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![Eric W. Biederman](/assets/img/avatar_default.png)
Modify the request_module to prefix the file system type with "fs-" and add aliases to all of the filesystems that can be built as modules to match. A common practice is to build all of the kernel code and leave code that is not commonly needed as modules, with the result that many users are exposed to any bug anywhere in the kernel. Looking for filesystems with a fs- prefix limits the pool of possible modules that can be loaded by mount to just filesystems trivially making things safer with no real cost. Using aliases means user space can control the policy of which filesystem modules are auto-loaded by editing /etc/modprobe.d/*.conf with blacklist and alias directives. Allowing simple, safe, well understood work-arounds to known problematic software. This also addresses a rare but unfortunate problem where the filesystem name is not the same as it's module name and module auto-loading would not work. While writing this patch I saw a handful of such cases. The most significant being autofs that lives in the module autofs4. This is relevant to user namespaces because we can reach the request module in get_fs_type() without having any special permissions, and people get uncomfortable when a user specified string (in this case the filesystem type) goes all of the way to request_module. After having looked at this issue I don't think there is any particular reason to perform any filtering or permission checks beyond making it clear in the module request that we want a filesystem module. The common pattern in the kernel is to call request_module() without regards to the users permissions. In general all a filesystem module does once loaded is call register_filesystem() and go to sleep. Which means there is not much attack surface exposed by loading a filesytem module unless the filesystem is mounted. In a user namespace filesystems are not mounted unless .fs_flags = FS_USERNS_MOUNT, which most filesystems do not set today. Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Acked-by: Kees Cook <keescook@chromium.org> Reported-by: Kees Cook <keescook@google.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
333 lines
7.3 KiB
C
333 lines
7.3 KiB
C
/*
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* Super block/filesystem wide operations
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*
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* Copyright (C) 1996 Peter J. Braam <braam@maths.ox.ac.uk> and
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* Michael Callahan <callahan@maths.ox.ac.uk>
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*
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* Rewritten for Linux 2.1. Peter Braam <braam@cs.cmu.edu>
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* Copyright (C) Carnegie Mellon University
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*/
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/string.h>
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#include <linux/stat.h>
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#include <linux/errno.h>
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#include <linux/unistd.h>
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#include <linux/mutex.h>
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#include <linux/spinlock.h>
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#include <linux/file.h>
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#include <linux/vfs.h>
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#include <linux/slab.h>
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#include <linux/pid_namespace.h>
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#include <asm/uaccess.h>
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#include <linux/fs.h>
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#include <linux/vmalloc.h>
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#include <linux/coda.h>
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#include <linux/coda_psdev.h>
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#include "coda_linux.h"
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#include "coda_cache.h"
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#include "coda_int.h"
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/* VFS super_block ops */
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static void coda_evict_inode(struct inode *);
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static void coda_put_super(struct super_block *);
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static int coda_statfs(struct dentry *dentry, struct kstatfs *buf);
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static struct kmem_cache * coda_inode_cachep;
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static struct inode *coda_alloc_inode(struct super_block *sb)
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{
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struct coda_inode_info *ei;
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ei = kmem_cache_alloc(coda_inode_cachep, GFP_KERNEL);
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if (!ei)
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return NULL;
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memset(&ei->c_fid, 0, sizeof(struct CodaFid));
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ei->c_flags = 0;
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ei->c_uid = GLOBAL_ROOT_UID;
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ei->c_cached_perm = 0;
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spin_lock_init(&ei->c_lock);
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return &ei->vfs_inode;
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}
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static void coda_i_callback(struct rcu_head *head)
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{
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struct inode *inode = container_of(head, struct inode, i_rcu);
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kmem_cache_free(coda_inode_cachep, ITOC(inode));
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}
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static void coda_destroy_inode(struct inode *inode)
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{
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call_rcu(&inode->i_rcu, coda_i_callback);
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}
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static void init_once(void *foo)
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{
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struct coda_inode_info *ei = (struct coda_inode_info *) foo;
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inode_init_once(&ei->vfs_inode);
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}
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int coda_init_inodecache(void)
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{
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coda_inode_cachep = kmem_cache_create("coda_inode_cache",
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sizeof(struct coda_inode_info),
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0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD,
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init_once);
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if (coda_inode_cachep == NULL)
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return -ENOMEM;
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return 0;
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}
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void coda_destroy_inodecache(void)
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{
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/*
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* Make sure all delayed rcu free inodes are flushed before we
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* destroy cache.
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*/
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rcu_barrier();
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kmem_cache_destroy(coda_inode_cachep);
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}
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static int coda_remount(struct super_block *sb, int *flags, char *data)
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{
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*flags |= MS_NOATIME;
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return 0;
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}
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/* exported operations */
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static const struct super_operations coda_super_operations =
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{
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.alloc_inode = coda_alloc_inode,
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.destroy_inode = coda_destroy_inode,
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.evict_inode = coda_evict_inode,
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.put_super = coda_put_super,
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.statfs = coda_statfs,
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.remount_fs = coda_remount,
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};
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static int get_device_index(struct coda_mount_data *data)
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{
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struct fd f;
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struct inode *inode;
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int idx;
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if (data == NULL) {
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printk("coda_read_super: Bad mount data\n");
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return -1;
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}
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if (data->version != CODA_MOUNT_VERSION) {
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printk("coda_read_super: Bad mount version\n");
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return -1;
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}
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f = fdget(data->fd);
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if (!f.file)
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goto Ebadf;
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inode = file_inode(f.file);
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if (!S_ISCHR(inode->i_mode) || imajor(inode) != CODA_PSDEV_MAJOR) {
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fdput(f);
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goto Ebadf;
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}
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idx = iminor(inode);
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fdput(f);
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if (idx < 0 || idx >= MAX_CODADEVS) {
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printk("coda_read_super: Bad minor number\n");
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return -1;
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}
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return idx;
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Ebadf:
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printk("coda_read_super: Bad file\n");
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return -1;
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}
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static int coda_fill_super(struct super_block *sb, void *data, int silent)
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{
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struct inode *root = NULL;
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struct venus_comm *vc;
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struct CodaFid fid;
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int error;
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int idx;
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if (task_active_pid_ns(current) != &init_pid_ns)
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return -EINVAL;
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idx = get_device_index((struct coda_mount_data *) data);
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/* Ignore errors in data, for backward compatibility */
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if(idx == -1)
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idx = 0;
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printk(KERN_INFO "coda_read_super: device index: %i\n", idx);
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vc = &coda_comms[idx];
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mutex_lock(&vc->vc_mutex);
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if (!vc->vc_inuse) {
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printk("coda_read_super: No pseudo device\n");
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error = -EINVAL;
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goto unlock_out;
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}
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if (vc->vc_sb) {
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printk("coda_read_super: Device already mounted\n");
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error = -EBUSY;
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goto unlock_out;
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}
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error = bdi_setup_and_register(&vc->bdi, "coda", BDI_CAP_MAP_COPY);
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if (error)
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goto unlock_out;
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vc->vc_sb = sb;
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mutex_unlock(&vc->vc_mutex);
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sb->s_fs_info = vc;
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sb->s_flags |= MS_NOATIME;
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sb->s_blocksize = 4096; /* XXXXX what do we put here?? */
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sb->s_blocksize_bits = 12;
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sb->s_magic = CODA_SUPER_MAGIC;
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sb->s_op = &coda_super_operations;
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sb->s_d_op = &coda_dentry_operations;
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sb->s_bdi = &vc->bdi;
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/* get root fid from Venus: this needs the root inode */
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error = venus_rootfid(sb, &fid);
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if ( error ) {
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printk("coda_read_super: coda_get_rootfid failed with %d\n",
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error);
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goto error;
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}
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printk("coda_read_super: rootfid is %s\n", coda_f2s(&fid));
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/* make root inode */
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root = coda_cnode_make(&fid, sb);
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if (IS_ERR(root)) {
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error = PTR_ERR(root);
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printk("Failure of coda_cnode_make for root: error %d\n", error);
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goto error;
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}
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printk("coda_read_super: rootinode is %ld dev %s\n",
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root->i_ino, root->i_sb->s_id);
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sb->s_root = d_make_root(root);
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if (!sb->s_root) {
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error = -EINVAL;
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goto error;
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}
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return 0;
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error:
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mutex_lock(&vc->vc_mutex);
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bdi_destroy(&vc->bdi);
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vc->vc_sb = NULL;
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sb->s_fs_info = NULL;
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unlock_out:
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mutex_unlock(&vc->vc_mutex);
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return error;
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}
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static void coda_put_super(struct super_block *sb)
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{
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struct venus_comm *vcp = coda_vcp(sb);
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mutex_lock(&vcp->vc_mutex);
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bdi_destroy(&vcp->bdi);
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vcp->vc_sb = NULL;
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sb->s_fs_info = NULL;
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mutex_unlock(&vcp->vc_mutex);
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printk("Coda: Bye bye.\n");
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}
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static void coda_evict_inode(struct inode *inode)
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{
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truncate_inode_pages(&inode->i_data, 0);
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clear_inode(inode);
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coda_cache_clear_inode(inode);
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}
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int coda_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
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{
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int err = coda_revalidate_inode(dentry);
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if (!err)
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generic_fillattr(dentry->d_inode, stat);
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return err;
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}
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int coda_setattr(struct dentry *de, struct iattr *iattr)
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{
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struct inode *inode = de->d_inode;
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struct coda_vattr vattr;
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int error;
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memset(&vattr, 0, sizeof(vattr));
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inode->i_ctime = CURRENT_TIME_SEC;
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coda_iattr_to_vattr(iattr, &vattr);
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vattr.va_type = C_VNON; /* cannot set type */
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/* Venus is responsible for truncating the container-file!!! */
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error = venus_setattr(inode->i_sb, coda_i2f(inode), &vattr);
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if (!error) {
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coda_vattr_to_iattr(inode, &vattr);
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coda_cache_clear_inode(inode);
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}
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return error;
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}
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const struct inode_operations coda_file_inode_operations = {
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.permission = coda_permission,
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.getattr = coda_getattr,
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.setattr = coda_setattr,
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};
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static int coda_statfs(struct dentry *dentry, struct kstatfs *buf)
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{
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int error;
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error = venus_statfs(dentry, buf);
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if (error) {
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/* fake something like AFS does */
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buf->f_blocks = 9000000;
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buf->f_bfree = 9000000;
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buf->f_bavail = 9000000;
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buf->f_files = 9000000;
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buf->f_ffree = 9000000;
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}
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/* and fill in the rest */
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buf->f_type = CODA_SUPER_MAGIC;
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buf->f_bsize = 4096;
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buf->f_namelen = CODA_MAXNAMLEN;
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return 0;
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}
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/* init_coda: used by filesystems.c to register coda */
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static struct dentry *coda_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, coda_fill_super);
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}
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struct file_system_type coda_fs_type = {
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.owner = THIS_MODULE,
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.name = "coda",
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.mount = coda_mount,
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.kill_sb = kill_anon_super,
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.fs_flags = FS_BINARY_MOUNTDATA,
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};
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MODULE_ALIAS_FS("coda");
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