lib/crypto: chacha: Zeroize permuted_state before it leaves scope

commit e5046823f8fa3677341b541a25af2fcb99a5b1e0 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/lib/crypto/chacha.c b/lib/crypto/chacha.c
index b748fd3d256e41cb00d9c77fa463d41632769cac..1bff9f2837778f1ebbc17e23e67a208b70df0223 100644 (file)
--- a/lib/crypto/chacha.c
+++ b/lib/crypto/chacha.c
@@ -86,6 +86,8 @@ void chacha_block_generic(u32 *state, u8 *stream, int nrounds)
                put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
 
        state[12]++;
+
+       memzero_explicit(x, sizeof(x));
 }
 EXPORT_SYMBOL(chacha_block_generic);
 
@@ -110,5 +112,7 @@ void hchacha_block_generic(const u32 *state, u32 *stream, int nrounds)
 
        memcpy(&stream[0], &x[0], 16);
        memcpy(&stream[4], &x[12], 16);
+
+       memzero_explicit(x, sizeof(x));
 }
 EXPORT_SYMBOL(hchacha_block_generic);