On 6.03.2018 10:30, Misono, Tomohiro wrote:
> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
> from root tree. The arguments of this ioctl are the same as treesearch
> ioctl and can be used like treesearch ioctl.
>
> Since treesearch ioctl requires root privilege, this ioctl is needed
> to allow normal users to call "btrfs subvolume list/show" etc.
>
> Note that the subvolume name in ROOT_BACKREF/ROOT_REF will not be copied to
> prevent potential name leak. The name can be obtained by calling
> user version's ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER).
>
> Signed-off-by: Tomohiro Misono <misono.tomohiro@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/ioctl.c | 254 +++++++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/btrfs.h | 2 +
> 2 files changed, 256 insertions(+)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 111ee282b777..1dba309dce31 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1921,6 +1921,28 @@ static noinline int key_in_sk(struct btrfs_key *key,
> return 1;
> }
>
> +/*
> + * check if key is in sk and subvolume related range
> + */
> +static noinline int key_in_sk_and_subvol(struct btrfs_key *key,
> + struct btrfs_ioctl_search_key *sk)
> +{
> + int ret;
> +
> + ret = key_in_sk(key, sk);
> + if (!ret)
> + return 0;
> +
> + if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
> + (key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
> + key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
Why do you need the FIRST_FREE/LAST_FREE object id checks? The range
described by those are ordinary files. Since you are only interested in
subvolume data then you should omit those, no?
> + key->type >= BTRFS_ROOT_ITEM_KEY &&
> + key->type <= BTRFS_ROOT_BACKREF_KEY)
I think this check should really be:
if (key->objectid == BTRFS_FS_TREE_OBJECTID || key->objectid ==
BTRFS_ROOT_ITEM_KEY || key->type == BTRFS_ROOT_BACKREF_KEY
> + return 1;
> +
> + return 0;
> +}
> +
> static noinline int copy_to_sk(struct btrfs_path *path,
> struct btrfs_key *key,
> struct btrfs_ioctl_search_key *sk,
> @@ -2045,6 +2067,142 @@ static noinline int copy_to_sk(struct btrfs_path *path,
> return ret;
> }
>
> +/*
> + * Basically the same as copy_to_sk() but restricts the copied item
> + * within subvolume related one using key_in_sk_and_subvol().
> + * Also, the name of subvolume will be omitted from
> + * ROOT_BACKREF/ROOT_REF item.
> + */
> +static noinline int copy_subvol_item(struct btrfs_path *path,
> + struct btrfs_key *key,
> + struct btrfs_ioctl_search_key *sk,
> + size_t *buf_size,
> + char __user *ubuf,
> + unsigned long *sk_offset,
> + int *num_found)
> +{
> + u64 found_transid;
> + struct extent_buffer *leaf;
> + struct btrfs_ioctl_search_header sh;
> + struct btrfs_key test;
> + unsigned long item_off;
> + unsigned long item_len;
> + int nritems;
> + int i;
> + int slot;
> + int ret = 0;
> +
> + leaf = path->nodes[0];
> + slot = path->slots[0];
> + nritems = btrfs_header_nritems(leaf);
> +
> + if (btrfs_header_generation(leaf) > sk->max_transid) {
> + i = nritems;
> + goto advance_key;
I don't see why you need a goto label at all. Just put the necessary
code inside the if and return directly.
> + }
> + found_transid = btrfs_header_generation(leaf);
> +
> + for (i = slot; i < nritems; i++) {
> + item_off = btrfs_item_ptr_offset(leaf, i);
> + item_len = btrfs_item_size_nr(leaf, i);
> +
> + btrfs_item_key_to_cpu(leaf, key, i);
> + if (!key_in_sk_and_subvol(key, sk))
> + continue;
> +
> + /* will not copy the name of subvolume */
> + if (key->type == BTRFS_ROOT_BACKREF_KEY ||
> + key->type == BTRFS_ROOT_REF_KEY)
> + item_len = sizeof(struct btrfs_root_ref);
> +
> + if (sizeof(sh) + item_len > *buf_size) {
> + if (*num_found) {
> + ret = 1;
> + goto out;
This can be a simple return 1;
> + }
> +
> + /*
> + * return one empty item back for v1, which does not
> + * handle -EOVERFLOW
> + */
> +
> + *buf_size = sizeof(sh) + item_len;
> + item_len = 0;
> + ret = -EOVERFLOW;
> + }
> +
> + if (sizeof(sh) + item_len + *sk_offset > *buf_size) {
> + ret = 1;
> + goto out;
ditto
> + }
> +
> + sh.objectid = key->objectid;
> + sh.offset = key->offset;
> + sh.type = key->type;
> + sh.len = item_len;
> + sh.transid = found_transid;
> +
> + /* copy search result header */
> + if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
> + ret = -EFAULT;
> + goto out;
ditto
> + }
> +
> + *sk_offset += sizeof(sh);
> +
> + if (item_len) {
> + char __user *up = ubuf + *sk_offset;
> +
> + /* copy the item */
> + if (read_extent_buffer_to_user(leaf, up,
> + item_off, item_len)) {
> + ret = -EFAULT;
> + goto out;
ditto
> + }
> +
> + *sk_offset += item_len;
> + }
> + (*num_found)++;
> +
> + if (ret) /* -EOVERFLOW from above */
> + goto out;
return ret
> +
> + if (*num_found >= sk->nr_items) {
> + ret = 1;
> + goto out;
return 1
> + }
> + }
> +advance_key:
> + ret = 0;
> + test.objectid = sk->max_objectid;
> + test.type = sk->max_type;
> + test.offset = sk->max_offset;
> + if (btrfs_comp_cpu_keys(key, &test) >= 0)
> + ret = 1;
> + else if (key->offset < (u64)-1)
> + key->offset++;
> + else if (key->type < (u8)-1) {
> + key->offset = 0;
> + key->type++;
> + } else if (key->objectid < (u64)-1) {
> + key->offset = 0;
> + key->type = 0;
> + key->objectid++;
> + } else
> + ret = 1;
> +out:
Given that you are not doing any unwinding of locks or some such I don't
see any reason for the label at all.
> + /*
> + * 0: all items from this leaf copied, continue with next
> + * 1: * more items can be copied, but unused buffer is too small
> + * * all items were found
> + * Either way, it will stops the loop which iterates to the next
> + * leaf
> + * -EOVERFLOW: item was to large for buffer
> + * -EFAULT: could not copy extent buffer back to userspace
> + */
Put the description of the return value above the function definition
> + return ret;
> +}
> +
> static noinline int search_ioctl(struct inode *inode,
> struct btrfs_ioctl_search_key *sk,
> size_t *buf_size,
> @@ -2309,6 +2467,100 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
> return ret;
> }
>
> +static noinline int search_subvol(struct inode *inode,
> + struct btrfs_ioctl_search_key *sk,
> + size_t *buf_size,
> + char __user *ubuf)
> +{
> + struct btrfs_fs_info *info = btrfs_sb(inode->i_sb);
> + struct btrfs_root *root;
> + struct btrfs_key key;
> + struct btrfs_path *path;
> + unsigned long sk_offset = 0;
> + int num_found = 0;
> + int ret;
> +
> + path = btrfs_alloc_path();
> + if (!path)
> + return -ENOMEM;
> +
> + /* search ROOT TREEE */
> + 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)) {
> + btrfs_free_path(path);
> + return -ENOENT;
> + }
So why do you have to do this, when you can just do :
struct btrfs_root *root = fs_info->tree_root;
Looking at the wider codebase, the root tree is referenced directly
almost all the time. btrfs_read_fs_root_no_name is generally used when
you have the objectid of a particular subvol root item and you want to
get that one. But this is not the case here.
> +
> + key.objectid = sk->min_objectid;
> + key.type = sk->min_type;
> + key.offset = sk->min_offset;
> +
> + while (1) {
> + ret = btrfs_search_forward(root, &key, path, sk->min_transid);
> + if (ret != 0) {
> + if (ret > 0)
> + ret = 0;
> + goto err;
> + }
> +
> + ret = copy_subvol_item(path, &key, sk, buf_size, ubuf,
> + &sk_offset, &num_found);
> + btrfs_release_path(path);
> + if (ret)
> + break;
> + }
> +
> + if (ret > 0)
> + ret = 0;
> +err:
> + sk->nr_items = num_found;
> + btrfs_free_path(path);
> + return ret;
> +}
> +
> +/*
> + * Unprivileged ioctl for getting subvolume related item.
> + * The arguments are the same as btrfs_ioctl_tree_search()
> + * and can be used like tree search ioctl.
> + *
> + * Only returns ROOT_ITEM/ROOT_BACKREF/ROOT_REF key of subvolumes
> + * from root tree. Also, the name of subvolume will be omitted from
> + * ROOT_BACKREF/ROOT_REF item to prevent name leak.
> + */
> +static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
> + void __user *argp)
> +{
> + struct btrfs_ioctl_search_args __user *uargs;
> + struct btrfs_ioctl_search_key sk;
> + struct inode *inode;
> + size_t buf_size;
> + int ret;
> +
> + uargs = (struct btrfs_ioctl_search_args __user *)argp;
> +
> + if (copy_from_user(&sk, &uargs->key, sizeof(sk)))
> + return -EFAULT;
> +
> + buf_size = sizeof(uargs->buf);
> +
> + inode = file_inode(file);
> + ret = search_subvol(inode, &sk, &buf_size, uargs->buf);
> +
> + /*
> + * In the original implementation an overflow is handled by returning a
> + * search header with a len of zero, so reset ret.
> + */
> + if (ret == -EOVERFLOW)
> + ret = 0;
> +
> + if (ret == 0 && copy_to_user(&uargs->key, &sk, sizeof(sk)))
> + ret = -EFAULT;
> + return ret;
> +}
> +
> static noinline int btrfs_ioctl_snap_destroy(struct file *file,
> void __user *arg)
> {
> @@ -5663,6 +5915,8 @@ long btrfs_ioctl(struct file *file, unsigned int
> return btrfs_ioctl_get_features(file, argp);
> case BTRFS_IOC_SET_FEATURES:
> return btrfs_ioctl_set_features(file, argp);
> + case BTRFS_IOC_GET_SUBVOL_INFO:
> + return btrfs_ioctl_get_subvol_info(file, argp);
> }
>
> return -ENOTTY;
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index c8d99b9ca550..1e9361cf66d5 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -843,5 +843,7 @@ enum btrfs_err_code {
> struct btrfs_ioctl_vol_args_v2)
> #define BTRFS_IOC_LOGICAL_INO_V2 _IOWR(BTRFS_IOCTL_MAGIC, 59, \
> struct btrfs_ioctl_logical_ino_args)
> +#define BTRFS_IOC_GET_SUBVOL_INFO _IOWR(BTRFS_IOCTL_MAGIC, 60, \
> + struct btrfs_ioctl_search_args)
>
> #endif /* _UAPI_LINUX_BTRFS_H */
>
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