From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:45356 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730052AbfJUUtQ (ORCPT ); Mon, 21 Oct 2019 16:49:16 -0400 From: Eric Biggers Subject: [PATCH v2] fscrypt: avoid data race on fscrypt_mode::logged_impl_name Date: Mon, 21 Oct 2019 13:49:03 -0700 Message-Id: <20191021204903.56528-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-fscrypt-owner@vger.kernel.org To: linux-fscrypt@vger.kernel.org Cc: "Theodore Y . Ts'o" , Jaegeuk Kim , linux-kernel@vger.kernel.org List-ID: From: Eric Biggers The access to logged_impl_name is technically a data race, which tools like KCSAN could complain about in the future. See: https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE Fix by using xchg(), which also ensures that only one thread does the logging. This also required switching from bool to int, to avoid a build error on the RISC-V architecture which doesn't implement xchg on bytes. Signed-off-by: Eric Biggers --- fs/crypto/fscrypt_private.h | 2 +- fs/crypto/keysetup.c | 6 ++---- 2 files changed, 3 insertions(+), 5 deletions(-) diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index dacf8fcbac3be..d9a3e8614049f 100644 --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -435,7 +435,7 @@ struct fscrypt_mode { const char *cipher_str; int keysize; int ivsize; - bool logged_impl_name; + int logged_impl_name; }; static inline bool diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index b03b33643e4b2..28bc2da9be3c7 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -81,15 +81,13 @@ struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode, mode->cipher_str, PTR_ERR(tfm)); return tfm; } - if (unlikely(!mode->logged_impl_name)) { + if (!xchg(&mode->logged_impl_name, 1)) { /* * fscrypt performance can vary greatly depending on which * crypto algorithm implementation is used. Help people debug * performance problems by logging the ->cra_driver_name the - * first time a mode is used. Note that multiple threads can - * race here, but it doesn't really matter. + * first time a mode is used. */ - mode->logged_impl_name = true; pr_info("fscrypt: %s using implementation \"%s\"\n", mode->friendly_name, crypto_skcipher_alg(tfm)->base.cra_driver_name); -- 2.23.0.866.gb869b98d4c-goog