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Hi, first off, sorry if my write-up seemed a bit harsh, this was the
last time I am trying to respond to a change proposal late at
night :). On 12/6/22 14:14, Siddhesh Poyarekar
wrote:
This is interesting to know. I was not aware of this as I do not follow other distributions closely.On Mon, Dec 5, 2022 at 7:35 PM Jaroslav Prokop <jar.prokop@xxxxxxxx> wrote:Default C and C++ compiler flags to build packages in Fedora currently includes `-Wp,-D_FORTIFY_SOURCE=2`, which enables fortification of some functions in glibc, thus providing some mitigation against buffer overflows. Since glibc 2.34 and GCC 12, there has been a new fortification level (`_FORTIFY_SOURCE=3`) which improves the coverage of this mitigation. The core change to bring in this mitigation is to change the default build flags in `redhat-rpm-config` so that packages build by default with `-Wp,-D_FORTIFY_SOURCE=3`. There are packages (e.g. `systemd`) that do not interact well with `_FORTIFY_SOURCE` and will also need a workaround to downgrade fortification to level 2. The change will also include this override. How come systemd gets an exception? If it is a security option, it should be enabled everywhere.It's an unfortunate (although hopefully temporary) exclusion, see this issue for more context: https://github.com/systemd/systemd/issues/22801 In summary, systemd uses malloc_usable_size in a way that it's discouraged, which results in behaviour that's undefined by the standard, which is now caught out by the compiler. We're hoping to convince the systemd community to fix this so that we can actually build it with fortification.I do not see benefit in a security change that ignores PID 1 process,Do you mean that factually or rhetorically? I've shared statistics of improvement in the proposal, surely improvements to packages like bash, sudo and coreutils would count for something :)If the feature, on the GCC side, is not 100% done. How do I tell a difference of a bug with the _FORTIFY_SOURCE which I will ignore and a bug with my package?_FORTIFY_SOURCE=3 has been enabled on OpenSUSE for nearly a year. If it causes a crash in your package, it's extremely likely that your package has a bug. I would have appreciated seeing this noted on the proposal. I then know I can compare spec files / build results with the relevant counterparts if it works for them but not for us. To this point, including and opt-out mechanism is IMO reasonable.I do not have the knowledge or the time to be able to say that GCC generated the wrong machine code and therefore it is not a bug with my package. If my program was not complaining before the change and is now complaining with the change, I am opting out of the change, and filing a bug against GCC on Fedora. I assume that by the package providing the exception, packagers get to choose themselves and we do not need to go through FESCO to disable a security feature?I think they should have to, but that's something for FESCO to decide. _FORTIFY_SOURCE is not a new feature, the new level is just better at catching bugs. Significantly better. Even including a "reference" to the opt out mechanism of the current _FORTIFY_SOURCE level, should it be the same, is valuable. Ah, I was starting to get mixed up the sheet pages. The "Raw data - All x86_64" include the sentence "Note: Summary data since Google sheets didn't like the raw data".== Benefit to Fedora == [https://docs.google.com/spreadsheets/d/1nPSmbEf3HVB91zI8yBraMqVry3_ILmlV2Z5K7FZeHZg/edit?usp=sharing Analysis of packages] in Fedora rawhide indicate that the improvement of mitigation coverage is on average over 2.4x, in some cases protecting more than half of the fortified glibc calls in the target application. This change will thus harden Fedora to a significant extent, thus making it a more secure distribution out of the box. 1) Is there some complete source for all these findings? If google sheets cannot handle all the "raw data" as noted in the comment, maybe it is the wrong medium.I've literally posted the raw data in the sheets, please take a look. Other raw data variants seem to be correctly "raw". What I was trying to say with that paragraph is that the format is hard to understand for me and I really did not expect2) What does *anything* on that google sheet mean. I have managed to figure out, from the article, that bos and bdos correspond to level 2 and 3 of _FORTIFY_SOURCE. However, total of /.*/? Violated accesses? Segfaults? Then followed by "Sum of total". For rubygem-ffi, this reaches into hundreds while "bdos" is 2. That is the only sum I can make, with the data provided. I am no wiser from looking at it, what do the data mean?I've mentioned this in the article, but it's a compile-time statistic of the number of success of __builtin_object_size vs __builtin_dynamic_object_size, using the fortify-metrics plugin: https://github.com/siddhesh/fortify-metrics The numbers you should be looking at are the "coverage" columns, which tells you what percentage of the calls were successful. For rubygem-ffi, the fortification is negligible regardless of whether it is built at _FORTIFY_SOURCE=2 or _FORTIFY_SOURCE=3. This means that it is unaffected by this change. the description or link to it under "More trapped buffer overflows". A line next to the link in the Fedora Change along the lines of
"Collected via fortify-metrics, see <fortify-metrics repo>." I'll be honest, I do not expect that much of an improvement if the package using only Ruby provided memory C-API (which is why you probably searched only for glibc-devel).3) I cannot speak to much else than Ruby, I do not see ruby in neither the failures or "All x86_64". Should we attempt to test it ourselves?That's odd, thanks for pointing out.Please provide a proper "how to test" section, I cannot fix what I cannot test or compare results when I have no idea what I am seeing. Actually, last time I heard about number of packages, it was around 50k (not source, build result), and as I stated, Ruby is missing, and so are quite a few dependent packages that should have GCC involved somewhere: ~~~ $ dnf repoquery --whatrequires "*libruby.so*" --disablerepo="*" --enablerepo="fedora" 2>/dev/null | grep -v "i686" | uniq | wc -l 115 ~~~ If we also filter rubygem-* packages that depend on the *libruby.so* (and most probably contain a binary extension written in C/C++ that links to Ruby), I get 68 packages. When I search "All x86_64" for "ruby" I get 28 packages. That is... not adding up.Yeah, I have missed packages; I had looked at revdeps glibc-devel, which turned out around 9k packages, of which 6k had any _FORTIFY_SOURCE use at all. I can redo with *all* packages and generate a report. Thank you and Florian for speaking up to this point. Again, I would appreciate if this would be noted in the change proposal== Scope == * Proposal owners: Post a merge request to redhat-rpm-config with the actual change to build flags. * Other developers: Resolve bugs filed for build failures, either by fixing the bug exposed by `_FORTIFY_SOURCE=3` or by disabling `_FORTIFY_SOURCE=3` for the package if it is a false positive or if the package is unable to adapt to the change. * Release engineering: Mass rebuild required * Policies and guidelines: Guidelines should include workaround for packages that fail to build with `-Wp,-D_FORTIFY_SOURCE=3` due to a false positive. I'll just ask, what is a false positive. How can I tell. What are the steps for this.If _FORTIFY_SOURCE causes crashes in your package, it's most likely a bug in your package. In the rare case of a false positive (or even if in doubt or if you can't figure out what the bug is), cc me and I'll help you determine what to do there. as that will be the document I consult first if I suspect that _FORTIFY_SOURCE might be causing problems. What I had in mind here are use cases like Ruby C extensions.* Trademark approval: N/A (not needed for this Change) == Upgrade/compatibility impact == No ABI change, so there should be no impact on compatibility in a mixed environment. == How To Test == * Smoke testing of packages to ensure that they continue to work correctly. Some packages may have overflows exposed at runtime, which may need to be fixed. This does not describe how to test, e.g. ahead of time, just that the packagers are to deal with the fallout...cc me, I'll be happy to help you out. If Ruby's GC goes anywhere close to the related calls and there is a bug in the API, we cannot validate it without first rebuilding Ruby and then all the related binary extensions with the option to cover most ground. Maybe I am chasing a red herring with this, but I generally err
on the side of caution. Thank you, I'd appreciate that.I did a rebuild of nearly 10k packages and there were few failures (see the failures tab in the doc). I'll expand that list to make sure that the pain on maintainers is minimal. I agree that this one seems more open to interpretation what belongs where.== User Experience == No noticeable change to users. I beg to differ. From what I am able to tell, from the limited provided sources, packages can have a runtime crash. A LOT of GUI packages use C or the likes that respond to the flags of "fortify source". This can have a serious impact to users by the recompiled packages: * not suddenly working, package's tests passed, but user triggered just the right code branch * performance impacted due to overhead.I don't think that's the intended definition of "User Experience" here, but I'll be happy to add to it if needed. What I latch on to is the following sentence in the change template "Describe what Users will see or notice, for example:" As a user I will definitely notice app crashing :) . I am not as worried about this since I found out, via the
discussion, that other distributions have this as a default for
some time now. Thanks for the response,Thanks, Sid Jarek |
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