diff options
Diffstat (limited to 'fs/overlayfs/copy_up.c')
-rw-r--r-- | fs/overlayfs/copy_up.c | 385 |
1 files changed, 385 insertions, 0 deletions
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c new file mode 100644 index 00000000000..87dbeee0a14 --- /dev/null +++ b/fs/overlayfs/copy_up.c @@ -0,0 +1,385 @@ +/* + * + * 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/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 "overlayfs.h" + +#define OVL_COPY_UP_CHUNK_SIZE (1 << 20) + +static int ovl_copy_up_xattr(struct dentry *old, struct dentry *new) +{ + ssize_t list_size, size; + char *buf, *name, *value; + int 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; + + error = -ENOMEM; + value = kmalloc(XATTR_SIZE_MAX, GFP_KERNEL); + if (!value) + goto out; + + list_size = vfs_listxattr(old, buf, list_size); + if (list_size <= 0) { + error = list_size; + goto out_free_value; + } + + for (name = buf; name < (buf + list_size); name += strlen(name) + 1) { + size = vfs_getxattr(old, name, value, XATTR_SIZE_MAX); + if (size <= 0) { + error = size; + goto out_free_value; + } + error = vfs_setxattr(new, name, value, size, 0); + if (error) + goto out_free_value; + } + +out_free_value: + 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; + int error = 0; + + if (len == 0) + return 0; + + old_file = ovl_path_open(old, O_RDONLY); + if (IS_ERR(old_file)) + return PTR_ERR(old_file); + + new_file = ovl_path_open(new, O_WRONLY); + if (IS_ERR(new_file)) { + error = PTR_ERR(new_file); + goto out_fput; + } + + /* FIXME: copy up sparse files efficiently */ + while (len) { + loff_t offset = new_file->f_pos; + 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, &offset, new_file, this_len, + SPLICE_F_MOVE); + if (bytes <= 0) { + error = bytes; + break; + } + + 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); +} + +static int ovl_set_mode(struct dentry *upperdentry, umode_t mode) +{ + struct iattr attr = { + .ia_valid = ATTR_MODE, + .ia_mode = mode, + }; + + return notify_change(upperdentry, &attr); +} + +static int ovl_copy_up_locked(struct dentry *upperdir, struct dentry *dentry, + struct path *lowerpath, struct kstat *stat, + const char *link) +{ + int err; + struct path newpath; + umode_t mode = stat->mode; + + /* Can't properly set mode on creation because of the umask */ + stat->mode &= S_IFMT; + + ovl_path_upper(dentry, &newpath); + WARN_ON(newpath.dentry); + newpath.dentry = ovl_upper_create(upperdir, dentry, stat, link); + if (IS_ERR(newpath.dentry)) + return PTR_ERR(newpath.dentry); + + if (S_ISREG(stat->mode)) { + err = ovl_copy_up_data(lowerpath, &newpath, stat->size); + if (err) + goto err_remove; + } + + err = ovl_copy_up_xattr(lowerpath->dentry, newpath.dentry); + if (err) + goto err_remove; + + mutex_lock(&newpath.dentry->d_inode->i_mutex); + if (!S_ISLNK(stat->mode)) + err = ovl_set_mode(newpath.dentry, mode); + if (!err) + err = ovl_set_timestamps(newpath.dentry, stat); + mutex_unlock(&newpath.dentry->d_inode->i_mutex); + if (err) + goto err_remove; + + ovl_dentry_update(dentry, newpath.dentry); + + /* + * Easiest way to get rid of the lower dentry reference is to + * drop this dentry. This is neither needed nor possible for + * directories. + */ + if (!S_ISDIR(stat->mode)) + d_drop(dentry); + + return 0; + +err_remove: + if (S_ISDIR(stat->mode)) + vfs_rmdir(upperdir->d_inode, newpath.dentry); + else + vfs_unlink(upperdir->d_inode, newpath.dentry); + + dput(newpath.dentry); + + return err; +} + +/* + * 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. + */ +static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry, + struct path *lowerpath, struct kstat *stat) +{ + int err; + struct kstat pstat; + struct path parentpath; + struct dentry *upperdir; + const struct cred *old_cred; + struct cred *override_cred; + char *link = NULL; + + ovl_path_upper(parent, &parentpath); + upperdir = parentpath.dentry; + + err = vfs_getattr(parentpath.mnt, parentpath.dentry, &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_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_MKNOD); + old_cred = override_creds(override_cred); + + mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT); + if (ovl_path_type(dentry) != OVL_PATH_LOWER) { + err = 0; + } else { + err = ovl_copy_up_locked(upperdir, dentry, lowerpath, + stat, link); + if (!err) { + /* Restore timestamps on parent (best effort) */ + ovl_set_timestamps(upperdir, &pstat); + } + } + + mutex_unlock(&upperdir->d_inode->i_mutex); + + 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 (type != OVL_PATH_LOWER) + break; + + next = dget(dentry); + /* find the topmost dentry not yet copied up */ + for (;;) { + parent = dget_parent(next); + + type = ovl_path_type(parent); + if (type != OVL_PATH_LOWER) + break; + + dput(next); + next = parent; + } + + ovl_path_lower(next, &lowerpath); + err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat); + if (!err) + err = ovl_copy_up_one(parent, next, &lowerpath, &stat); + + dput(parent); + dput(next); + } + + return err; +} + +/* Optimize by not copying up the file first and truncating later */ +int ovl_copy_up_truncate(struct dentry *dentry, loff_t size) +{ + int err; + struct kstat stat; + struct path lowerpath; + struct dentry *parent = dget_parent(dentry); + + err = ovl_copy_up(parent); + if (err) + goto out_dput_parent; + + ovl_path_lower(dentry, &lowerpath); + err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat); + if (err) + goto out_dput_parent; + + if (size < stat.size) + stat.size = size; + + err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat); + +out_dput_parent: + dput(parent); + return err; +} |