ext4 crypto: use a jbd2 transaction when adding a crypto policy

Start a jbd2 transaction, and mark the inode dirty on the inode under
that transaction after setting the encrypt flag.  Otherwise if the
directory isn't modified after setting the crypto policy, the
encrypted flag might not survive the inode getting pushed out from
memory, or the the file system getting unmounted and remounted.
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/ext4/crypto_policy.c

@@ -12,6 +12,7 @@
 #include <linux/string.h>
 #include <linux/types.h>
 
+#include "ext4_jbd2.h"
 #include "ext4.h"
 #include "xattr.h"
 
@@ -49,7 +50,8 @@ static int ext4_create_encryption_context_from_policy(
 	struct inode *inode, const struct ext4_encryption_policy *policy)
 {
 	struct ext4_encryption_context ctx;
-	int res = 0;
+	handle_t *handle;
+	int res, res2;
 
 	res = ext4_convert_inline_data(inode);
 	if (res)
@@ -78,11 +80,22 @@ static int ext4_create_encryption_context_from_policy(
 	BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
 	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
 
+	handle = ext4_journal_start(inode, EXT4_HT_MISC,
+				    ext4_jbd2_credits_xattr(inode));
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
 	res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 			     sizeof(ctx), 0);
-	if (!res)
+	if (!res) {
 		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
+		res = ext4_mark_inode_dirty(handle, inode);
+		if (res)
+			EXT4_ERROR_INODE(inode, "Failed to mark inode dirty");
+	}
+	res2 = ext4_journal_stop(handle);
+	if (!res)
+		res = res2;
 	return res;
 }