inode.c

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/*
 *  linux/fs/proc/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/kernel.h>
#include <linux/pid_namespace.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/completion.h>
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/limits.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/mount.h>

#include <asm/uaccess.h>

#include "internal.h"

static void proc_evict_inode(struct inode *inode)
{
    struct proc_dir_entry *de;
    struct ctl_table_header *head;
    const struct proc_ns_operations *ns_ops;

    truncate_inode_pages(&inode->i_data, 0);
    clear_inode(inode);

    /* Stop tracking associated processes */
    put_pid(PROC_I(inode)->pid);

    /* Let go of any associated proc directory entry */
    de = PROC_I(inode)->pde;
    if (de)
        pde_put(de);
    head = PROC_I(inode)->sysctl;
    if (head) {
        rcu_assign_pointer(PROC_I(inode)->sysctl, NULL);
        sysctl_head_put(head);
    }
    /* Release any associated namespace */
    ns_ops = PROC_I(inode)->ns_ops;
    if (ns_ops && ns_ops->put)
        ns_ops->put(PROC_I(inode)->ns);
}

static struct kmem_cache * proc_inode_cachep;

static struct inode *proc_alloc_inode(struct super_block *sb)
{
    struct proc_inode *ei;
    struct inode *inode;

    ei = (struct proc_inode *)kmem_cache_alloc(proc_inode_cachep, GFP_KERNEL);
    if (!ei)
        return NULL;
    ei->pid = NULL;
    ei->fd = 0;
    ei->op.proc_get_link = NULL;
    ei->pde = NULL;
    ei->sysctl = NULL;
    ei->sysctl_entry = NULL;
    ei->ns = NULL;
    ei->ns_ops = NULL;
    inode = &ei->vfs_inode;
    inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
    return inode;
}

static void proc_i_callback(struct rcu_head *head)
{
    struct inode *inode = container_of(head, struct inode, i_rcu);
    kmem_cache_free(proc_inode_cachep, PROC_I(inode));
}

static void proc_destroy_inode(struct inode *inode)
{
    call_rcu(&inode->i_rcu, proc_i_callback);
}

static void init_once(void *foo)
{
    struct proc_inode *ei = (struct proc_inode *) foo;

    inode_init_once(&ei->vfs_inode);
}

void __init proc_init_inodecache(void)
{
    proc_inode_cachep = kmem_cache_create("proc_inode_cache",
                         sizeof(struct proc_inode),
                         0, (SLAB_RECLAIM_ACCOUNT|
                        SLAB_MEM_SPREAD|SLAB_PANIC),
                         init_once);
}

static int proc_show_options(struct seq_file *seq, struct dentry *root)
{
    struct super_block *sb = root->d_sb;
    struct pid_namespace *pid = sb->s_fs_info;

    if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
        seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));
    if (pid->hide_pid != 0)
        seq_printf(seq, ",hidepid=%u", pid->hide_pid);

    return 0;
}

static const struct super_operations proc_sops = {
    .alloc_inode    = proc_alloc_inode,
    .destroy_inode  = proc_destroy_inode,
    .drop_inode = generic_delete_inode,
    .evict_inode    = proc_evict_inode,
    .statfs     = simple_statfs,
    .remount_fs = proc_remount,
    .show_options   = proc_show_options,
};

static void __pde_users_dec(struct proc_dir_entry *pde)
{
    pde->pde_users--;
    if (pde->pde_unload_completion && pde->pde_users == 0)
        complete(pde->pde_unload_completion);
}

void pde_users_dec(struct proc_dir_entry *pde)
{
    spin_lock(&pde->pde_unload_lock);
    __pde_users_dec(pde);
    spin_unlock(&pde->pde_unload_lock);
}

static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    loff_t rv = -EINVAL;
    loff_t (*llseek)(struct file *, loff_t, int);

    spin_lock(&pde->pde_unload_lock);
    /*
     * remove_proc_entry() is going to delete PDE (as part of module
     * cleanup sequence). No new callers into module allowed.
     */
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    /*
     * Bump refcount so that remove_proc_entry will wail for ->llseek to
     * complete.
     */
    pde->pde_users++;
    /*
     * Save function pointer under lock, to protect against ->proc_fops
     * NULL'ifying right after ->pde_unload_lock is dropped.
     */
    llseek = pde->proc_fops->llseek;
    spin_unlock(&pde->pde_unload_lock);

    if (!llseek)
        llseek = default_llseek;
    rv = llseek(file, offset, whence);

    pde_users_dec(pde);
    return rv;
}

static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    ssize_t rv = -EIO;
    ssize_t (*read)(struct file *, char __user *, size_t, loff_t *);

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    read = pde->proc_fops->read;
    spin_unlock(&pde->pde_unload_lock);

    if (read)
        rv = read(file, buf, count, ppos);

    pde_users_dec(pde);
    return rv;
}

static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    ssize_t rv = -EIO;
    ssize_t (*write)(struct file *, const char __user *, size_t, loff_t *);

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    write = pde->proc_fops->write;
    spin_unlock(&pde->pde_unload_lock);

    if (write)
        rv = write(file, buf, count, ppos);

    pde_users_dec(pde);
    return rv;
}

static unsigned int proc_reg_poll(struct file *file, struct poll_table_struct *pts)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    unsigned int rv = DEFAULT_POLLMASK;
    unsigned int (*poll)(struct file *, struct poll_table_struct *);

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    poll = pde->proc_fops->poll;
    spin_unlock(&pde->pde_unload_lock);

    if (poll)
        rv = poll(file, pts);

    pde_users_dec(pde);
    return rv;
}

static long proc_reg_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    long rv = -ENOTTY;
    long (*ioctl)(struct file *, unsigned int, unsigned long);

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    ioctl = pde->proc_fops->unlocked_ioctl;
    spin_unlock(&pde->pde_unload_lock);

    if (ioctl)
        rv = ioctl(file, cmd, arg);

    pde_users_dec(pde);
    return rv;
}

#ifdef CONFIG_COMPAT
static long proc_reg_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    long rv = -ENOTTY;
    long (*compat_ioctl)(struct file *, unsigned int, unsigned long);

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    compat_ioctl = pde->proc_fops->compat_ioctl;
    spin_unlock(&pde->pde_unload_lock);

    if (compat_ioctl)
        rv = compat_ioctl(file, cmd, arg);

    pde_users_dec(pde);
    return rv;
}
#endif

static int proc_reg_mmap(struct file *file, struct vm_area_struct *vma)
{
    struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
    int rv = -EIO;
    int (*mmap)(struct file *, struct vm_area_struct *);

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    mmap = pde->proc_fops->mmap;
    spin_unlock(&pde->pde_unload_lock);

    if (mmap)
        rv = mmap(file, vma);

    pde_users_dec(pde);
    return rv;
}

static int proc_reg_open(struct inode *inode, struct file *file)
{
    struct proc_dir_entry *pde = PDE(inode);
    int rv = 0;
    int (*open)(struct inode *, struct file *);
    int (*release)(struct inode *, struct file *);
    struct pde_opener *pdeo;

    /*
     * What for, you ask? Well, we can have open, rmmod, remove_proc_entry
     * sequence. ->release won't be called because ->proc_fops will be
     * cleared. Depending on complexity of ->release, consequences vary.
     *
     * We can't wait for mercy when close will be done for real, it's
     * deadlockable: rmmod foo </proc/foo . So, we're going to do ->release
     * by hand in remove_proc_entry(). For this, save opener's credentials
     * for later.
     */
    pdeo = kmalloc(sizeof(struct pde_opener), GFP_KERNEL);
    if (!pdeo)
        return -ENOMEM;

    spin_lock(&pde->pde_unload_lock);
    if (!pde->proc_fops) {
        spin_unlock(&pde->pde_unload_lock);
        kfree(pdeo);
        return -ENOENT;
    }
    pde->pde_users++;
    open = pde->proc_fops->open;
    release = pde->proc_fops->release;
    spin_unlock(&pde->pde_unload_lock);

    if (open)
        rv = open(inode, file);

    spin_lock(&pde->pde_unload_lock);
    if (rv == 0 && release) {
        /* To know what to release. */
        pdeo->inode = inode;
        pdeo->file = file;
        /* Strictly for "too late" ->release in proc_reg_release(). */
        pdeo->release = release;
        list_add(&pdeo->lh, &pde->pde_openers);
    } else
        kfree(pdeo);
    __pde_users_dec(pde);
    spin_unlock(&pde->pde_unload_lock);
    return rv;
}

static struct pde_opener *find_pde_opener(struct proc_dir_entry *pde,
                    struct inode *inode, struct file *file)
{
    struct pde_opener *pdeo;

    list_for_each_entry(pdeo, &pde->pde_openers, lh) {
        if (pdeo->inode == inode && pdeo->file == file)
            return pdeo;
    }
    return NULL;
}

static int proc_reg_release(struct inode *inode, struct file *file)
{
    struct proc_dir_entry *pde = PDE(inode);
    int rv = 0;
    int (*release)(struct inode *, struct file *);
    struct pde_opener *pdeo;

    spin_lock(&pde->pde_unload_lock);
    pdeo = find_pde_opener(pde, inode, file);
    if (!pde->proc_fops) {
        /*
         * Can't simply exit, __fput() will think that everything is OK,
         * and move on to freeing struct file. remove_proc_entry() will
         * find slacker in opener's list and will try to do non-trivial
         * things with struct file. Therefore, remove opener from list.
         *
         * But if opener is removed from list, who will ->release it?
         */
        if (pdeo) {
            list_del(&pdeo->lh);
            spin_unlock(&pde->pde_unload_lock);
            rv = pdeo->release(inode, file);
            kfree(pdeo);
        } else
            spin_unlock(&pde->pde_unload_lock);
        return rv;
    }
    pde->pde_users++;
    release = pde->proc_fops->release;
    if (pdeo) {
        list_del(&pdeo->lh);
        kfree(pdeo);
    }
    spin_unlock(&pde->pde_unload_lock);

    if (release)
        rv = release(inode, file);

    pde_users_dec(pde);
    return rv;
}

static const struct file_operations proc_reg_file_ops = {
    .llseek     = proc_reg_llseek,
    .read       = proc_reg_read,
    .write      = proc_reg_write,
    .poll       = proc_reg_poll,
    .unlocked_ioctl = proc_reg_unlocked_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = proc_reg_compat_ioctl,
#endif
    .mmap       = proc_reg_mmap,
    .open       = proc_reg_open,
    .release    = proc_reg_release,
};

#ifdef CONFIG_COMPAT
static const struct file_operations proc_reg_file_ops_no_compat = {
    .llseek     = proc_reg_llseek,
    .read       = proc_reg_read,
    .write      = proc_reg_write,
    .poll       = proc_reg_poll,
    .unlocked_ioctl = proc_reg_unlocked_ioctl,
    .mmap       = proc_reg_mmap,
    .open       = proc_reg_open,
    .release    = proc_reg_release,
};
#endif

struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
{
    struct inode * inode;

    inode = iget_locked(sb, de->low_ino);
    if (!inode)
        return NULL;
    if (inode->i_state & I_NEW) {
        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
        PROC_I(inode)->pde = de;

        if (de->mode) {
            inode->i_mode = de->mode;
            inode->i_uid = de->uid;
            inode->i_gid = de->gid;
        }
        if (de->size)
            inode->i_size = de->size;
        if (de->nlink)
            set_nlink(inode, de->nlink);
        if (de->proc_iops)
            inode->i_op = de->proc_iops;
        if (de->proc_fops) {
            if (S_ISREG(inode->i_mode)) {
#ifdef CONFIG_COMPAT
                if (!de->proc_fops->compat_ioctl)
                    inode->i_fop =
                        &proc_reg_file_ops_no_compat;
                else
#endif
                    inode->i_fop = &proc_reg_file_ops;
            } else {
                inode->i_fop = de->proc_fops;
            }
        }
        unlock_new_inode(inode);
    } else
           pde_put(de);
    return inode;
}           

int proc_fill_super(struct super_block *s)
{
    s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
    s->s_blocksize = 1024;
    s->s_blocksize_bits = 10;
    s->s_magic = PROC_SUPER_MAGIC;
    s->s_op = &proc_sops;
    s->s_time_gran = 1;
    
    pde_get(&proc_root);
    s->s_root = d_make_root(proc_get_inode(s, &proc_root));
    if (s->s_root)
        return 0;

    printk("proc_read_super: get root inode failed\n");
    pde_put(&proc_root);
    return -ENOMEM;
}