/*
 *
 * Copyright (C) 2011 Novell Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/splice.h>
#include <linux/xattr.h>
#include <linux/security.h>
#include <linux/uaccess.h>
#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/fdtable.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"

#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)

static bool __read_mostly ovl_check_copy_up;
module_param_named(check_copy_up, ovl_check_copy_up, bool,
                   S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(ovl_check_copy_up,
                 "Warn on copy-up when causing process also has a R/O fd open");

static int ovl_check_fd(const void *data, struct file *f, unsigned int fd)
{
        const struct dentry *dentry = data;

        if (f->f_inode == d_inode(dentry))
                pr_warn_ratelimited("overlayfs: Warning: Copying up %pD, but open R/O on fd %u which will cease to be coherent [pid=%d %s]\n",
                                    f, fd, current->pid, current->comm);
        return 0;
}

/*
 * Check the fds open by this process and warn if something like the following
 * scenario is about to occur:
 *
 *      fd1 = open("foo", O_RDONLY);
 *      fd2 = open("foo", O_RDWR);
 */
static void ovl_do_check_copy_up(struct dentry *dentry)
{
        if (ovl_check_copy_up)
                iterate_fd(current->files, 0, ovl_check_fd, dentry);
}

int ovl_copy_xattr(struct dentry *old, struct dentry *new)
{
        ssize_t list_size, size, value_size = 0;
        char *buf, *name, *value = NULL;
        int uninitialized_var(error);

        if (!old->d_inode->i_op->getxattr ||
            !new->d_inode->i_op->getxattr)
                return 0;

        list_size = vfs_listxattr(old, NULL, 0);
        if (list_size <= 0) {
                if (list_size == -EOPNOTSUPP)
                        return 0;
                return list_size;
        }

        buf = kzalloc(list_size, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        list_size = vfs_listxattr(old, buf, list_size);
        if (list_size <= 0) {
                error = list_size;
                goto out;
        }

        for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
retry:
                size = vfs_getxattr(old, name, value, value_size);
                if (size == -ERANGE)
                        size = vfs_getxattr(old, name, NULL, 0);

                if (size < 0) {
                        error = size;
                        break;
                }

                if (size > value_size) {
                        void *new;

                        new = krealloc(value, size, GFP_KERNEL);
                        if (!new) {
                                error = -ENOMEM;
                                break;
                        }
                        value = new;
                        value_size = size;
                        goto retry;
                }

                error = vfs_setxattr(new, name, value, size, 0);
                if (error)
                        break;
        }
        kfree(value);
out:
        kfree(buf);
        return error;
}

static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
{
        struct file *old_file;
        struct file *new_file;
        loff_t old_pos = 0;
        loff_t new_pos = 0;
        int error = 0;

        if (len == 0)
                return 0;

        old_file = ovl_path_open(old, O_LARGEFILE | O_RDONLY);
        if (IS_ERR(old_file))
                return PTR_ERR(old_file);

        new_file = ovl_path_open(new, O_LARGEFILE | O_WRONLY);
        if (IS_ERR(new_file)) {
                error = PTR_ERR(new_file);
                goto out_fput;
        }

        /* FIXME: copy up sparse files efficiently */
        while (len) {
                size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
                long bytes;

                if (len < this_len)
                        this_len = len;

                if (signal_pending_state(TASK_KILLABLE, current)) {
                        error = -EINTR;
                        break;
                }

                bytes = do_splice_direct(old_file, &old_pos,
                                         new_file, &new_pos,
                                         this_len, SPLICE_F_MOVE);
                if (bytes <= 0) {
                        error = bytes;
                        break;
                }
                WARN_ON(old_pos != new_pos);

                len -= bytes;
        }

        fput(new_file);
out_fput:
        fput(old_file);
        return error;
}

static char *ovl_read_symlink(struct dentry *realdentry)
{
        int res;
        char *buf;
        struct inode *inode = realdentry->d_inode;
        mm_segment_t old_fs;

        res = -EINVAL;
        if (!inode->i_op->readlink)
                goto err;

        res = -ENOMEM;
        buf = (char *) __get_free_page(GFP_KERNEL);
        if (!buf)
                goto err;

        old_fs = get_fs();
        set_fs(get_ds());
        /* The cast to a user pointer is valid due to the set_fs() */
        res = inode->i_op->readlink(realdentry,
                                    (char __user *)buf, PAGE_SIZE - 1);
        set_fs(old_fs);
        if (res < 0) {
                free_page((unsigned long) buf);
                goto err;
        }
        buf[res] = '\0';

        return buf;

err:
        return ERR_PTR(res);
}

static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
{
        struct iattr attr = {
                .ia_valid =
                     ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
                .ia_atime = stat->atime,
                .ia_mtime = stat->mtime,
        };

        return notify_change(upperdentry, &attr, NULL);
}

int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
{
        int err = 0;

        if (!S_ISLNK(stat->mode)) {
                struct iattr attr = {
                        .ia_valid = ATTR_MODE,
                        .ia_mode = stat->mode,
                };
                err = notify_change(upperdentry, &attr, NULL);
        }
        if (!err) {
                struct iattr attr = {
                        .ia_valid = ATTR_UID | ATTR_GID,
                        .ia_uid = stat->uid,
                        .ia_gid = stat->gid,
                };
                err = notify_change(upperdentry, &attr, NULL);
        }
        if (!err)
                ovl_set_timestamps(upperdentry, stat);

        return err;
}

static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
                              struct dentry *dentry, struct path *lowerpath,
                              struct kstat *stat, const char *link)
{
        struct inode *wdir = workdir->d_inode;
        struct inode *udir = upperdir->d_inode;
        struct dentry *newdentry = NULL;
        struct dentry *upper = NULL;
        umode_t mode = stat->mode;
        int err;

        newdentry = ovl_lookup_temp(workdir, dentry);
        err = PTR_ERR(newdentry);
        if (IS_ERR(newdentry))
                goto out;

        upper = lookup_one_len(dentry->d_name.name, upperdir,
                               dentry->d_name.len);
        err = PTR_ERR(upper);
        if (IS_ERR(upper))
                goto out1;

        /* Can't properly set mode on creation because of the umask */
        stat->mode &= S_IFMT;
        err = ovl_create_real(wdir, newdentry, stat, link, NULL, true);
        stat->mode = mode;
        if (err)
                goto out2;

        if (S_ISREG(stat->mode)) {
                struct path upperpath;

                ovl_path_upper(dentry, &upperpath);
                BUG_ON(upperpath.dentry != NULL);
                upperpath.dentry = newdentry;

                err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
                if (err)
                        goto out_cleanup;
        }

        err = ovl_copy_xattr(lowerpath->dentry, newdentry);
        if (err)
                goto out_cleanup;

        inode_lock(newdentry->d_inode);
        err = ovl_set_attr(newdentry, stat);
        inode_unlock(newdentry->d_inode);
        if (err)
                goto out_cleanup;

        err = ovl_do_rename(wdir, newdentry, udir, upper, 0);
        if (err)
                goto out_cleanup;

        ovl_dentry_update(dentry, newdentry);
        newdentry = NULL;

        /*
         * Non-directores become opaque when copied up.
         */
        if (!S_ISDIR(stat->mode))
                ovl_dentry_set_opaque(dentry, true);
out2:
        dput(upper);
out1:
        dput(newdentry);
out:
        return err;

out_cleanup:
        ovl_cleanup(wdir, newdentry);
        goto out2;
}

/*
 * Copy up a single dentry
 *
 * Directory renames only allowed on "pure upper" (already created on
 * upper filesystem, never copied up).  Directories which are on lower or
 * are merged may not be renamed.  For these -EXDEV is returned and
 * userspace has to deal with it.  This means, when copying up a
 * directory we can rely on it and ancestors being stable.
 *
 * Non-directory renames start with copy up of source if necessary.  The
 * actual rename will only proceed once the copy up was successful.  Copy
 * up uses upper parent i_mutex for exclusion.  Since rename can change
 * d_parent it is possible that the copy up will lock the old parent.  At
 * that point the file will have already been copied up anyway.
 */
int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
                    struct path *lowerpath, struct kstat *stat)
{
        struct dentry *workdir = ovl_workdir(dentry);
        int err;
        struct kstat pstat;
        struct path parentpath;
        struct dentry *upperdir;
        struct dentry *upperdentry;
        const struct cred *old_cred;
        struct cred *override_cred;
        char *link = NULL;

        if (WARN_ON(!workdir))
                return -EROFS;

        ovl_do_check_copy_up(lowerpath->dentry);

        ovl_path_upper(parent, &parentpath);
        upperdir = parentpath.dentry;

        err = vfs_getattr(&parentpath, &pstat);
        if (err)
                return err;

        if (S_ISLNK(stat->mode)) {
                link = ovl_read_symlink(lowerpath->dentry);
                if (IS_ERR(link))
                        return PTR_ERR(link);
        }

        err = -ENOMEM;
        override_cred = prepare_creds();
        if (!override_cred)
                goto out_free_link;

        override_cred->fsuid = stat->uid;
        override_cred->fsgid = stat->gid;
        /*
         * CAP_SYS_ADMIN for copying up extended attributes
         * CAP_DAC_OVERRIDE for create
         * CAP_FOWNER for chmod, timestamp update
         * CAP_FSETID for chmod
         * CAP_CHOWN for chown
         * CAP_MKNOD for mknod
         */
        cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
        cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
        cap_raise(override_cred->cap_effective, CAP_FOWNER);
        cap_raise(override_cred->cap_effective, CAP_FSETID);
        cap_raise(override_cred->cap_effective, CAP_CHOWN);
        cap_raise(override_cred->cap_effective, CAP_MKNOD);
        old_cred = override_creds(override_cred);

        err = -EIO;
        if (lock_rename(workdir, upperdir) != NULL) {
                pr_err("overlayfs: failed to lock workdir+upperdir\n");
                goto out_unlock;
        }
        upperdentry = ovl_dentry_upper(dentry);
        if (upperdentry) {
                /* Raced with another copy-up?  Nothing to do, then... */
                err = 0;
                goto out_unlock;
        }

        err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
                                 stat, link);
        if (!err) {
                /* Restore timestamps on parent (best effort) */
                ovl_set_timestamps(upperdir, &pstat);
        }
out_unlock:
        unlock_rename(workdir, upperdir);
        revert_creds(old_cred);
        put_cred(override_cred);

out_free_link:
        if (link)
                free_page((unsigned long) link);

        return err;
}

int ovl_copy_up(struct dentry *dentry)
{
        int err;

        err = 0;
        while (!err) {
                struct dentry *next;
                struct dentry *parent;
                struct path lowerpath;
                struct kstat stat;
                enum ovl_path_type type = ovl_path_type(dentry);

                if (OVL_TYPE_UPPER(type))
                        break;

                next = dget(dentry);
                /* find the topmost dentry not yet copied up */
                for (;;) {
                        parent = dget_parent(next);

                        type = ovl_path_type(parent);
                        if (OVL_TYPE_UPPER(type))
                                break;

                        dput(next);
                        next = parent;
                }

                ovl_path_lower(next, &lowerpath);
                err = vfs_getattr(&lowerpath, &stat);
                if (!err)
                        err = ovl_copy_up_one(parent, next, &lowerpath, &stat);

                dput(parent);
                dput(next);
        }

        return err;
}