[gentoo-dev] Portage to die on sure-enough _FORTIFY_SOURCE overflows

["Diego Elio Pettenò" <flameeyes@gmail.com>]

Hi all,

since the last time I asked Zac about this it came back to bite me[1]
this time I'm going to send the announce to the list first, and if
nobody can actually come up with a good reason not to, I'm going to ask
Zac tomorrow to re-enable the feature.

What is this about? Portage already reports some of the overflow
warnings coming from the glibc fortified sources (-D_FORTIFY_SOURCE=2
-O2 — enabled since gcc 4.3.3-r1 and even stronger with gcc 4.5 and
glibc 2.12+, afaict), but they really are divided into two categories:

- might overflow (depends on combination of parameters and variables the
compiler can't completely untangle);
- _will_ overflow (whenever that code path is hit, an overflow will
happen).

The former we should highlight but not die upon; the latter, though...

As Mike and me expressed on the linked bug, code that is built with that
warning is code that is going to crash as surely as

char *foo = NULL;
foo[3] = 'a';

which could result in nasty surprises for users (see [2] for the whole
reasoning).

Now, we've not seen "proper" false positives (in the Portage sense I
mean — because even if the C library hits a false positive, it _will_
crash with an abort() from its own code!), but Kumba pointed me at a
case that wasn't entirely clear, and took a bit of detective work to
track down [3] so you could have users report issues you cannot easily
identify or reproduce. I cannot make promises, but if all else fail I'll
see to be around to help you with those cases.

So if you want to have your say, gentoo-qa is there for that.

Thank you,

[1] https://bugs.gentoo.org/show_bug.cgi?id=337031
[2]
http://blog.flameeyes.eu/2010/09/14/not-all-failures-are-caused-equal
[3]
http://blog.flameeyes.eu/2010/09/12/some-_fortify_source-far-fetched-warnings-are-funny

-- 
Diego Elio Pettenò — “Flameeyes”
http://blog.flameeyes.eu/

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