From: "Theodore Ts'o" <tytso@mit.edu>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2] fscrypt: use READ_ONCE() to access ->i_crypt_info
Date: Tue, 16 Apr 2019 18:57:25 -0400 [thread overview]
Message-ID: <20190416225725.GA14623@mit.edu> (raw)
In-Reply-To: <20190411213215.163929-1-ebiggers@kernel.org>
On Thu, Apr 11, 2019 at 02:32:15PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> ->i_crypt_info starts out NULL and may later be locklessly set to a
> non-NULL value by the cmpxchg() in fscrypt_get_encryption_info().
>
> But ->i_crypt_info is used directly, which technically is incorrect.
> It's a data race, and it doesn't include the data dependency barrier
> needed to safely dereference the pointer on at least one architecture.
>
> Fix this by using READ_ONCE() instead. Note: we don't need to use
> smp_load_acquire(), since dereferencing the pointer only requires a data
> dependency barrier, which is already included in READ_ONCE(). We also
> don't need READ_ONCE() in places where ->i_crypt_info is unconditionally
> dereferenced, since it must have already been checked.
>
> Also downgrade the cmpxchg() to cmpxchg_release(), since RELEASE
> semantics are sufficient on the write side.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
Looks good, applied.
- Ted
prev parent reply other threads:[~2019-04-16 22:57 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-11 21:32 [PATCH v2] fscrypt: use READ_ONCE() to access ->i_crypt_info Eric Biggers
2019-04-16 22:57 ` Theodore Ts'o [this message]
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