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Subject[PATCH 5.4 084/123] fscrypt: dont evict dirty inodes after removing key
Date
From: Eric Biggers <ebiggers@google.com>

commit 2b4eae95c7361e0a147b838715c8baa1380a428f upstream.

After FS_IOC_REMOVE_ENCRYPTION_KEY removes a key, it syncs the
filesystem and tries to get and put all inodes that were unlocked by the
key so that unused inodes get evicted via fscrypt_drop_inode().
Normally, the inodes are all clean due to the sync.

However, after the filesystem is sync'ed, userspace can modify and close
one of the files. (Userspace is *supposed* to close the files before
removing the key. But it doesn't always happen, and the kernel can't
assume it.) This causes the inode to be dirtied and have i_count == 0.
Then, fscrypt_drop_inode() failed to consider this case and indicated
that the inode can be dropped, causing the write to be lost.

On f2fs, other problems such as a filesystem freeze could occur due to
the inode being freed while still on f2fs's dirty inode list.

Fix this bug by making fscrypt_drop_inode() only drop clean inodes.

I've written an xfstest which detects this bug on ext4, f2fs, and ubifs.

Fixes: b1c0ec3599f4 ("fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl")
Cc: <stable@vger.kernel.org> # v5.4+
Link: https://lore.kernel.org/r/20200305084138.653498-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/crypto/keysetup.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -579,6 +579,15 @@ int fscrypt_drop_inode(struct inode *ino
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* immediately become outdated.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

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