From: Eric Biggers <ebiggers@kernel.org>
To: linux-fscrypt@vger.kernel.org
Cc: linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH] fscrypt: don't evict dirty inodes after removing key
Date: Thu, 5 Mar 2020 00:41:38 -0800 [thread overview]
Message-ID: <20200305084138.653498-1-ebiggers@kernel.org> (raw)
From: Eric Biggers <ebiggers@google.com>
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+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/crypto/keysetup.c | 9 +++++++++
1 file changed, 9 insertions(+)
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
@@ -538,6 +538,15 @@ int fscrypt_drop_inode(struct inode *inode)
return 0;
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* immediately become outdated.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
--
2.25.1
next reply other threads:[~2020-03-05 8:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-05 8:41 Eric Biggers [this message]
2020-03-11 2:50 ` [PATCH] fscrypt: don't evict dirty inodes after removing key Eric Biggers
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