General :: Possible To Bypass NFS File Permissions By Using A User-space NFS Client?
Jul 4, 2011
There are some user-space based NFS clients (e.g. NFS Client library). Can I bypass file permissions by using such client? code...
Client1 uses usual NFS client (kernel-mode based) and user1@client1 can read only file1, but not file2.
As I understand, client1 sends uid in nfs request, server1 do a permissions check based on the request data. So, I suggest this is possible to have a client2:
Client2 uses user-space client, and hacker@client2 knows uids of user1 and user2; If he wants to read file1 he can send uid of user1; if he wants to read file2, he sends uid of user2.
I've been looking to get some torrent downloads running on school servers, but I obviously can't install a torrent client because I don't have root (and by extent, can't run anything requiring root privileges). Servers are running various versions of Red Hat (at least the x86_64 ones are, I don't want to recompile if I don't have to). Google has failed me thus far.
I want to simply mount an ext4 file-system onto a normal mount point in Ubuntu (/media/whereever), as read-writable for the current logged-in user, i.e. me.
I don't want to add anything into /etc/fstab, I just want to do it now, manually. I need super-user privileges to mount a device, but then only root can read-write that mount. I've tried various of the mount options, added it into fstab, but with no luck.
I am writing device driver in which i have to call callback function from kernel space, which are saving my data. But the callback functions are in userspace. While accessing them i am getting segmentation fault.
In a 32-bit system, max memory addressable is 4GB. Now Linux kernel does memory mapping division of 1GB for kernel address space and 3GB for user address space. That means 4GB of virtual address space is divided between kernel (1GB) and user (3GB).
Q1. All virtual mapping utilizes the available physical RAM without any division? I mean to say that if RAM is 512MB then a page in kernel space can lie any where RAM (leave aside old PCI dma accesses)? (How this fits to fact that kernel memory is non-pageble)
Q2. If a process is created in user space, it has visibility 4GB address space or 3GB address space?
Picture the following:On computer A, local user John (and John alone) has rwx access to file1.txtComputer B also has a local user account named John. If file1.txt was to be copied from computer A to computer B, would the user account John on computer B be able to access it?I guess this wouldn't work using two windows computers due to the User name / GUID relationship. Maybe linux has something similar?
I have Squid and Dans set up on a passthrough box with 2 nics, port 80 requestsEverything is working great. I need to know if there is a way to set up Dansguardian so that a user can enter a password on a blocked page to access it.
I have just installed Ubuntu on a machine at work and wondered how i can add a new user with the same permissions as the "main user"? I added a user via the "users&groups" gui but sorting permissions looks tricky.
We are using thin client systems in our work environment. There is a central ubuntu server and by using thin clients, we are connecting to our homes. The problem is when I try to install an application, it reported me that I had 200 mb of disk space. But when i try to look from console, I see that /home folder has over 250 gb s of disk space. Even when I try to look from baobab, Disk Usage Analyzer in Ubuntu, i see that my home file system is full.
So what's the reason that I am receiving different kinds of disk space report from different sources? Our system admin here told me that some applications foolishly try to see the physical devices on the thin client and got confused as a result. Is this true?
I am developing a I2C CDROM client driver. The CDROM firmware supports TOC information read through a I2C command. It sends the TOC information in burst ( Interrupts a GPIO pin when it is ready ) and my CPU does a I2C read to read the TOC. When the CDROM firmware finishes sending the last data burst , it informs my CPU that it is done with the TOC, by a flag in the last data burst. I would like to know, which is the most efficinet way I can send these TOC information to userspace?
I wanna write a file in kernel space but from my searching I can to know that instead of writeing file in kernel space ,I can write data to user space by copy_to_user space.
But link is missing ...I dont know how will my user space will access kernel space means my function in kernel space which will do copy_to_user /....How my user space function will call my kernel level function ..
Can any one of you provide me with some example file which are doing this .I know every char driver is using it ...but i could not trace back how user level function is accessing it ...i m confused between user space and kernel space.
I am doing rhce course but i am very confused to answer these user and group permissions.the questions are like this...the owner of the /data must be user tom.primary group of /data must be the group sysadmins.the members of the group test must be able to write and create files in the /data.the members of the group web have no access to these directory.the user jack not belong to any of these gropus must have to edit files created in /data.the user tim can only list the contents.
the questions are always like these..i am okay with sgid and sticky bit.but i dnt know where to set default acl and other permissions.
I want to make sure that the user www-data cannot be used to login on my system (Ubuntu Lucid). How can I find out? - is there a command I can run against this user? (traditionally run by Apache daemon)
I have the following requirement in my module. The driver gets some data from the external device. After getting 1MB of data it has to send it to the user space application. What is the best thing to implement for this in driver.? Is it ok to implement like, after getting data, the driver will send a signal to the user space application. Then the user space application sends an ioctl to read the data. Is there any alternate, that the driver directly sends the data without the user space application asks for it.?
I'm beginning to deal with more than one user on my system (it's a VPS serving some sites) and I need to make sure I understand how group permissions work. I have an account named "admin" .. it's basically the primary account that is used for serving most of the sites that I control myself. Now, I added a second account named "Ville" as one of my users wants to be able to administer that site. So, I can do this the easy way and just chown their domains folder under the ville user, they have permission to do whatever they need be and so forth. However, let's say I want to also give the admin user access to the files (modifying and all) .. how can I put both users into the same group and give them both permission?
I've tried doing: sudo usermod -a -G admin ville To add the ville into the admin group, but ville still cannot edit files by admin. Permissions for the primary directory for the ville user are read/write for both owner and group, and the current group for the files is admin:admin .. But ville still can't write into the directory. So, what should I be doing here to get this right and secure at the same time?
I am trying to setup 2 individual FTP users. They should both have access to the same directory. They both need to be able to read/write into the directory. But, I want them not to be able to write to each other's files (e.g. delete, remove, rename, etc.).
So let's say the shared directory is: /home/ftp/shared/
UserA needs read/write access to /home/ftp/shared/. UserA should only have write access to his own files. UserB also needs read/write access to /home/ftp/shared/. UserB should only have write access to his own files.
It would be a unix box of sorts, but that is the only restriction. I could use whatever software. I am currently thinking pure-ftpd or vsftp but I am open to all ideas.
On my laptop I have a dual boot system, CentOS 5.4 on one partition and Windows Vista on the other. In Windows, I have a program installed that allows me to access my linux partition so I have access to the files. Every time I boot into linux after accessing the linux partition through windows, I get a forced file system check. I was wondering if there is a way to disable or perhaps bypass this check?
I hope this is the right place to post to because I haven't found any other related forums.I'm working on an AMD opteron running Linux 22.214.171.124 I want to preload a hardware performance counter (register) with a value to have it overflow after a number of a specific event counts. As I understand, when the counter in the register overflows, an interrupt will be generated and handled by the appropriate interrupt handler. How can my user-level application get notified whenever the interrupt occurs? I want to obtain information on the instruction that caused the overflow. Is this possible? I think this is different than responding to signals with sigaction().