procfs: preparations for remove_proc_entry() race fixes

[deliverable/linux.git] / fs / proc / inode.c

/*
 *  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/printk.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;
        void *ns;

        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;
        ns = PROC_I(inode)->ns;
        if (ns_ops && ns)
                ns_ops->put(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,
};

enum {BIAS = -1U<<31};

static inline int use_pde(struct proc_dir_entry *pde)
{
        int res = 1;
        spin_lock(&pde->pde_unload_lock);
        if (unlikely(pde->pde_users < 0))
                res = 0;
        else
                pde->pde_users++;
        spin_unlock(&pde->pde_unload_lock);
        return res;
}

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

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

void proc_entry_rundown(struct proc_dir_entry *de)
{
        spin_lock(&de->pde_unload_lock);
        de->pde_users += BIAS;
        /* Wait until all existing callers into module are done. */
        if (de->pde_users != BIAS) {
                DECLARE_COMPLETION_ONSTACK(c);
                de->pde_unload_completion = &c;
                spin_unlock(&de->pde_unload_lock);

                wait_for_completion(de->pde_unload_completion);

                spin_lock(&de->pde_unload_lock);
        }

        while (!list_empty(&de->pde_openers)) {
                struct pde_opener *pdeo;
                struct file *file;

                pdeo = list_first_entry(&de->pde_openers, struct pde_opener, lh);
                list_del(&pdeo->lh);
                spin_unlock(&de->pde_unload_lock);
                file = pdeo->file;
                de->proc_fops->release(file_inode(file), file);
                kfree(pdeo);
                spin_lock(&de->pde_unload_lock);
        }
        spin_unlock(&de->pde_unload_lock);
}

/* ->read_proc() users - legacy crap */
static ssize_t
proc_file_read(struct file *file, char __user *buf, size_t nbytes,
               loff_t *ppos)
{
        struct proc_dir_entry *pde = PDE(file_inode(file));
        ssize_t rv = -EIO;
        if (use_pde(pde)) {
                rv = __proc_file_read(file, buf, nbytes, ppos);
                unuse_pde(pde);
        }
        return rv;
}

static loff_t
proc_file_lseek(struct file *file, loff_t offset, int orig)
{
        loff_t retval = -EINVAL;
        switch (orig) {
        case 1:
                offset += file->f_pos;
        /* fallthrough */
        case 0:
                if (offset < 0 || offset > MAX_NON_LFS)
                        break;
                file->f_pos = retval = offset;
        }
        return retval;
}

const struct file_operations proc_file_operations = {
        .llseek         = proc_file_lseek,
        .read           = proc_file_read,
};

static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
{
        struct proc_dir_entry *pde = PDE(file_inode(file));
        loff_t rv = -EINVAL;
        if (use_pde(pde)) {
                loff_t (*llseek)(struct file *, loff_t, int);
                llseek = pde->proc_fops->llseek;
                if (!llseek)
                        llseek = default_llseek;
                rv = llseek(file, offset, whence);
                unuse_pde(pde);
        }
        return rv;
}

static ssize_t proc_reg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
        ssize_t (*read)(struct file *, char __user *, size_t, loff_t *);
        struct proc_dir_entry *pde = PDE(file_inode(file));
        ssize_t rv = -EIO;
        if (use_pde(pde)) {
                read = pde->proc_fops->read;
                if (read)
                        rv = read(file, buf, count, ppos);
                unuse_pde(pde);
        }
        return rv;
}

static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
        ssize_t (*write)(struct file *, const char __user *, size_t, loff_t *);
        struct proc_dir_entry *pde = PDE(file_inode(file));
        ssize_t rv = -EIO;
        if (use_pde(pde)) {
                write = pde->proc_fops->write;
                if (write)
                        rv = write(file, buf, count, ppos);
                unuse_pde(pde);
        }
        return rv;
}

static unsigned int proc_reg_poll(struct file *file, struct poll_table_struct *pts)
{
        struct proc_dir_entry *pde = PDE(file_inode(file));
        unsigned int rv = DEFAULT_POLLMASK;
        unsigned int (*poll)(struct file *, struct poll_table_struct *);
        if (use_pde(pde)) {
                poll = pde->proc_fops->poll;
                if (poll)
                        rv = poll(file, pts);
                unuse_pde(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_inode(file));
        long rv = -ENOTTY;
        long (*ioctl)(struct file *, unsigned int, unsigned long);
        if (use_pde(pde)) {
                ioctl = pde->proc_fops->unlocked_ioctl;
                if (ioctl)
                        rv = ioctl(file, cmd, arg);
                unuse_pde(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_inode(file));
        long rv = -ENOTTY;
        long (*compat_ioctl)(struct file *, unsigned int, unsigned long);
        if (use_pde(pde)) {
                compat_ioctl = pde->proc_fops->compat_ioctl;
                if (compat_ioctl)
                        rv = compat_ioctl(file, cmd, arg);
                unuse_pde(pde);
        }
        return rv;
}
#endif

static int proc_reg_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct proc_dir_entry *pde = PDE(file_inode(file));
        int rv = -EIO;
        int (*mmap)(struct file *, struct vm_area_struct *);
        if (use_pde(pde)) {
                mmap = pde->proc_fops->mmap;
                if (mmap)
                        rv = mmap(file, vma);
                unuse_pde(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;

        if (!use_pde(pde)) {
                kfree(pdeo);
                return -ENOENT;
        }
        open = pde->proc_fops->open;
        release = pde->proc_fops->release;

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

        spin_lock(&pde->pde_unload_lock);
        if (rv == 0 && release) {
                /* To know what to release. */
                pdeo->file = file;
                /* Strictly for "too late" ->release in proc_reg_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 file *file)
{
        struct pde_opener *pdeo;

        list_for_each_entry(pdeo, &pde->pde_openers, lh) {
                if (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, file);
        if (pde->pde_users < 0) {
                /*
                 * 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 = pde->proc_fops->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);

        unuse_pde(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 = new_inode_pseudo(sb);

        if (inode) {
                inode->i_ino = de->low_ino;
                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);
                WARN_ON(!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;
                        }
                }
        } else
               pde_put(de);
        return inode;
}

int proc_fill_super(struct super_block *s)
{
        struct inode *root_inode;

        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);
        root_inode = proc_get_inode(s, &proc_root);
        if (!root_inode) {
                pr_err("proc_fill_super: get root inode failed\n");
                return -ENOMEM;
        }

        s->s_root = d_make_root(root_inode);
        if (!s->s_root) {
                pr_err("proc_fill_super: allocate dentry failed\n");
                return -ENOMEM;
        }

        return proc_setup_self(s);
}