FAILED: patch "[PATCH] lib/crypto: chacha: Zeroize permuted_state before it leaves" failed to apply to 6.6-stable tree

gregkh
2026-04-07T14:52:59Z

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x e5046823f8fa3677341b541a25af2fcb99a5b1e0
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026040751-ample-purposely-c1e5@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e5046823f8fa3677341b541a25af2fcb99a5b1e0 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@kernel.org>
Date: Wed, 25 Mar 2026 20:29:20 -0700
Subject: [PATCH] lib/crypto: chacha: Zeroize permuted_state before it leaves
scope

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
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20260326032920.39408-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

diff --git a/lib/crypto/chacha-block-generic.c b/lib/crypto/chacha-block-generic.c
index 77f68de71066..4a6d627580cb 100644
--- a/lib/crypto/chacha-block-generic.c
+++ b/lib/crypto/chacha-block-generic.c
@@ -87,6 +87,8 @@ void chacha_block_generic(struct chacha_state *state,
&out[i * sizeof(u32)]);

state->x[12]++;
+
+ chacha_zeroize_state(&permuted_state);
}
EXPORT_SYMBOL(chacha_block_generic);

@@ -110,5 +112,7 @@ void hchacha_block_generic(const struct chacha_state *state,

memcpy(&out[0], &permuted_state.x[0], 16);
memcpy(&out[4], &permuted_state.x[12], 16);
+
+ chacha_zeroize_state(&permuted_state);
}
EXPORT_SYMBOL(hchacha_block_generic);