[PATCH 0/5] fscrypt: prevent creating duplicate encrypted filenames

Eric Biggers
2020-11-18T07:58:27Z

This series fixes a longstanding race condition where a duplicate
filename can be created in an encrypted directory if a syscall that
creates a new filename (e.g. open() or mkdir()) races with the
directory's encryption key being added.

To close this race, we need to prevent creating files if the dentry is
still marked as a no-key name. I.e. we need to fail the ->create() (or
other operation that creates a new filename) if the key wasn't available
when doing the dentry lookup earlier in the syscall, even if the key was
concurrently added between the dentry lookup and ->create().

See patch 1 for a more detailed explanation.

Patch 1 introduces a helper function required for the fix. Patches 2-4
fix the bug on ext4, f2fs, and ubifs. Patch 5 is a cleanup.

This fixes xfstest generic/595 on ubifs, but that test was hitting this
bug only accidentally. I've also written a new xfstest which reproduces
this bug on both ext4 and ubifs.

Eric Biggers (5):
fscrypt: add fscrypt_is_nokey_name()
ext4: prevent creating duplicate encrypted filenames
f2fs: prevent creating duplicate encrypted filenames
ubifs: prevent creating duplicate encrypted filenames
fscrypt: remove unnecessary calls to fscrypt_require_key()

fs/crypto/hooks.c | 31 +++++++++++--------------------
fs/ext4/namei.c | 3 +++
fs/f2fs/f2fs.h | 2 ++
fs/ubifs/dir.c | 17 +++++++++++++----
include/linux/fscrypt.h | 37 +++++++++++++++++++++++++++++++++++--
5 files changed, 64 insertions(+), 26 deletions(-)

base-commit: 3ceb6543e9cf6ed87cc1fbc6f23ca2db903564cd