Discussion

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

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

akdev1l: >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.

calgarymicro: > 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 highjacking the OS to perpetually rewrite its own system components back to compromised version number ∞ whenever another installer tries to clean things up.

bombcar: > 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.

akdev1l: 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.

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

layer8: The latter, according to https://devblogs.microsoft.com/oldnewthing/20260324-00/?p=11...

chihuahua: 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.

layer8: > 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.

elzbardico: 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.

elzbardico: Man, after looking at the veritable pile of stinking matter that is claude code, compare it with the NT 4 source leak.Windows may have suffered its share of bad architectural decisions, but unhinged is a word that I wouldn't apply to their work on Windows.

phendrenad2: [delayed]

1970-01-01: 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.

topspin: 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.

marcosdumay: 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.

kstrauser: > So Microsoft had to do everything they could to ensure broken software would still workI 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.

rkagerer: This is truly unhingedGranted, 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.

bigstrat2003: 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.

Legend2440: >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.

jjmarr: > 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".

anonymars: Yes, but that doesn't solve the customer's problemAnd what does the customer do if the vendor has discontinued it? Or charges for an upgrade? Or has gone out of business?https://devblogs.microsoft.com/oldnewthing/20031224-00/?p=41...

acuozzo: > After a few years of pain, people would've gotten with the program, so to speak.Not necessarily. This was still very much the time in which choosing to stick with an old version which worked (e.g. Windows 3.1) wasn't uncommon.Just look at how many people jumped from XP to 7 due to the network effect of "Vista sucks" and then multiply that by the fact that, at the time of 3.1->95, people had far fewer computer security concerns, if any.

adrian_b: Windows 95 was not Windows NT and it still used the FAT32 file system, where it was not really possible to enforce access rights.As TFA says:You even had installers that took even more extreme measures and said, “Okay, fine, I can’t overwrite the file, so I’m going to reboot the system and then overwrite the file from a batch file, see if you can stop me.”

badsectoracula: TBH i think a more likely explanation is that they needed to somehow identify separate instances of that data structure and they thought to store some ID or something in it so that when they encountered it next they'd be able to do that without keeping copies of all the data in it and then comparing their data with the system's.

topspin: ^^ The voice of experience, here.

badsectoracula: The thing is, Microsoft got its position of dominance exactly because they did that - and that was because by doing this, the users' programs kept working. Remember that users outnumber developers by far and the last thing Microsoft wanted was for people to not upgrade Windows because they broke their previously working programs.This was even more important at a time when Microsoft had actual competition in the OS space and people weren't able to just go online and download updates.

Krutonium: IIRC Sim City 2000 is one such piece of software.

topspin: > And what does the customer do if the vendor has discontinued it? Or charges for an upgrade? Or has gone out of business?Those problems can all be filed under Not My Problem (as in, Microsoft's problem,) and safely ignored. On the other hand, when Highly Influential So-And-So upgrades from 3.1 to 95 or whatever, and Very Population Application v4.9.6 starts falling over, Microsoft gets the black eye whether they deserve it or not. The whole equation changes.

BearOso: [delayed]