. In this case, the
> software correctly expand buffers by realloc() or similar, so there is no chance to happen
> buffer overflow.
So with your patch we enhance the number of cases that the check
is correct by using __bos0, and that's forward progress. I know
that it is less progress than you would like, but it is good
progress.
We keep _FORTIFY_SOURCE working usefully, even though it still
yields false positives.
The question as always with these checks is: Do you prefer false
positives or buffer overflows?
What's more harmful? The ecosystem thinking glibc and
the tools are "wrong" or buffer overflows leading to
security issues?
As a conservative project, and given the goal of _FORTIFY_SOURCE,
it seems like we have to leave the existing checks in place.
Cheers,
Carlos.
next prev parent reply other threads:[~2013-05-03 3:15 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-14 0:47 [PATCH v4 0/5] fix wrong program abort on __FD_ELT KOSAKI Motohiro
2013-04-14 0:47 ` [PATCH 2/5] __FD_ELT: Implement correct buffer overflow check KOSAKI Motohiro
2013-05-01 2:42 ` Carlos O'Donell
2013-05-01 6:28 ` KOSAKI Motohiro
2013-05-01 14:42 ` Carlos O'Donell
2013-05-01 20:32 ` KOSAKI Motohiro
2013-05-03 3:15 ` Carlos O'Donell
2013-05-01 20:11 ` KOSAKI Motohiro
2013-05-03 3:15 ` Carlos O'Donell [this message]
2013-04-14 0:47 ` [PATCH 3/5] update libc.abilist KOSAKI Motohiro
2013-04-14 0:47 ` [PATCH 5/5] __FDS_BITS: Added cast to __fd_mask* to avoid warning KOSAKI Motohiro
2013-05-01 2:44 ` Carlos O'Donell
2013-04-14 0:47 ` [PATCH 4/5] tst-chk1: add fd_set dynamic allocation test KOSAKI Motohiro
2013-05-01 2:44 ` Carlos O'Donell
2013-05-01 6:29 ` KOSAKI Motohiro
2013-04-14 0:47 ` [PATCH 1/5] __fdelt_chk: Removed range check KOSAKI Motohiro
2013-05-01 2:25 ` Carlos O'Donell
2013-05-01 6:40 ` KOSAKI Motohiro
2013-05-01 14:45 ` Carlos O'Donell
2013-05-01 22:13 ` KOSAKI Motohiro
2013-05-03 2:52 ` Carlos O'Donell
2013-05-01 3:08 ` [PATCH v4 0/5] fix wrong program abort on __FD_ELT Carlos O'Donell
2013-05-01 5:31 ` KOSAKI Motohiro
2013-05-01 14:38 ` Carlos O'Donell
2013-05-01 22:21 ` KOSAKI Motohiro
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