Re: [PATCH 3/6] net/tcp-ao: clear the aes_cmac_key when done

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Aug 05, 2026 at 04:36:06PM +0200, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> Clear the local aes_cmac_key structure via __cleanup() function
> when we're done with it to avoid that sensitive data could leak on
> the stack.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  net/ipv4/tcp_ao.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
> index a56bb79e15e0e..12c724fed8a26 100644
> --- a/net/ipv4/tcp_ao.c
> +++ b/net/ipv4/tcp_ao.c
> @@ -141,7 +141,7 @@ void tcp_ao_calc_traffic_key(const struct tcp_ao_key *mkt, u8 *traffic_key,
>  					traffic_key);
>  		return;
>  	case TCP_AO_ALGO_AES_128_CMAC: {
> -		struct aes_cmac_key k;
> +		struct aes_cmac_key k __cleanup(aes_cmac_zeroize_key);
>  
>  		aes_cmac_preparekey(&k, mkt->key, AES_KEYSIZE_128);
>  		aes_cmac(&k, input, input_len, traffic_key);

Similar to the bluetooth patch: This is okay, but it seems the TCP-AO
code has never really tried to do key zeroization, which is why I didn't
include a memzero_explicit() here.  Lots of cases, like the various
traffic key buffers, have never been zeroized and still aren't.

The '__cleanup' trick makes this specific case trivial enough that sure,
it might as well be done anyway.  But it would be nice to have a more
comprehensive patch that actually tried to zeroize all TCP-AO keys.
Otherwise random individual fixes like this trickle in over time and it
takes a lot longer.

- Eric