Windows 95 defenses against installers that overwrite a file with an older one

https://devblogs.microsoft.com/oldnewthing/20260324-00/?p=112159

by michelangelo • 4 months ago

168 100 4 months ago

devblogs.microsoft.com

forkerenok• 4 months ago

OMG, is this the reason why every other installer would get stuck at 99% forever? :D

It doesn't say for certain, but assuming the version of this they settled on (restoring components after the installation finished) is what they shipped in the original version of Windows 95, then no, I don't think this could have caused hangs in the installer itself (unless Win95 misjudged whether the installer had completed or not and started the restore process early?).

elzbardico2• 4 months ago

No, most likely bad algorithms for dealing with registry stuff. The kind of thing that worked well on tester machines with small registry sizes and exploded in the real world.

ElectricalUnion• 4 months ago

Someone thought the "commit all previous operations to persistent storage" step would take just 1% of the time.

akdev1l4• 4 months ago

Windows 95 worked around this by keeping a backup copy of commonly-overwritten files in a hidden C:\Windows\SYSBCKUP directory. Whenever an installer finished, Windows went and checked whether any of these commonly-overwritten files had indeed been overwritten.

This is truly unhinged. I wonder if running an installer under wine in win95 mode will do this.

calgarymicro2• 4 months ago

If . . . the replacement has a higher version number than the one in the SYSBCKUP directory, then the replacement was copied into the SYSBCKUP directory for safekeeping.

This as well. I know there are a million ways for a malicious installer to brick Win95, but a particularly funny one is hijacking the OS to perpetually rewrite its own system components back to compromised version number ∞ whenever another installer tries to clean things up.

bombcar• 4 months ago

This is truly unhinged.

This is bog-standard boring stuff (when presented with a similar problem, Linux invented containers lol) - read some of his other posts to realize the extent Microsoft went to maintain backwards compatibility - some are insane, some no doubt led to security issues, but you have to respect the drive.

akdev1l4• 4 months ago

It’s not bog-standard. Containers are not equivalent to doing what is described in the article.

Containers are in fact redirecting writes so an installer script could not replace system libraries.

The equivalent would be a Linux distro having the assumption that installer scripts will overwrite /usr/lib/libopenssl.so.1 with its own version and just keeping a backup somewhere and copying it back after the script executes.

No OS that I know of does that because it’s unhinged and well on Linux it would probably break the system due to ABI compatibility.

If they had taken essentially the same approach as wine and functionally created a WINEPREFIX per application then it would not be unhinged.

edit: also to be clear, I respect their commitment to backwards compatibility which is what leads to these unhinged decisions. I thoroughly enjoy Raymond Chen’s dev blog because of how unhinged early windows was.

rkagerer• 4 months ago

This is truly unhinged

Granted, but at the same time it's also resolutely pragmatic.

Apparently there was already lots of software out there which expected to be able to write new versions of system components. As well as buggy software that incidentally expected to be able to write old versions, because its developers ignored Microsoft's published best practices (not to mention common sense) and and didn't bother to do a version comparison first.

The choice was to break the old software, or let it think it succeeded then clean up after the mess it made. I'd bet they considered other alternatives (e.g. sandbox each piece of software with its own set of system libraries, or intercept and override DLL calls thus ignoring written files altogether) but those introduce more complexity and redirection with arguably little benefit. (I do wonder if the cleanup still happens if something like an unexpected reboot or power loss happens at exactly the wrong time).

Could the OS have been architected in a more robust fashion from the get-go? Of course.

Could they have simply forbidden software from downgrading system components? Sure, but it'd break installers and degrade the user experience.

Since the OS historically tolerated the broken behavior, they were kind of stuck continuing to tolerate it. One thing I learned leading groups of people is if you make a rule but don't enforce it, then it isn't much of a rule (at least not one you can rely on).

I would argue the deeper mistake was not providing more suitable tooling for developers to ensure the presence of compatible versions of shared libraries. This requires a bit of game theory up front; you want to always make the incorrect path frictiony and the correct one seamless.

badsectoracula4• 4 months ago

There was (and still is) VerInstallFile, however this was introduced in Windows 3.1 and it is possible installers wanted to also support Windows 3.0 (since there wasn't much of a time gap between the two many programs tried to support both) so they didn't use it.

xenadu02• 4 months ago

It is important to remember that Microsoft created some of this chaos to begin with. Other aspects can be attributed to "the industry didn't understand the value of $x or the right way to do $y at the time". And some of this is "nonsense you deal with when the internet and automatic updates is not yet a thing".

Why did programs overwrite system components? Because Microsoft regularly pushed updates with VC++ or Visual Studio and if you built your program with Microsoft's tools you often had to distribute the updated components for your program to work - especially the Visual C runtime and the Common Controls. This even started in the Win3.11 days when you had to update common controls to get the fancy new "3d" look. And sometimes a newer update broke older programs so installers would try to force the "correct" version to be installed... but there's no better option here. Don't do that and the program the user just installed is busted. Do it and you break something else. There was no auto-update or internet access so you had to make a guess at what the best option was and hope. Mix in general lack of knowledge, no forums or Stack Overflow to ask for help, and general incompetence and you end up with a lot of badly made installers doing absolute nonsense.

Why force everyone to share everything? Early on primarily for disk space and memory reasons. Early PCs could barely run a GUI so few hundred kilobytes to let programs have their own copy of common controls was a non-starter. There was no such thing as "just wait for everyone to upgrade" or "wait for WindowsUpdate to roll this feature out to everyone". By the early 2000s the biggest reason was because we hadn't realized that sharing is great in theory but often terrible in practice and a system to manage who gets what version of each library is critical. And we also later had the disk space and RAM to allow it.

But the biggest issue was probably Microsoft's refusal to provide a system installer. Later I assume antitrust concerns prevented them from doing more in this area. Installers did whatever because there were a bunch of little companies making installers and every developer just picked one and built all their packages with it. Often not updating their installer for years (possibly because it cost a lot of money).

Note: When I say "we" here that's doing a lot of heavy lifting. I think the Unix world understood the need for package managers and control of library versions earlier but even then the list of problems and the solutions to them in these areas varied a lot. Dependency management was far from a solved problem.

canucker2016• 4 months ago

You'd have to track down some 16bit Win3.x software to install. Probably on floppy disks since CD-ROMs weren't common.

jasonfarnon2• 4 months ago

Whats unhinged about a periodic integrity check? Doesn't seem much different than a startup/boot check. If you're talking about security, you've come to the wrong OS.

justsomehnguy3• 4 months ago

Then blindly overwriting the shared libraries despite the guidance what the vendor of the OS provides is actually hinged, yes?

LocalH• 4 months ago

I agree, it's unhinged for applications to overwrite newer versions of system files with older ones.

Lammy2• 4 months ago

Whenever an installer finished, Windows went and checked whether any of these commonly-overwritten files had indeed been overwritten.
Basically, Windows 95 waited for each installer to finish

How could it tell that a particular process was an installer? Just anything that writes to the PROGRA~1 or WINDOWS folders?

layer83• 4 months ago

The latter, according to https://devblogs.microsoft.com/oldnewthing/20260324-00/?p=11...

Lammy2• 4 months ago

Egg on my face for not scrolling down to see the comments after reading the article. Thanks!

chihuahua2• 4 months ago

It must have been difficult and frustrating to work as part of the Windows team back in those days.

You see all the wacky software that doesn't follow the rules properly, does whatever it wants, breaks things. And you have to figure out how Windows can accommodate all that software, keep it from breaking, and also prevent it from messing up a computer or undo the damage.

They did not have the option of saying "this app developer wrote shitty software, sucks to be them, not my problem."

I wonder how much of this problem was caused by lack of adequate documentation describing how an installer should behave, and how much was developers not reading that documentation and being content when it works on their machine.

layer83• 4 months ago

I wonder how much of this problem was caused by lack of adequate documentation describing how an installer should behave, and how much was developers not reading that documentation and being content when it works on their machine.

It was mostly the latter. And when Windows broke, people would blame it on Microsoft, not on the software they installed. The same if the software broke. And you didn’t have online updates at the time that could retroactively add fixes. So Microsoft had to do everything they could to ensure broken software would still work, while also keeping Windows working, the best they could.

kstrauser• 4 months ago

So Microsoft had to do everything they could to ensure broken software would still work

I think they chose to do everything they could to keep it limping along. An alternative would've been a name-and-shame approach, like "This program crashed because the author made this mistake: [short description or code or whatever]", and leave them out to try until the devs stopped doing those dumb things. After a few years of pain, people would've gotten with the program, so to speak. Instead, they chose the path that put zero pressure on devs to write correctly-behaving software.

bigstrat2003• 4 months ago

One of the craziest Raymond Chen stories is one where a Windows API call would return a pointer to a data structure the OS had allocated for the operation. The programmers at Microsoft made the data structure bigger than they needed, for future expansion. But some third party devs noticed the extra space, and started to use it to store data for their program. Then when Windows tried to start using the extra space, those applications would crash.

Reasonable people can disagree on a lot of things in programming. But I still do not understand how one can consider writing to memory the OS owns to be ok. It's sheer professional malpractice to do that kind of thing. With stuff like that, I don't think that any amount of documentation would have helped. The issue was that those programmers simply did not care about anything except getting their own program working, and did whatever the most expedient method was to get there.

jjmarr• 4 months ago

But I still do not understand how one can consider writing to memory the OS owns to be ok.

Your manager tells you to reduce memory usage of the program "or else".

Legend2440• 4 months ago

I still do not understand how one can consider writing to memory the OS owns to be ok.

Things were different back then. People did a lot of hacky stuff to fit their programs into memory, because you were genuinely constrained by hardware limitations.

Not to mention, the idea of the OS owning the machine was not as well developed as it is today. Windows 3.11 was just another program, it didn't have special permissions like modern OSes, and you would routinely bypass it to talk to the hardware directly.

acuozzo2• 4 months ago

But I still do not understand how one can consider writing to memory the OS owns to be ok.

Go to Vogons and look at all of the memory tricks people will use to get various games running on MS-DOS. This kind of juggling exactly which drivers to load, etc. is why Microsoft added the boot menu in MS-DOS 6.0 to CONFIG.SYS.

I'm not necessarily saying that this was the case here, but it smells like that to me.

gzread3• 4 months ago

Ask the Zig people, who just started relying on undocumented unstable Windows behaviour intentionally due to some kind of religious belief: https://codeberg.org/ziglang/zig/issues/31131

Hackbraten2• 4 months ago

Back then, many programmers originally learned their ropes in an 8-bit home computer era (or earlier), where it used to be completely normal and even necessary that you used whatever memory region you got away with.

For example, on the C64, you would get away with using the memory locations $02, $2A, $52, $FB to $FE, $02A7 to $02FF, and $0313 as scratch space for your own programs. Memory was incredibly scarce. I can’t blame programmers for sticking with their habits and for taking several years to unlearn and adjust their misconceptions about who owns what if they came from a home computer era where that pattern used to be the only way to get stuff done.

topspin4• 4 months ago

One workaround Microsoft has done for use-after-free is detecting when an application is prone to this and using an allocator that doesn't actually free RAM immediately. It believe that lovely bit of fun is a function of "Heap Quarantine".

Yes, the real, can't say no world of system software is not what one might wish.

Krutonium• 4 months ago

IIRC Sim City 2000 is one such piece of software.

anthk• 4 months ago

Not too different to using MS's mimalloc to run zenlisp under OpenBSD because the core malloc will just tell good try, but GTFO to the interpreter.

MarkSweep3• 4 months ago

I wonder how much of this problem was caused by lack of adequate documentation describing how an installer should behave, and how much was developers not reading that documentation and being content when it works on their machine.

There is a third option: the developers knew the rules and chose to ignore them for some reason. A modern example of this is the Zig language’s decision to reverse engineer and use undocumented APIs in Windows in preference of using documented APIs.

https://codeberg.org/ziglang/zig/issues/31131

iknowstuff• 4 months ago

Kinda wild

throwA29B• 4 months ago

ignore them for some reason

The reasons are clearly stated in the issue you have linked.

gzread3• 4 months ago

Wow! What a mind-bogglingly stupid idea. I will cancel my plans to learn Zig.

kaashif• 4 months ago

This comment is pretty wild:

In addition to what @The-King-of-Toasters said, the worst case scenario is really mild: A new version of windows comes out, breaking ntdll compatibility. Zig project adds a fix to the std lib. Application developer recompiles their zig project from source, and ships an update to their users.

Uh so what if the application developer isn't around any more?

The fact that they consider the worst case to be one where the application is still actively supported and the developer is willing to put up with this nonsense is pretty surprising. Not sure how anyone could believe that.

RiverCrochet2• 4 months ago

Before Windows 95/3.x, there was DOS.

There were no rules in DOS, or r_x permissions like Unix.

The DOS kernel itself didn't really impose any structure on the filesystem. All that mattered was:

- The two files that comprised DOS itself (MSDOS.SYS, IO.SYS) had to be "inode" 0 and 1 on the disk in early versions,

- the kernel parsed \CONFIG.SYS on boot, and I think looked for \COMMAND.COM if you didn't specify a different shell with COMSPEC= in CONFIG.SYS. There were defaults if \CONFIG.SYS didn't exist, but of course all your DEVICE= stuff won't load and you'll probably not have a working mouse, CD-ROM, etc.

\AUTOEXEC.BAT was optional. That's it. Any other files could be anywhere else. I think the MS-DOS installer disk put files in C:\DOS by convention but that was just a convention. As long as COMMAND.COM was findable DOS would boot and be useable-and if you mucked something up you just grab your DOS boot floppy with A:\COMMAND.COM on it and fix it.

From what I recall most installers-if provided-made a directory in \ and put all their files there, mixing executables with read-write data. There was no central registry of programs or anything unless you were using a third party front-end.

Windows 3.x and 95 inherited the DOS legacy there.

mrighele• 4 months ago

I think the MS-DOS installer disk put files in C:\DOS by convention but that was just a convention.

That assume that you where going to install the OS, which assumes that you had an hard drive :-). The original IBM PC didn't, and anyway MS-DOS didn't support folders until version 2.0.

On those old PCs you would boot your computer on a floppy drive with all the files on the root of a floppy, and execute your command there. There was not much to work with anyway, check the content of the boot floppy of MSDOS 1.0 [1].

And also, especially if you had a single floppy, you wouldn't even use it: to run your software you would boot a disk with a IO.SYS, MSDOS.SYS, COMMAND.COM and an AUTOEXEC.BAT that would start your favorite word processor (WordStar of course :-D ).

[1] https://www.youtube.com/watch?v=0-X7Thsn0pI

justsomehnguy3• 4 months ago

I think the MS-DOS installer disk put files in C:\DOS by convention but that was just a convention.

Yes. For whatever reason my father used C:\SYS and I inherited it, along with C:\WIN for Windows.

wmf• 4 months ago

They could have had file permissions. They could have had a package manager instead of third-party installers.

Also note that Microsoft Office has a long history of not following Windows rules. Microsoft didn't even set a good example.

WaterRun• 4 months ago

In the era of Windows 95, having a network connection was still a rarity. Expecting modern systems to have package management and sandboxing mechanisms would have been 20 years ahead of their time.

hulitu4• 4 months ago

They had. Sort of. MS-DOS was a single user system. See attrib for details.

eviks3• 4 months ago

The biggest cause for this problem isn't lack of docs, but poor OS design. Like, why would you let apps change anything without restrictions to begin with? Of course, then you have to have some dumb hidden folder wasting space to restore the changes, and this "waste space for no good reason because we can't architect properly" is still a common issue

jasomill• 4 months ago

You're not wrong, but largely as a result of dubious architectural decisions made in the name of backwards compatibility and minimal hardware requirements, Microsoft sold 40 million copies of Windows 95 in its first year, compared to 300,000 copies of Windows NT 3.1.

Consider:

Windows 95 ran the vast majority of MS-DOS and Windows 3.1 applications with minimal performance loss, supported MS-DOS and Windows 3.x drivers for hardware that lacked 32-bit driver support, and ran acceptably on a 386 with as little as 4 MB RAM.

The properly architected Windows NT 3.1, released two years before Windows 95, had limited MS-DOS and Windows 3.1 application support, required NT-specific drivers for all hardware, and required 12 MB RAM to boot, 16 MB to do anything useful, and you really wanted a 486 for decent performance.

gzread3• 4 months ago

I agree. Why should the person who bought a computer be allowed to own it? Phone ecosystems got this the right way - the company that made the device owns it, and the person who bought it does not!

hulitu4• 4 months ago

back in those days.
You see all the wacky software that doesn't follow the rules properly, does whatever it wants, breaks things.

Just like today. Software is hard, software engineering even harder.

1970-01-01• 4 months ago

The sad lesson is to be both proactive and reactive if you want a clean environment. Trust, verify, and stick around to clean up someone else's mess after the fact.

phendrenad23• 4 months ago

Windows, especially old versions, were beautifully pragmatic. Think about the things that would need to exist on an open-source OS to match this functionality. You'd need to:

1. Convince people to distribute programs via installers.

2. Provide some way that installers can tell the OS that they're an installer (and not invent 5 different ways to do this!)

3. Convince the creators of installers to actually use that function.

4. Convince library creators to maintain backward compatibility (big ask).

5. Convince people to not fork said libraries, creating ambiguous upgrade paths.

6. If there are multiple distros, convince them all to use the same backup/restore format for libraries (and not treat their own favorite libraries as "special")

marcosdumay• 4 months ago

That's not exactly what Windows installers did.

They absolutely created 10 different ways to install software; they didn't really advertised they were an installer; the only backward compatible thing there are the MS libraries; there was no common backup/restore format.

Instead, the Unix people made a mechanism for random programs to use their own libraries and not touch the system one. In fact, Windows had one too, but most applications still decided they need to break the system.

phendrenad23• 4 months ago

One of the biggest pitfalls in understanding the world is interpreting everything as an absolute. If someone says "dogs have four legs", you might think "well, I saw a dog with three legs, so there's no value in the idea that dogs have four legs, and I'll conclude that if I see tracks from an animal that seems to have four legs, it's impossible to know if it's a dog or a giant centipede". It's a pernicious little quirk of our minds that we fall for this kind of thinking.

To wit. The idea that installers on Windows behaved the way I described is an interesting fact. The idea that a few installers did things in unusual ways is a much less interesting fact. Putting them on the same level robs you of the insight, and if this is a pattern then there are a lot of things you simply can't learn, because an exception could be found.

HeckFeck• 4 months ago

1-3 are covered by package managers in pretty much every Linux distro and BSD.

phendrenad23• 4 months ago

I think you misunderstand. 1-3 are not goals, they're steps to the goal. Linux and BSD have different goals from Windows.

justsomehnguy3• 4 months ago

2. Provide some way that installers can tell the OS that they're an installer (and not invent 5 different ways to do this!)

It is still blows my mind what to tell the distro flavour and version I still need to rely on the shell globbing.

iamcalledrob• 4 months ago

I love the naiveté of this approach.

Unlike <arbitrary heuristic>, it's so easy to reason about. I wish this kind of approach was still viable.

ruevs• 4 months ago

And 6-7 years later the `WinSxS` directory was born and these days it is tens of gigabytes.

`Dism.exe /online /Cleanup-Image /StartComponentCleanup /ResetBase`

In an administrator command prompt. You can thank me when it's finished ;-)

AgentME• 4 months ago

When I was a kid, I released a small GUI program online that I made with either VB6 or VB.NET. The program used the standard open-file dialog. When I created the installer for my program through VB's release wizard, there was a page where it pointed out that my program depended on a certain system library (because of the open-file dialog) and it asked me if I wanted to include that library in the installer. I think the default answer was yes, or maybe it wasn't but it sounded like an obvious thing to enable so I did it. Apparently this screwed over and broke open-file dialogs globally across Windows for everyone who wasn't on the same version of Windows as me. Whoops! It's too bad that VB had such a foot-gun in it, and that the article's workaround didn't save those users.

Grom_PE• 4 months ago

In my 25 years of using Windows I've grown so much disdain towards annoying, broken, slow installers that I started to instead extract them like zip archives, using various tools: 7-Zip, UniExtract, Observer plugin for Far Manager, sometimes even manual carving.

Most things just worked after being extracted like that. Some things needed a few registry entries, or regsvr32 some dll files.

uxp100• 4 months ago

Some components addressed this problem by providing their own installer for the component, and telling installers, “You are not allowed to install these component file directly. Instead, you must run our custom installer.

Aha, that’s why they do that.

Macha• 4 months ago

I find articles like this a good counter to the idea that typical software used to be better in the past (usually with an appeal to an idea that people were “real programmers” in those days and anything other than C as used in the 90s is a modern extravagance)

intensifier• 4 months ago

This existed until Windows XP but with different name and behavior. Only from Vista, they added permissions to restrict user and third party programs to modify system files easily.

thecaio• 4 months ago

wow. this is insane. never new such mechanic was ever remotely considered or possible. pretty neat

Windows 95 defenses against installers that overwrite a file with an older one

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