[PATCH] ext4: require encryption feature for EXT4_IOC_SET_ENCRYPTION_POLICY

[Eric Biggers <ebiggers3@gmail.com>]

From: Richard Weinberger <richard@nod.at>

commit 9a200d075e5d05be1fcad4547a0f8aee4e2f9a04 upstream.  Please apply
to 4.4-stable.  (Having to make this change is unfortunate since it
could break some users of ext4 encryption, but we haven't received any
complaints about this being in the 4.9 kernel, and we need to do this
because otherwise anyone who can write to an ext4 filesystem with
block_size != PAGE_SIZE can crash the kernel or corrupt the filesystem.)

...otherwise an user can enable encryption for certain files even
when the filesystem is unable to support it.
Such a case would be a filesystem created by mkfs.ext4's default
settings, 1KiB block size. Ext4 supports encyption only when block size
is equal to PAGE_SIZE.
But this constraint is only checked when the encryption feature flag
is set.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/ext4/ioctl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 789e2d6724a9..bcd7c4788903 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -622,6 +622,9 @@ resizefs_out:
 		struct ext4_encryption_policy policy;
 		int err = 0;
 
+		if (!ext4_has_feature_encrypt(sb))
+			return -EOPNOTSUPP;
+
 		if (copy_from_user(&policy,
 				   (struct ext4_encryption_policy __user *)arg,
 				   sizeof(policy))) {
-- 
2.13.0.rc1.294.g07d810a77f-goog