[v7,3/3] btrfs: Add unprivileged version of ino_lookup ioctl
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Message ID e2e544650821449ec68925abc355dedc0d4836be.1526863497.git.misono.tomohiro@jp.fujitsu.com
State New
Headers show

Commit Message

Misono Tomohiro May 21, 2018, 1:09 a.m. UTC
Add unprivileged version of ino_lookup ioctl BTRFS_IOC_INO_LOOKUP_USER
to allow normal users to call "btrfs subvolume list/show" etc. in
combination with BTRFS_IOC_GET_SUBVOL_INFO/BTRFS_IOC_GET_SUBVOL_ROOTREF.

This can be used like BTRFS_IOC_INO_LOOKUP but the argument is
different. This is  because it always searches the fs/file tree
correspoinding to the fd with which this ioctl is called and also
returns the name of bottom subvolume.

The main differences from original ino_lookup ioctl are:
  1. Read + Exec 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 256 (BTRFS_VOL_NAME_MAX+1)
bytes than ino_lookup ioctl because of space of subvolume's name.

Reviewed-by: Gu Jinxiang <gujx@cn.fujitsu.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Tested-by: Gu Jinxiang <gujx@cn.fujitsu.com>
Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/ioctl.c           | 204 +++++++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/btrfs.h |  17 ++++
 2 files changed, 221 insertions(+)

Patch
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diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 66237e83f54d..7e0ea42813da 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2345,6 +2345,166 @@  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 inode *inode,
+				struct btrfs_ioctl_ino_lookup_user_args *args)
+{
+	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+	struct super_block *sb = inode->i_sb;
+	struct btrfs_key upper_limit = BTRFS_I(inode)->location;
+	u64 treeid = BTRFS_I(inode)->root->root_key.objectid;
+	u64 dirid = args->dirid;
+
+	unsigned long item_off;
+	unsigned long item_len;
+	struct btrfs_inode_ref *iref;
+	struct btrfs_root_ref *rref;
+	struct btrfs_root *root;
+	struct btrfs_path *path;
+	struct btrfs_key key, key2;
+	struct extent_buffer *l;
+	struct inode *temp_inode;
+	char *ptr;
+	int slot;
+	int len;
+	int total_len = 0;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/*
+	 * If the bottom subvolume does not exist directly under upper_limit,
+	 * construct the path in bottomup way.
+	 */
+	if (dirid != upper_limit.objectid) {
+		ptr = &args->path[BTRFS_INO_LOOKUP_USER_PATH_MAX - 1];
+
+		key.objectid = treeid;
+		key.type = BTRFS_ROOT_ITEM_KEY;
+		key.offset = (u64)-1;
+		root = btrfs_read_fs_root_no_name(fs_info, &key);
+		if (IS_ERR(root)) {
+			ret = PTR_ERR(root);
+			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+exec permission of this directory */
+			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);
+			if (key2.objectid != dirid) {
+				ret = -ENOENT;
+				goto out;
+			}
+
+			temp_inode = btrfs_iget(sb, &key2, root, NULL);
+			ret = inode_permission(temp_inode, MAY_READ | MAY_EXEC);
+			iput(temp_inode);
+			if (ret) {
+				ret = -EACCES;
+				goto out;
+			}
+
+			if (key.offset == upper_limit.objectid)
+				break;
+			if (key.objectid == BTRFS_FIRST_FREE_OBJECTID) {
+				ret = -EACCES;
+				goto out;
+			}
+
+			btrfs_release_path(path);
+			key.objectid = key.offset;
+			key.offset = (u64)-1;
+			dirid = key.objectid;
+		}
+
+		memmove(args->path, ptr, total_len);
+		args->path[total_len] = '\0';
+		btrfs_release_path(path);
+	}
+
+	/* get the bottom subvolume's name from ROOT_REF */
+	root = fs_info->tree_root;
+	key.objectid = treeid;
+	key.type = BTRFS_ROOT_REF_KEY;
+	key.offset = args->subvolid;
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	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);
+
+	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 dirid */
+	rref = btrfs_item_ptr(l, slot, struct btrfs_root_ref);
+	if (args->dirid != btrfs_root_ref_dirid(l, rref)) {
+		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;
+}
+
 static noinline int btrfs_ioctl_ino_lookup(struct file *file,
 					   void __user *argp)
 {
@@ -2387,6 +2547,48 @@  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 + Exec 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;
+
+	args = memdup_user(argp, sizeof(*args));
+	if (IS_ERR(args))
+		return PTR_ERR(args);
+
+	inode = file_inode(file);
+
+	if (args->dirid == BTRFS_FIRST_FREE_OBJECTID &&
+	    BTRFS_I(inode)->location.objectid != BTRFS_FIRST_FREE_OBJECTID) {
+	/* The subvolume does not exist under fd with which this is called */
+		kfree(args);
+		return -EACCES;
+	}
+
+	ret = btrfs_search_path_in_tree_user(inode, args);
+
+	if (ret == 0 && copy_to_user(argp, args, sizeof(*args)))
+		ret = -EFAULT;
+
+	kfree(args);
+	return ret;
+}
+
 /* Get the subvolume information in BTRFS_ROOT_ITEM and BTRFS_ROOT_BACKREF */
 static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
 					   void __user *argp)
@@ -5772,6 +5974,8 @@  long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_get_subvol_info(file, argp);
 	case BTRFS_IOC_GET_SUBVOL_ROOTREF:
 		return btrfs_ioctl_get_subvol_rootref(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 b6633f5d4847..177447c4d4c6 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -422,6 +422,21 @@  struct btrfs_ioctl_ino_lookup_args {
 	char name[BTRFS_INO_LOOKUP_PATH_MAX];
 };
 
+#define BTRFS_INO_LOOKUP_USER_PATH_MAX (4080-BTRFS_VOL_NAME_MAX-1)
+struct btrfs_ioctl_ino_lookup_user_args {
+	/* in, inode number containing the subvolume of 'subvolid' */
+	__u64 dirid;
+	/* in */
+	__u64 subvolid;
+	/* out, name of the subvolume of 'subvolid' */
+	char name[BTRFS_VOL_NAME_MAX + 1];
+	/*
+	 * out, constructed path from the directory with which
+	 * the ioctl is called to dirid
+	 */
+	char path[BTRFS_INO_LOOKUP_USER_PATH_MAX];
+};
+
 /* Search criteria for the btrfs SEARCH ioctl family. */
 struct btrfs_ioctl_search_key {
 	/*
@@ -910,5 +925,7 @@  enum btrfs_err_code {
 				struct btrfs_ioctl_get_subvol_info_args)
 #define BTRFS_IOC_GET_SUBVOL_ROOTREF _IOWR(BTRFS_IOCTL_MAGIC, 61, \
 				struct btrfs_ioctl_get_subvol_rootref_args)
+#define BTRFS_IOC_INO_LOOKUP_USER _IOWR(BTRFS_IOCTL_MAGIC, 62, \
+				struct btrfs_ioctl_ino_lookup_user_args)
 
 #endif /* _UAPI_LINUX_BTRFS_H */