Secure-garbage-file-system

Developed a stackable file system to asynchronously delete and move the files to a trash bin. Files in trash bin folder are secured, compressed, encrypted and can be restored by user.

• PURPOSE:

To become familiar with the VFS layer of Linux, and especially with extensible file systems APIs. To build a useful file system using stacking technologies.

• INTRODUCTION:

In a stackable file system, each VFS-based object at the stackable file system (e.g., in Wrapfs) has a link to one other object on the lower file system (sometimes called the "hidden" object). We identify this symbolically as X->X' where "X" is an object at the upper layer, and X' is an object on the lower layer. This form of stacking is a single-layer linear stacking.

*IMPORTANT COMMANDS/THINGS TO NOTE:

-Please give permission to create .sg folder accessible to all other users this can be done by -umask 0011 or 0000

-Run the Makefile in hw2 folder to create object file for sgctl.c

-Run the following command to make the fs/sgfs modules. make modules SUBDIRS=fs/sgfs/ make modules_install SUBDIRS=fs/sgfs/

-Unmount anyother file system umount /mnt/sgfs

-Remove anyother sgfs mounted rmmod sgfs

-Install the new make of sgfs insmod ./fs/sgfs/sgfs.ko

-Mounting sgfs can be done as follows:

mount -t sgfs /some/lower/path /mnt/sgfs

or

mount -t sgfs -o key=MySecretPa55 /some/lower/path /mnt/sgfs

-To undelete a file give the following command $ PATH_TOSGCTL/sgctl -u FILE

FILE: the file's name to undelete -u: option to "undelete"

*LIST OF FILES ADDED:

/usr/src/hw2-user/fs/sgfs -dentry.c -file.c(modified) -inode.c(modified) -lookup.c -main.c(modified) -sgfs.h(modified) -mmap.c -sgfs.mod.c -super.c

/usr/src/hw2-user/hw2 -README(modified) -sgctl.c -Makefile -kernel.config

/usr/src/hw2-user/ -compile.sh

Other files modified

magic.h(modified) fs/Kconfig(modified) fs/Makefile(modfied)

• DETAILS(Algorithm)

I. During mount two functions were modified :- sgfs_mount():-

• void *raw_data was parsed to get the key, and check if it is passed or not sgfs_read_super():-
• To create .sg folder at mount path (obtained from variable dev_name)
• using SGFS_SB(sb) struct sgfs_sb_info was obtained.
• Information of key and mount path is stored in this struct sgfs_sb_info,

II. To delete a file :- SGFS_UNLIK -Get user id of current user -Check if the file is .sg folder(using complete paths, mount path(obtained from Superblock private_info) and file path from d_path) - from the file name check if the file owner(first 4 bytes) is same as current user. - If it is same delete the file - Else return -EPERM error -Check if the key was supplied during mount option(this information is stored in Superblock of fs) -If No key was supplied -Then rename the file to .sg folder -Else - Encrypt the content of file and write to a new file in .sg folder - If the encryption of writing fails in between - Unlink the new file created and restore the dentry of the file which was supposed to be deleted using d_drop - Else -Unlink the old file -Sync the upper level obejcts with lower level objects. -Free all the buffers

III. To undelete a file :-

• A user program .sgctl was created that will call sgfs_unlock_ioctl() function
• User program passed a file descriptor to kernel
• Get the lower file descriptor using funcion sgfs_get_lower()
• Check if the file is .sg folder(using complete paths, mount path(obtained from Superblock private_info) and file path from d_path)
• If it is .sg folder
• from the file name check if the file owner(first 4 bytes) is same as current user.
• If it is same
  • Extract the original name of the file
  • Check the extension of the file
  • If extension is .enc
    • Rename it to CWD
  • Else
    • Encrypt the content of file and write to a new file in .sg folder
  • If the encryption of writing fails in between
    • Unlink the new file created and restore the dentry of the file which was supposed to be deleted using d_drop
  • Else -Unlink the old file -Sync the upper level obejcts with lower level objects. -Free all the buffers

IV. To List the files in .sg folder

• sgfs_readdir function was modified. and a new my_filldir() function is created
• Create a global struct dir_context and store the context received in this global variable.
• Create another new struct dir_context with actor function pointing to my_filldir() my_filldir()
  • from the file name check if the file owner(first 4 bytes) is same as current user.
  • If it is same
  • call and the actor of the original context using global dir_context
  • Else return 0
• If ls is issued in .sg folder
  • the call iterdir with new dir_context
• Else call iterdir with the old dir_context

REFERENCES:-

https://elixir.bootlin.com/linux/v3.2.29/source/fs/char_dev.c http://lxr.fsl.cs.sunysb.edu/linux/source/kernel/audit.c#L1658 https://github.com/richygerard/file-encryption-decryption/