[PATCH] fscrypto: lock inode while setting encryption policy

[Eric Biggers <ebiggers3@gmail.com>]

From: Eric Biggers <ebiggers@google.com>

commit 8906a8223ad4909b391c5628f7991ebceda30e52 upstream.  Please apply
to 4.4-stable; it is already in 4.9-stable.  This is a backport of the
fix to fs/ext4/ and fs/f2fs/ for old kernels.

i_rwsem needs to be acquired while setting an encryption policy so that
concurrent calls to FS_IOC_SET_ENCRYPTION_POLICY are correctly
serialized (especially the ->get_context() + ->set_context() pair), and
so that new files cannot be created in the directory during or after the
->empty_dir() check.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Richard Weinberger <richard@nod.at>
Cc: stable@vger.kernel.org
---
 fs/ext4/ioctl.c | 4 ++++
 fs/f2fs/file.c  | 9 ++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 1fb12f9c97a6..789e2d6724a9 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -633,8 +633,12 @@ resizefs_out:
 		if (err)
 			goto encryption_policy_out;
 
+		mutex_lock(&inode->i_mutex);
+
 		err = ext4_process_policy(&policy, inode);
 
+		mutex_unlock(&inode->i_mutex);
+
 		mnt_drop_write_file(filp);
 encryption_policy_out:
 		return err;
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index a197215ad52b..4b449d263333 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1535,12 +1535,19 @@ static int f2fs_ioc_set_encryption_policy(struct file *filp, unsigned long arg)
 #ifdef CONFIG_F2FS_FS_ENCRYPTION
 	struct f2fs_encryption_policy policy;
 	struct inode *inode = file_inode(filp);
+	int err;
 
 	if (copy_from_user(&policy, (struct f2fs_encryption_policy __user *)arg,
 				sizeof(policy)))
 		return -EFAULT;
 
-	return f2fs_process_policy(&policy, inode);
+	mutex_lock(&inode->i_mutex);
+
+	err = f2fs_process_policy(&policy, inode);
+
+	mutex_unlock(&inode->i_mutex);
+
+	return err;
 #else
 	return -EOPNOTSUPP;
 #endif
-- 
2.12.0.367.g23dc2f6d3c-goog