FAILED: patch "[PATCH] ext4: prevent creating duplicate encrypted filenames" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 75d18cd1868c2aee43553723872c35d7908f240f Mon Sep 17 00:00:00 2001
From: Eric Biggers <[email protected]>
Date: Tue, 17 Nov 2020 23:56:06 -0800
Subject: [PATCH] ext4: prevent creating duplicate encrypted filenames

As described in "fscrypt: add fscrypt_is_nokey_name()", it's possible to create a duplicate filename in an encrypted directory by creating a file concurrently with adding the directory's encryption key.

Fix this bug on ext4 by rejecting no-key dentries in ext4_add_entry().

Note that the duplicate check in ext4_find_dest_de() sometimes prevented this bug. However in many cases it didn't, since ext4_find_dest_de() doesn't examine every dentry.

index 33509266f5a0..793fc7db9d28 100644
@@ -2195,6 +2195,9 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 	if (!dentry->d_name.len)
 		return -EINVAL;
 
+	if (fscrypt_is_nokey_name(dentry))
+		return -ENOKEY;
+
 #ifdef CONFIG_UNICODE
 	if (sb_has_strict_encoding(sb) && IS_CASEFOLDED(dir) &&
 	    sb->s_encoding && utf8_validate(sb->s_encoding, &dentry->d_name))