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 ubifs by rejecting no-key dentries in ubifs_create(),
ubifs_mkdir(), ubifs_mknod(), and ubifs_symlink().
Note that ubifs doesn't actually report the duplicate filenames from
readdir, but rather it seems to replace the original dentry with a new
one (which is still wrong, just a different effect from ext4).
On ubifs, this fixes xfstest generic/595 as well as the new xfstest I
wrote specifically for this bug.
Fixes: f4f61d2cc6 ("ubifs: Implement encrypted filenames")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201118075609.120337-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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