Patch "fscrypt: add fscrypt_is_nokey_name()" has been added to the 4.19-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

    fscrypt: add fscrypt_is_nokey_name()

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fscrypt-add-fscrypt_is_nokey_name.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From foo at baz Wed Dec 30 04:40:58 PM CET 2020
From: Eric Biggers <ebiggers at kernel.org>
Date: Mon, 28 Dec 2020 11:12:08 -0800
Subject: fscrypt: add fscrypt_is_nokey_name()
To: stable at vger.kernel.org
Cc: linux-fscrypt at vger.kernel.org, linux-ext4 at vger.kernel.org, linux-f2fs-devel at lists.sourceforge.net, linux-mtd at lists.infradead.org
Message-ID: <20201228191211.138300-2-ebiggers at kernel.org>

From: Eric Biggers <ebiggers at google.com>

commit 159e1de201b6fca10bfec50405a3b53a561096a8 upstream.

It's possible to create a duplicate filename in an encrypted directory
by creating a file concurrently with adding the encryption key.

Specifically, sys_open(O_CREAT) (or sys_mkdir(), sys_mknod(), or
sys_symlink()) can lookup the target filename while the directory's
encryption key hasn't been added yet, resulting in a negative no-key
dentry.  The VFS then calls ->create() (or ->mkdir(), ->mknod(), or
->symlink()) because the dentry is negative.  Normally, ->create() would
return -ENOKEY due to the directory's key being unavailable.  However,
if the key was added between the dentry lookup and ->create(), then the
filesystem will go ahead and try to create the file.

If the target filename happens to already exist as a normal name (not a
no-key name), a duplicate filename may be added to the directory.

In order to fix this, we need to fix the filesystems to prevent
->create(), ->mkdir(), ->mknod(), and ->symlink() on no-key names.
(->rename() and ->link() need it too, but those are already handled
correctly by fscrypt_prepare_rename() and fscrypt_prepare_link().)

In preparation for this, add a helper function fscrypt_is_nokey_name()
that filesystems can use to do this check.  Use this helper function for
the existing checks that fs/crypto/ does for rename and link.

Cc: stable at vger.kernel.org
Link: https://lore.kernel.org/r/20201118075609.120337-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers at google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 fs/crypto/hooks.c               |   10 +++++-----
 include/linux/fscrypt_notsupp.h |    5 +++++
 include/linux/fscrypt_supp.h    |   29 +++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 5 deletions(-)

--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -58,8 +58,8 @@ int __fscrypt_prepare_link(struct inode
 	if (err)
 		return err;
 
-	/* ... in case we looked up ciphertext name before key was added */
-	if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
+	/* ... in case we looked up no-key name before key was added */
+	if (fscrypt_is_nokey_name(dentry))
 		return -ENOKEY;
 
 	if (!fscrypt_has_permitted_context(dir, inode))
@@ -83,9 +83,9 @@ int __fscrypt_prepare_rename(struct inod
 	if (err)
 		return err;
 
-	/* ... in case we looked up ciphertext name(s) before key was added */
-	if ((old_dentry->d_flags | new_dentry->d_flags) &
-	    DCACHE_ENCRYPTED_NAME)
+	/* ... in case we looked up no-key name(s) before key was added */
+	if (fscrypt_is_nokey_name(old_dentry) ||
+	    fscrypt_is_nokey_name(new_dentry))
 		return -ENOKEY;
 
 	if (old_dir != new_dir) {
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -24,6 +24,11 @@ static inline bool fscrypt_dummy_context
 	return false;
 }
 
+static inline bool fscrypt_is_nokey_name(const struct dentry *dentry)
+{
+	return false;
+}
+
 /* crypto.c */
 static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work)
 {
--- a/include/linux/fscrypt_supp.h
+++ b/include/linux/fscrypt_supp.h
@@ -58,6 +58,35 @@ static inline bool fscrypt_dummy_context
 		inode->i_sb->s_cop->dummy_context(inode);
 }
 
+/**
+ * fscrypt_is_nokey_name() - test whether a dentry is a no-key name
+ * @dentry: the dentry to check
+ *
+ * This returns true if the dentry is a no-key dentry.  A no-key dentry is a
+ * dentry that was created in an encrypted directory that hasn't had its
+ * encryption key added yet.  Such dentries may be either positive or negative.
+ *
+ * When a filesystem is asked to create a new filename in an encrypted directory
+ * and the new filename's dentry is a no-key dentry, it must fail the operation
+ * with ENOKEY.  This includes ->create(), ->mkdir(), ->mknod(), ->symlink(),
+ * ->rename(), and ->link().  (However, ->rename() and ->link() are already
+ * handled by fscrypt_prepare_rename() and fscrypt_prepare_link().)
+ *
+ * This is necessary because creating a filename requires the directory's
+ * encryption key, but just checking for the key on the directory inode during
+ * the final filesystem operation doesn't guarantee that the key was available
+ * during the preceding dentry lookup.  And the key must have already been
+ * available during the dentry lookup in order for it to have been checked
+ * whether the filename already exists in the directory and for the new file's
+ * dentry not to be invalidated due to it incorrectly having the no-key flag.
+ *
+ * Return: %true if the dentry is a no-key name
+ */
+static inline bool fscrypt_is_nokey_name(const struct dentry *dentry)
+{
+	return dentry->d_flags & DCACHE_ENCRYPTED_NAME;
+}
+
 /* crypto.c */
 extern void fscrypt_enqueue_decrypt_work(struct work_struct *);
 extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);


Patches currently in stable-queue which might be from ebiggers at kernel.org are

queue-4.19/fscrypt-add-fscrypt_is_nokey_name.patch
queue-4.19/ext4-prevent-creating-duplicate-encrypted-filenames.patch
queue-4.19/ubifs-prevent-creating-duplicate-encrypted-filenames.patch
queue-4.19/f2fs-prevent-creating-duplicate-encrypted-filenames.patch