What I need, boiled down, is a way to 'selectively' encrypt either a folder or a zip file - Whatever the solution would be, it needs to block (or redirect) all reads/writes EXCEPT from one specific program (not mine, a legacy application that I do not have source code access to - I cannot modify the program who would have the sole permission to perform reads and writes on the encrypted folder/zip file). I would like to avoid having a constantly running background app (as all the end-user would have to do to circumvent the protection would be to kill the program)
The purpose is to, of course, protect the files within the folder from tampering.
I could modify folder permissions at install, but this would block all programs from access wouldn't it? I more or less need to only block File Explorer from accessing the files, but not the program which needs to read them... if that makes sense. Or, if I could protect the (plaintext) files somehow without affecting the legacy application's reading of them... argh.
I wonder if it would be possible with CreateProcess() to run the legacy application as a high-level user and give the folders it needs access to the same permission, such as TrustedInstaller or SYSTEM, (who, in Windows, own things that not even administrators can touch, like System Volume Information)
This would allow the program to read/write to the folders, but not the user.
I was looking at LockFile, seems to be close to what I am looking for but not quite. I need something like semi-exclusive access.
I am fairly fluent in C++, Visual Basic.net, only some Python, but I am willing to use any language which would allow a solution to this problem (Though it probably could be implemented in any language, if possible at all.)
Related
Hi
I was trying to use FileSystemWatcher to detect if some files or directories has been moved to another location. The problem was, i had to use onCreated and onDeleted events to handle this, but there are many issues using this solution
how could i detect change if i will select more than one file and press Ctrl+C, Ctrl+V, or right-click and select Copy and then Paste in the same directory?
how could i detect, if i will select more than one directory?
the last one, what if i simulate moving file? I could delete file and create with same name in different place.
I know i could use, Timers, process locking detection, verification which process uses file (if explorer.exe then it could be moving file), but this solution is not perfect and it's very ineffective. I was whinking about this how to solve this issue, and i have decided to implement this in low-level language. Is this possible to do this using C, or assembler? I know that every thing is possible to do using assembler, so is it possible to implement this in asm? I would like to create my own FileSystemWatcher using assembler or C but where should i looking for info how to do this?
File movement within the same filesystem can be detected easily using a filesystem filter driver, as the filesystem received the corresponding request from the OS. Other scenarios such as moving to the other disk or moving by copy/delete sequence are hardly traceable even with the filter driver because you would need to match between the file which have been created/written to and the file which is being deleted (possibly on the other disk).
If you plan to write some security mechanism (like a DRM), then I need to remind that the data can be altered during copying (eg. encrypted or compressed), which makes your task even harder.
Still you can look at filesystem filter drivers - should you decide to go on with detection of filesystem events, such driver is a much more reliable and powerful mechanism than FileSystemWatcher.
Is it possible to use a set of C library or system calls to drop all user privileges on POSIX, or at least on Linux? Note that I am not asking how to drop root privileges, which is what all of the other StackOverflow search results seem to be asking and answering.
I want the same effect as switching to user nobody, but stronger if possible. That is, I want my C application to do the following:
Run as a normal user, not root, and without the setuid file permission bit
Retain the ability to access specific files and open outgoing network connections
Voluntarily and permanently lose the ability to read and write files in specified (or all) directories, especially $HOME
If possible, give up or sandbox all other nonessential abilities, like opening a listening socket with accept
Things I have considered so far that don't fit the bill:
Switching to user nobody with setuid/setgid
Ordinary users are forbidden from switching to other users (like nobody), and the application should not require root just to switch to nobody.
Linux/POSIX.1e Capabilities
Capabilities only add root-like privileges, not take away ordinary user privileges
Traditional seccomp
My application will need more than just exit, sigreturn, read, and write
Things that look interesting, but for which I couldn't find documentation, appear to be unmaintained, or appear to be non-portable:
seccomp-bpf
AppArmor
grsecurity RBAC/role-based access control
So is there a well-documented, preferably portable way to drop nonessential user privileges and sandbox a process without having to become root first?
It's unlikely any solution will work on all POSIX, since POSIX doesn't define the mechanism you're looking for.
Looking at just the requirements and just Linux, probably the easiest way to satisfy them is actual via the security modules. Any of apparmor, selinux, RBAC will do what you need, but only via external profile - not something built into your app. The problem may be that adding a profile in all those cases requires the root user to do it (but the profile applies to user process too).
A bit more complicated solution that almost satisfies the requirements is seccomp. While it doesn't understand paths at all (you can only see pointers), there are ways to limit the access: seccomp policies can be defined per thread, so you could redesign your system to have a "path verification thread", which doesn't do anything apart from reading paths and returning sockets if they match your specification. Then limit that thread to just recv(), open() and send(). Thread doing other work can then drop open() and use the other service.
Or if you can configure the paths at program startup, you can put them into an array, mark that page as read-only, and setup seccomp policy which will only accept open() with filenames from that array (that's just a pointer comparison in that case).
To some extent, the approach of splitting application into separate processes which have very limited responsibilities is something you could replicate on other systems, but without the same guarantees as on Linux. For example qmail is kind of a system of very small processes which work as a pipeline for data (simplification). On Linux you could still apply seccomp to them, on Solaris just drop exec and other capabilities, on other systems... I don't know, but probably you can do something.
I was wondering, I am writing a program in C, and I writing the output from my program to a csv file. This works locally, and I can create and update the file with no errors.
But on the server, where I need to store the file - I do not have permissions to write to that file/directory. Is there a work around for getting around the permissions problems?
Well, you can run your program as a more authorative user, such as root.
There is no simple way from the program itself to just ignore the operating system's security model, that would make it quite pointless.
Note that if you're not the administrator on the server, you're likely not even allowed to run programs as root.
Finally, writing C programs that manipulate files and directories and then running them as root on a server is a fine way of shooting yourself in the foot. Be careful.
Hello all I have some very important system files which I want to protect from accidental deletion even by root user. I can create a new partition for that and mount it with readonly access but the problem is that I want my application which handles those system files to have write access to that part and be able to modify them. Is that possible using VFS? As VFS handles access to the files I could have a module inserted in the VFS layer which can see if there is a write access to that part then see the authorization and allow it or otherwise reject it.
If not please provide me suggestions regarding how can such a system be implemented what would I need in that case.
If there exists a system like this please suggest about them also.
I am using linux and want to implement this in C, I think it would be possible in C only.
Edit: There are such kind of programs implemented in windows which can restrict access to administrator even, to some important folders, would that be possible in linux?
My application is a system backup and restore program which needs to keep its backup information safe and secure. So I would like to have a secured part of a partition which could not be accidently deleted in any way. There are methods of locking a flashdrive can we use some of those methods for locking a partition in linux also ? so that mount is password protected ? I am not writing a virus application, my application would give user option to delete the backups but I don't wanna allow them to be deleted by any other application.
Edit: I am writing a system restore and backup program for ubuntu, I am a computer engineering student.
Edit: As I have got opinion from Basile Starynkevitch that I would be committing worst sin of programming if I do anything like this, but you could provide me suggestions considering this as a experimental project, I could make some changes in the VFS layer so that this could work.
You could use chattr, e.g.
chattr +i yourfile
But I don't think it is a good thing to do that. People using root access are expected to be careful. Those having root access can still issue the command undoing the above.
There is no way to forbid people having root access, or people having physical access to the computer, to access, remove, change your file, if they really want to (they could update & hack the kernel, for instance). Read more about trusted compute base
And I believe it is even unethical (and perhaps illegal, in some countries) to want to do that. I own my PC, and I don't understand why you should disallow me to change some data on it, because I happened to install some software.
By definition of root on Linux, it can do anything... You won't be able to prohibit him to erase or alter data... People with root access can write arbitrary bytes at arbitrary places on the disk.
And on a machine that I own (or perhaps just have physical access to), I will, thanks God, always be able to remove a file (even under Windows: I could for example boot a Linux CDROM and remove the file from Linux accessing an NTFS, and then reboot the Windows...).
So I think you should not bother and take even a minute to find out how to make root altering your precious files more difficult. Leave them as other root files...
PHILOSOPHICAL RANT
The unix philosophy has always been to trust the system administrator (while protecting newbie users from mistakes), that is the root user. The root is able to do anything (this is why people avoid being root, even on a personal machine). There have never been strong features to prohibit root doing mistakes, because the system administrator is expected to know well the system, and is trusted.
And Unix sysadmins understand this fact: it is part of their culture. (This is probably in contrast with Windows administration culture). They know when to be careful, they don't expect software to prevent mistakes as root.
In order to use root squashing (which makes it so that root can't even see files for a local user) you can set up a local nfs. This forum page explains how to mount an nfs locally. The command is:
mount -t nfs nameofcomputer:/directory_on_that_machine /directory_you_should_have_already_created
nfs has root squashing enabled by default, which should solve your problem. From there, you just make sure your program stores its files on the nfs mount.
Sounds to me like you're trying to write a virus.
No doubt you will disagree.
But I'm willing to bet the poor people that install your software will feel like it's a virus, because it will be behaving like one by making itself hard to remove.
Simply setting r/w flags should suffice for anything else.
I am allowing users to upload photos like photo albums, and also attach files (documents for now) as mail attachments. So i assume I need some anti virus/security tool in place to scan the files first in case people upload infected stuff. So two questions:
1) Are there any 'free' or open source tools for this I can use or integrate into my environment: codeignitor php?
2) How to secure the upload area from rest of the system? Say the virus scanner fails to catch a virus and it is uploaded, how to prevent it from infecting other files? Like can the upload area be sandboxed in or something always and use that filepath for users to access the content so it does not spread to other parts of the system?
There is clamav for a free virus scanner. Install it and you could do something like:
function virus_detected($filename)
{
$clamscan = "/usr/local/bin/clamscan";
$result = exec("$clamscan -i --no-summary $filename");
return strlen($result)?true:false;
}
As for security, make sure the temporary files are uploaded to a directory outside of your web root. You should then verify the file type, rename the file to something other than it's original file name and append the appropriate extension (gif,jpg,bmp,png). I believe this should keep you fairly safe aside from exploits in php itself.
For more information about verifying file types in php check out:
http://www.php.net/manual/en/function.finfo-file.php
I know this topic hasn't been active for three years now, but, in case anyone else in the future, similarly, is looking for a PHP-based anti-virus solution, for those without an anti-virus daemon, program or utility installed on their host machine and without the ability to install an anti-virus daemon, program or utility, phpMussel, a PHP script that I've written based on ClamAV that fits the bill for what Rohit (the the original poster) was looking for (a PHP-based anti-virus to protect their CMS against malicious file uploads), may possibly be a viable solution. It certainly isn't perfect and I can't guarantee that it'll catch everything, but by far, it's certainly better than using nothing at all.
Ideally, as per already suggested above by Matt, making a call to shell to have ClamScan scan the file uploads is definitely an ideal solution, and if this is something that a hostmaster, webmaster or anyone in Rohit's situation is able to do, I'd second that suggestion wholly. What I've written, because it is a PHP script, has limitations inherent to anything that relies wholly on PHP in order to function, but, in instances where the aforementioned suggestion and/or similar suggestions aren't a possibility (such as if the host machine doesn't have an anti-virus installed and shell access is disabled; common with cheaper shared hosting solutions), that's where what I'm suggesting here could potentially step in - Something that only requires PHP to be installed (with PCRE extension included, which is standard with PHP nowadays anyhow), and nothing more.
Also remember, as Matt has already suggested, to always upload outside of your root directory, to ensure that uploaded files can't be exploited by attackers (such as in the event of an attacker attempting to compromise your system by uploading backdoors or trojans) - Viruses are not the only threat you need to worry about, and the vast majority of anti-virus solutions nowadays do not solely focus on viruses. Matt is also entirely correct in pointing out that no anti-virus solution is perfect, and for that reason, anyone allowing file uploads to their website or server needs to remain vigilant - An anti-virus solution is a must-have for anyone in that situation, but no holy grail of internet security that'll cover every possible threat exists. Also, renaming files isn't only about ensuring that they can't execute (as may be somewhat inferred by the original poster's reply comment regarding EXEs) - The risk of threats such as directory traversal attacks can be reduced by renaming files as well as the risk associated with an attacker attempting to override an already existing file on a targeted system as a means to hide their dirty-work.
Regarding the threat of files that may be malicious being missed by an anti-virus solution and then potentially infecting the system where they are being uploaded to; What a hostmaster or webmaster could potentially do in this situation is employ some sort of quick and simple encoding process that'd render the file non-executable by the system itself, but which can be easily and readily reversed by the PHP script responsible for calling that file on request, such as by way of using base64_encode(), bin2hex(), or even by just rotating a few characters and adding a salt to displace the file's magic number or something similar.