From: "Ard Biesheuvel" <ardb@kernel.org>
To: "Eric Biggers" <ebiggers@kernel.org>, linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org,
"Jason A . Donenfeld" <Jason@zx2c4.com>,
"Herbert Xu" <herbert@gondor.apana.org.au>,
"Theodore Ts'o" <tytso@mit.edu>,
stable@vger.kernel.org
Subject: Re: [PATCH] lib/crypto: chacha - Zeroize permuted_state before it leaves scope
Date: Fri, 27 Mar 2026 17:16:26 +0100 [thread overview]
Message-ID: <dd050a2d-a7fb-41db-9c03-c5e601c752cc@app.fastmail.com> (raw)
In-Reply-To: <20260326032920.39408-1-ebiggers@kernel.org>
On Thu, 26 Mar 2026, at 04:29, Eric Biggers wrote:
> Since the ChaCha permutation is invertible, the local variable
> 'permuted_state' is sufficient to compute the original 'state', and thus
> the key, even after the permutation has been done.
>
> While the kernel is quite inconsistent about zeroizing secrets on the
> stack (and some prominent userspace crypto libraries don't bother at all
> since it's not guaranteed to work anyway), the kernel does try to do it
> as a best practice, especially in cases involving the RNG.
>
> Thus, explicitly zeroize 'permuted_state' before it goes out of scope.
>
> Fixes: c08d0e647305 ("crypto: chacha20 - Add a generic ChaCha20 stream
> cipher implementation")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
>
> This patch is targeting libcrypto-fixes
>
> lib/crypto/chacha-block-generic.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
next prev parent reply other threads:[~2026-03-27 16:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-26 3:29 [PATCH] lib/crypto: chacha - Zeroize permuted_state before it leaves scope Eric Biggers
2026-03-27 16:16 ` Ard Biesheuvel [this message]
2026-03-27 20:42 ` Eric Biggers
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