From: Eric Biggers <ebiggers@google.com>
Date: Thu, 8 Sep 2016 21:20:38 +0000 (-0700)
Subject: fscrypto: require write access to mount to set encryption policy
X-Git-Tag: v4.7.5~183
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=399c967d80f1dfc8273a3831d73a9f06daa4b1bc;p=thirdparty%2Fkernel%2Fstable.git

fscrypto: require write access to mount to set encryption policy

commit ba63f23d69a3a10e7e527a02702023da68ef8a6d upstream.

Since setting an encryption policy requires writing metadata to the
filesystem, it should be guarded by mnt_want_write/mnt_drop_write.
Otherwise, a user could cause a write to a frozen or readonly
filesystem.  This was handled correctly by f2fs but not by ext4.  Make
fscrypt_process_policy() handle it rather than relying on the filesystem
to get it right.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 28cc412852afb..64eddc5289eb8 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -782,7 +782,13 @@ resizefs_out:
 			goto encryption_policy_out;
 		}
 
+		err = mnt_want_write_file(filp);
+		if (err)
+			goto encryption_policy_out;
+
 		err = ext4_process_policy(&policy, inode);
+
+		mnt_drop_write_file(filp);
 encryption_policy_out:
 		return err;
 #else