On 2018/03/06 17:31, Misono, Tomohiro wrote:
> Add unprivileged version of ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER)
> to allow normal users to call "btrfs subvololume list/show" etc. in
> combination with BTRFS_IOC_GET_SUBVOL_INFO.
>
> This can be used like BTRFS_IOC_INO_LOOKUP but the argument is
> different because it also returns the name of bottom subvolume,
> which is ommited by BTRFS_IOC_GET_SUBVOL_INFO ioctl.
> Also, this must be called with fd which exists under the tree of
> args->treeid to prevent for user to search any tree.
>
> The main differences from original ino_lookup ioctl are:
> 1. Read permission will be checked using inode_permission()
> during path construction. -EACCES will be returned in case
> of failure.
> 2. Path construction will be stopped at the inode number which
> corresponds to the fd with which this ioctl is called. If
> constructed path does not exist under fd's inode, -EACCES
> will be returned.
> 3. The name of bottom subvolume is also searched and filled.
>
> Note that the maximum length of path is shorter 272 bytes than
> ino_lookup ioctl because of space of subvolume's id and name.
>
> Signed-off-by: Tomohiro Misono <misono.tomohiro@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/ioctl.c | 218 +++++++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/btrfs.h | 16 ++++
> 2 files changed, 234 insertions(+)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 1dba309dce31..ac23da98b7e7 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2425,6 +2425,179 @@ static noinline int btrfs_search_path_in_tree(struct btrfs_fs_info *info,
> return ret;
> }
>
> +static noinline int btrfs_search_path_in_tree_user(struct btrfs_fs_info *info,
> + struct super_block *sb,
> + struct btrfs_key upper_limit,
> + struct btrfs_ioctl_ino_lookup_user_args *args)
> +{
> + struct btrfs_root *root;
> + struct btrfs_key key, key2;
> + char *ptr;
> + int ret = -1;
> + int slot;
> + int len;
> + int total_len = 0;
> + u64 dirid = args->dirid;
> + struct btrfs_inode_ref *iref;
> + struct btrfs_root_ref rref;
> +
> + unsigned long item_off;
> + unsigned long item_len;
> +
> + struct extent_buffer *l;
> + struct btrfs_path *path = NULL;
> +
> + struct inode *inode;
> + int *new = 0;
> +
> + path = btrfs_alloc_path();
> + if (!path)
> + return -ENOMEM;
> +
> + if (dirid == upper_limit.objectid)
> + /*
> + * If the bottom subvolume exists directly under upper limit,
> + * there is no need to construct the path and just get the
> + * subvolume's name
> + */
> + goto get_subvol_name;
> + if (dirid == BTRFS_FIRST_FREE_OBJECTID)
> + /* The subvolume does not exist under upper_limit */
> + goto access_err;
> +
> + ptr = &args->path[BTRFS_INO_LOOKUP_PATH_MAX - 1];
> +
> + key.objectid = args->treeid;
> + key.type = BTRFS_ROOT_ITEM_KEY;
> + key.offset = (u64)-1;
> + root = btrfs_read_fs_root_no_name(info, &key);
> + if (IS_ERR(root)) {
> + btrfs_err(info, "could not find root %llu", args->treeid);
> + ret = -ENOENT;
> + goto out;
> + }
> +
> + key.objectid = dirid;
> + key.type = BTRFS_INODE_REF_KEY;
> + key.offset = (u64)-1;
> +
> + while (1) {
> + ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> + if (ret < 0)
> + goto out;
> + else if (ret > 0) {
> + ret = btrfs_previous_item(root, path, dirid,
> + BTRFS_INODE_REF_KEY);
> + if (ret < 0)
> + goto out;
> + else if (ret > 0) {
> + ret = -ENOENT;
> + goto out;
> + }
> + }
> +
> + l = path->nodes[0];
> + slot = path->slots[0];
> + btrfs_item_key_to_cpu(l, &key, slot);
> +
> + iref = btrfs_item_ptr(l, slot, struct btrfs_inode_ref);
> + len = btrfs_inode_ref_name_len(l, iref);
> + ptr -= len + 1;
> + total_len += len + 1;
> + if (ptr < args->path) {
> + ret = -ENAMETOOLONG;
> + goto out;
> + }
> +
> + *(ptr + len) = '/';
> + read_extent_buffer(l, ptr, (unsigned long)(iref + 1), len);
> +
> + /* Check the read permission */
> + ret = btrfs_previous_item(root, path, dirid,
> + BTRFS_INODE_ITEM_KEY);
> + if (ret < 0) {
> + goto out;
> + } else if (ret > 0) {
> + ret = -ENOENT;
> + goto out;
> + }
> + l = path->nodes[0];
> + slot = path->slots[0];
> +
> + btrfs_item_key_to_cpu(l, &key2, slot);
> + inode = btrfs_iget(sb, &key2, root, new);
> + ret = inode_permission(inode, MAY_READ);
> + iput(inode);
> + if (ret)
> + goto access_err;
> +
> + if (key.offset == BTRFS_FIRST_FREE_OBJECTID ||
> + key.offset == upper_limit.objectid)
> + break;
> +
> + btrfs_release_path(path);
> + key.objectid = key.offset;
> + key.offset = (u64)-1;
> + dirid = key.objectid;
> + }
> + /* Check if the searched path exists under the upper_limit */
> + if (key.offset == BTRFS_FIRST_FREE_OBJECTID &&
> + upper_limit.objectid != BTRFS_FIRST_FREE_OBJECTID)
> + goto access_err;
> +
> + memmove(args->path, ptr, total_len);
> + args->path[total_len] = '\0';
> + btrfs_release_path(path);
> + ret = 0;
> +
> +get_subvol_name:
> + /* Get subolume's name from ROOT_REF */
> + key.objectid = BTRFS_ROOT_TREE_OBJECTID;
> + key.type = BTRFS_ROOT_ITEM_KEY;
> + key.offset = (u64)-1;
> + root = btrfs_read_fs_root_no_name(info, &key);
> + if (IS_ERR(root)) {
> + ret = -ENOENT;
> + goto out;
> + }
> +
> + key.objectid = args->treeid;
> + key.type = BTRFS_ROOT_REF_KEY;
> + key.offset = args->subid;
> + ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> + if (ret != 0) {
> + ret = -ENOENT;
> + goto out;
> + }
> + l = path->nodes[0];
> + slot = path->slots[0];
> + btrfs_item_key_to_cpu(l, &key, slot);
> +
> + item_off = btrfs_item_ptr_offset(l, slot);
> + item_len = btrfs_item_size_nr(l, slot);
> + /* Check if dirid in ROOT_REF corresponds to passed arg */
> + read_extent_buffer(l, &rref, item_off, sizeof(struct btrfs_root_ref));
> + if (rref.dirid != args->dirid) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + /* Copy subvolume's name */
> + item_off += sizeof(struct btrfs_root_ref);
> + item_len -= sizeof(struct btrfs_root_ref);
> + read_extent_buffer(l, args->name, item_off, item_len);
> + args->name[item_len] = '\0';
> +
> +out:
> + btrfs_free_path(path);
> + return ret;
> +
> +access_err:
> + btrfs_free_path(path);
> + ret = -EACCES;
> + return ret;
> +}
> +
> static noinline int btrfs_ioctl_ino_lookup(struct file *file,
> void __user *argp)
> {
> @@ -2467,6 +2640,49 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
> return ret;
> }
>
> +/*
> + * User version of ino_lookup ioctl (unprivileged)
> + *
> + * The main differences from original ino_lookup ioctl are:
> + * 1. Read permission will be checked using inode_permission()
> + * during path construction. -EACCES will be returned in case
> + * of failure.
> + * 2. Path construction will be stopped at the inode number which
> + * corresponds to the fd with which this ioctl is called. If
> + * constructed path does not exist under fd's inode, -EACCES
> + * will be returned.
> + * 3. The name of bottom subvolume is also searched and filled.
> + */
> +static noinline int btrfs_ioctl_ino_lookup_user(struct file *file,
> + void __user *argp)
> +{
> + struct btrfs_ioctl_ino_lookup_user_args *args;
> + struct inode *inode;
> + int ret = 0;
> +
> + args = memdup_user(argp, sizeof(*args));
> + if (IS_ERR(args))
> + return PTR_ERR(args);
> +
> + inode = file_inode(file);
> + /*
> + * args->treeid must be matched with this inode's objectid
> + * to previent for user to search any fs/file tree.
> + */
> + if (args->treeid != BTRFS_I(inode)->root->root_key.objectid)
> + return -EINVAL;
> +
> + ret = btrfs_search_path_in_tree_user(BTRFS_I(inode)->root->fs_info,
> + inode->i_sb, BTRFS_I(inode)->location,
> + args);
> +
> + if (ret == 0 && copy_to_user(argp, args, sizeof(*args)))
> + ret = -EFAULT;
> +
> + kfree(args);
> + return ret;
> +}
> +
> static noinline int search_subvol(struct inode *inode,
> struct btrfs_ioctl_search_key *sk,
> size_t *buf_size,
> @@ -5917,6 +6133,8 @@ long btrfs_ioctl(struct file *file, unsigned int
> return btrfs_ioctl_set_features(file, argp);
> case BTRFS_IOC_GET_SUBVOL_INFO:
> return btrfs_ioctl_get_subvol_info(file, argp);
> + case BTRFS_IOC_INO_LOOKUP_USER:
> + return btrfs_ioctl_ino_lookup_user(file, argp);
> }
>
> return -ENOTTY;
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index 1e9361cf66d5..22326d631417 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -422,6 +422,20 @@ struct btrfs_ioctl_ino_lookup_args {
> char name[BTRFS_INO_LOOKUP_PATH_MAX];
> };
>
> +#define BTRFS_INO_LOOKUP_USER_PATH_MAX (4072-BTRFS_VOL_NAME_MAX)
> +struct btrfs_ioctl_ino_lookup_user_args {
> + /* in */
> + __u64 treeid;
> + /* in, 'dirid' is the same as objectid in btrfs_ioctl_ino_lookup_args */
> + __u64 dirid;
> + /* in, subvolume id which exists under the directory of 'dirid' */
> + __u64 subid;
> + /* out, name of the subvolume of 'subid' */
> + char name[BTRFS_VOL_NAME_MAX];
> + /* out, 'path' is the same as 'name' in btrfs_ioctl_ino_lookup_args */
> + char path[BTRFS_INO_LOOKUP_USER_PATH_MAX];
> +};
> +
> /* Search criteria for the btrfs SEARCH ioctl family. */
> struct btrfs_ioctl_search_key {
> /*
> @@ -845,5 +859,7 @@ enum btrfs_err_code {
> struct btrfs_ioctl_logical_ino_args)
> #define BTRFS_IOC_GET_SUBVOL_INFO _IOWR(BTRFS_IOCTL_MAGIC, 60, \
> struct btrfs_ioctl_search_args)
> +#define BTRFS_IOC_INO_LOOKUP_USER _IOWR(BTRFS_IOCTL_MAGIC, 61, \
> + struct btrfs_ioctl_ino_lookup_args)
The argument obviously should be "btrfs_ioctl_ino_lookup_user_args".
I will fix this in v2.
>
> #endif /* _UAPI_LINUX_BTRFS_H */
>
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