Merge tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt

Pull fscrypt fix from Eric Biggers:
 "Fix a bug where if userspace is writing to encrypted files while the
  FS_IOC_REMOVE_ENCRYPTION_KEY ioctl (introduced in v5.4) is running,
  dirty inodes could be evicted, causing writes could be lost or the
  filesystem to hang due to a use-after-free. This was encountered
  during real-world use, not just theoretical.

  Tested with the existing fscrypt xfstests, and with a new xfstest I
  wrote to reproduce this bug. This fix does expose an existing bug with
  '-o lazytime' that Ted is working on fixing, but this fix is more
  critical and needed anyway regardless of the lazytime fix"

* tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt:
  fscrypt: don't evict dirty inodes after removing key

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 65cb09fa6ead..08c9f216a54d 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -539,6 +539,15 @@ int fscrypt_drop_inode(struct inode *inode)
 	mk = ci->ci_master_key->payload.data[0];
 
 	/*
+	 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
+	 * protected by the key were cleaned by sync_filesystem().  But if
+	 * userspace is still using the files, inodes can be dirtied between
+	 * then and now.  We mustn't lose any writes, so skip dirty inodes here.
+	 */
+	if (inode->i_state & I_DIRTY_ALL)
+		return 0;
+
+	/*
 	 * Note: since we aren't holding ->mk_secret_sem, the result here can
 	 * immediately become outdated.  But there's no correctness problem with
 	 * unnecessarily evicting.  Nor is there a correctness problem with not