[PATCH 3.2 136/152] btrfs: ensure that file descriptor used with subvol ioctls is a dir

[Ben Hutchings]

3.2.84-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Mahoney <jeffm@xxxxxxxx>

commit 325c50e3cebb9208009083e841550f98a863bfa0 upstream.

If the subvol/snapshot create/destroy ioctls are passed a regular file
with execute permissions set, we'll eventually Oops while trying to do
inode->i_op->lookup via lookup_one_len.

This patch ensures that the file descriptor refers to a directory.

Fixes: cb8e70901d (Btrfs: Fix subvolume creation locking rules)
Fixes: 76dda93c6a (Btrfs: add snapshot/subvolume destroy ioctl)
Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
[bwh: Backported to 3.2:
 - Open-code file_inode()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/btrfs/ioctl.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1302,6 +1302,9 @@ static noinline int btrfs_ioctl_snap_cre
 	int namelen;
 	int ret = 0;
 
+	if (!S_ISDIR(file->f_dentry->d_inode->i_mode))
+		return -ENOTDIR;
+
 	if (root->fs_info->sb->s_flags & MS_RDONLY)
 		return -EROFS;
 
@@ -1350,6 +1353,9 @@ static noinline int btrfs_ioctl_snap_cre
 	struct btrfs_ioctl_vol_args *vol_args;
 	int ret;
 
+	if (!S_ISDIR(file->f_dentry->d_inode->i_mode))
+		return -ENOTDIR;
+
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args))
 		return PTR_ERR(vol_args);
@@ -1372,6 +1378,9 @@ static noinline int btrfs_ioctl_snap_cre
 	u64 *ptr = NULL;
 	bool readonly = false;
 
+	if (!S_ISDIR(file->f_dentry->d_inode->i_mode))
+		return -ENOTDIR;
+
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args))
 		return PTR_ERR(vol_args);
@@ -1848,6 +1857,9 @@ static noinline int btrfs_ioctl_snap_des
 	int ret;
 	int err = 0;
 
+	if (!S_ISDIR(dir->i_mode))
+		return -ENOTDIR;
+
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args))
 		return PTR_ERR(vol_args);