![Eric W. Biederman](/assets/img/avatar_default.png)
There is no backing store to ramfs and file creation rules are the same as for any other filesystem so it is semantically safe to allow unprivileged users to mount it. The memory control group successfully limits how much memory ramfs can consume on any system that cares about a user namespace root using ramfs to exhaust memory the memory control group can be deployed. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
291 lines
6.7 KiB
C
291 lines
6.7 KiB
C
/*
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* Resizable simple ram filesystem for Linux.
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*
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* Copyright (C) 2000 Linus Torvalds.
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* 2000 Transmeta Corp.
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*
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* Usage limits added by David Gibson, Linuxcare Australia.
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* This file is released under the GPL.
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*/
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/*
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* NOTE! This filesystem is probably most useful
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* not as a real filesystem, but as an example of
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* how virtual filesystems can be written.
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*
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* It doesn't get much simpler than this. Consider
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* that this file implements the full semantics of
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* a POSIX-compliant read-write filesystem.
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*
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* Note in particular how the filesystem does not
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* need to implement any data structures of its own
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* to keep track of the virtual data: using the VFS
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* caches is sufficient.
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*/
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#include <linux/fs.h>
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#include <linux/pagemap.h>
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#include <linux/highmem.h>
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#include <linux/time.h>
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#include <linux/init.h>
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#include <linux/string.h>
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#include <linux/backing-dev.h>
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#include <linux/ramfs.h>
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#include <linux/sched.h>
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#include <linux/parser.h>
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#include <linux/magic.h>
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#include <linux/slab.h>
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#include <asm/uaccess.h>
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#include "internal.h"
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#define RAMFS_DEFAULT_MODE 0755
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static const struct super_operations ramfs_ops;
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static const struct inode_operations ramfs_dir_inode_operations;
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static struct backing_dev_info ramfs_backing_dev_info = {
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.name = "ramfs",
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.ra_pages = 0, /* No readahead */
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.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK |
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BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
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BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
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};
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struct inode *ramfs_get_inode(struct super_block *sb,
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const struct inode *dir, umode_t mode, dev_t dev)
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{
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struct inode * inode = new_inode(sb);
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if (inode) {
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inode->i_ino = get_next_ino();
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inode_init_owner(inode, dir, mode);
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inode->i_mapping->a_ops = &ramfs_aops;
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inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
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mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
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mapping_set_unevictable(inode->i_mapping);
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inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
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switch (mode & S_IFMT) {
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default:
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init_special_inode(inode, mode, dev);
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break;
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case S_IFREG:
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inode->i_op = &ramfs_file_inode_operations;
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inode->i_fop = &ramfs_file_operations;
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break;
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case S_IFDIR:
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inode->i_op = &ramfs_dir_inode_operations;
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inode->i_fop = &simple_dir_operations;
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/* directory inodes start off with i_nlink == 2 (for "." entry) */
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inc_nlink(inode);
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break;
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case S_IFLNK:
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inode->i_op = &page_symlink_inode_operations;
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break;
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}
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}
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return inode;
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}
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/*
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* File creation. Allocate an inode, and we're done..
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*/
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/* SMP-safe */
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static int
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ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
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{
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struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
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int error = -ENOSPC;
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if (inode) {
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d_instantiate(dentry, inode);
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dget(dentry); /* Extra count - pin the dentry in core */
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error = 0;
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dir->i_mtime = dir->i_ctime = CURRENT_TIME;
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}
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return error;
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}
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static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
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{
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int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
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if (!retval)
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inc_nlink(dir);
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return retval;
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}
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static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
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{
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return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
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}
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static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
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{
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struct inode *inode;
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int error = -ENOSPC;
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inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
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if (inode) {
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int l = strlen(symname)+1;
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error = page_symlink(inode, symname, l);
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if (!error) {
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d_instantiate(dentry, inode);
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dget(dentry);
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dir->i_mtime = dir->i_ctime = CURRENT_TIME;
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} else
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iput(inode);
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}
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return error;
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}
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static const struct inode_operations ramfs_dir_inode_operations = {
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.create = ramfs_create,
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.lookup = simple_lookup,
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.link = simple_link,
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.unlink = simple_unlink,
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.symlink = ramfs_symlink,
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.mkdir = ramfs_mkdir,
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.rmdir = simple_rmdir,
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.mknod = ramfs_mknod,
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.rename = simple_rename,
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};
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static const struct super_operations ramfs_ops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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.show_options = generic_show_options,
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};
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struct ramfs_mount_opts {
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umode_t mode;
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};
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enum {
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Opt_mode,
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Opt_err
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};
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static const match_table_t tokens = {
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{Opt_mode, "mode=%o"},
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{Opt_err, NULL}
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};
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struct ramfs_fs_info {
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struct ramfs_mount_opts mount_opts;
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};
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static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
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{
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substring_t args[MAX_OPT_ARGS];
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int option;
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int token;
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char *p;
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opts->mode = RAMFS_DEFAULT_MODE;
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while ((p = strsep(&data, ",")) != NULL) {
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if (!*p)
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continue;
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token = match_token(p, tokens, args);
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switch (token) {
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case Opt_mode:
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if (match_octal(&args[0], &option))
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return -EINVAL;
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opts->mode = option & S_IALLUGO;
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break;
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/*
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* We might like to report bad mount options here;
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* but traditionally ramfs has ignored all mount options,
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* and as it is used as a !CONFIG_SHMEM simple substitute
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* for tmpfs, better continue to ignore other mount options.
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*/
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}
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}
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return 0;
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}
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int ramfs_fill_super(struct super_block *sb, void *data, int silent)
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{
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struct ramfs_fs_info *fsi;
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struct inode *inode;
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int err;
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save_mount_options(sb, data);
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fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
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sb->s_fs_info = fsi;
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if (!fsi)
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return -ENOMEM;
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err = ramfs_parse_options(data, &fsi->mount_opts);
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if (err)
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return err;
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sb->s_maxbytes = MAX_LFS_FILESIZE;
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sb->s_blocksize = PAGE_CACHE_SIZE;
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sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
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sb->s_magic = RAMFS_MAGIC;
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sb->s_op = &ramfs_ops;
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sb->s_time_gran = 1;
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inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
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sb->s_root = d_make_root(inode);
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if (!sb->s_root)
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return -ENOMEM;
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return 0;
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}
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struct dentry *ramfs_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data)
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{
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return mount_nodev(fs_type, flags, data, ramfs_fill_super);
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}
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static struct dentry *rootfs_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data)
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{
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return mount_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super);
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}
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static void ramfs_kill_sb(struct super_block *sb)
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{
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kfree(sb->s_fs_info);
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kill_litter_super(sb);
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}
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static struct file_system_type ramfs_fs_type = {
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.name = "ramfs",
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.mount = ramfs_mount,
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.kill_sb = ramfs_kill_sb,
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.fs_flags = FS_USERNS_MOUNT,
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};
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static struct file_system_type rootfs_fs_type = {
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.name = "rootfs",
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.mount = rootfs_mount,
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.kill_sb = kill_litter_super,
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};
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static int __init init_ramfs_fs(void)
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{
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return register_filesystem(&ramfs_fs_type);
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}
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module_init(init_ramfs_fs)
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int __init init_rootfs(void)
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{
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int err;
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err = bdi_init(&ramfs_backing_dev_info);
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if (err)
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return err;
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err = register_filesystem(&rootfs_fs_type);
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if (err)
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bdi_destroy(&ramfs_backing_dev_info);
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return err;
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}
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