Re: [PATCH net 3/3] tls: zero the crypto information from tls_context before freeing
2018-09-05, 13:48:48 +, Vakul Garg wrote:
>
>
> > -Original Message-
> > From: netdev-ow...@vger.kernel.org On
> > Behalf Of Sabrina Dubroca
> > Sent: Wednesday, September 5, 2018 6:52 PM
> > To: netdev@vger.kernel.org
> > Cc: Sabrina Dubroca ; Boris Pismenny
> > ; Ilya Lesokhin ; Aviad
> > Yehezkel ; Dave Watson
> > Subject: [PATCH net 3/3] tls: zero the crypto information from tls_context
> > before freeing
> >
> > This contains key material in crypto_send_aes_gcm_128 and
> > crypto_recv_aes_gcm_128.
> >
> > Fixes: 3c4d7559159b ("tls: kernel TLS support")
> > Signed-off-by: Sabrina Dubroca
> > ---
> > include/net/tls.h | 1 +
> > net/tls/tls_main.c | 14 --
> > 2 files changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/net/tls.h b/include/net/tls.h index
> > d5c683e8bb22..2010d23112f9 100644
> > --- a/include/net/tls.h
> > +++ b/include/net/tls.h
> > @@ -180,6 +180,7 @@ struct tls_context {
> > struct tls_crypto_info crypto_recv;
> > struct tls12_crypto_info_aes_gcm_128
> > crypto_recv_aes_gcm_128;
> > };
> > + char tls_crypto_ctx_end[0];
>
> This makes the key zeroization dependent upon the position of unions
> in structure.
Yes. I could add char tls_crypto_ctx_start[0].
> Can you zeroise the crypto_send, crypto_recv separately using two
> memzero_explicit calls?
It's not crypto_send, it's crypto_send_aes_gcm_128. I don't know how
likely it is that another crypto algorithm will ever be added, but
then you'd have to switch to zeroing that thing.
I had a different version of the patch that gave a name to those
unions, but then I need to change all the references everywhere and
the patch becomes a bit ugly, especially for net.
struct tls_context {
union {
struct tls_crypto_info info;
struct tls12_crypto_info_aes_gcm_128 aes_gcm_128;
} crypto_send;
union {
struct tls_crypto_info info;
struct tls12_crypto_info_aes_gcm_128 aes_gcm_128;
} crypto_recv;
[...]
}
Or even:
union tls_crypto_context {
struct tls_crypto_info info;
struct tls12_crypto_info_aes_gcm_128 aes_gcm_128;
};
struct tls_context {
union tls_crypto_context crypto_send;
union tls_crypto_context crypto_recv;
[...]
}
--
Sabrina
RE: [PATCH net 3/3] tls: zero the crypto information from tls_context before freeing
> -Original Message-
> From: netdev-ow...@vger.kernel.org On
> Behalf Of Sabrina Dubroca
> Sent: Wednesday, September 5, 2018 6:52 PM
> To: netdev@vger.kernel.org
> Cc: Sabrina Dubroca ; Boris Pismenny
> ; Ilya Lesokhin ; Aviad
> Yehezkel ; Dave Watson
> Subject: [PATCH net 3/3] tls: zero the crypto information from tls_context
> before freeing
>
> This contains key material in crypto_send_aes_gcm_128 and
> crypto_recv_aes_gcm_128.
>
> Fixes: 3c4d7559159b ("tls: kernel TLS support")
> Signed-off-by: Sabrina Dubroca
> ---
> include/net/tls.h | 1 +
> net/tls/tls_main.c | 14 --
> 2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/tls.h b/include/net/tls.h index
> d5c683e8bb22..2010d23112f9 100644
> --- a/include/net/tls.h
> +++ b/include/net/tls.h
> @@ -180,6 +180,7 @@ struct tls_context {
> struct tls_crypto_info crypto_recv;
> struct tls12_crypto_info_aes_gcm_128
> crypto_recv_aes_gcm_128;
> };
> + char tls_crypto_ctx_end[0];
This makes the key zeroization dependent upon the position of unions in
structure.
Can you zeroise the crypto_send, crypto_recv separately using two
memzero_explicit calls?
>
> struct list_head list;
> struct net_device *netdev;
> diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c index
> 0d432d025471..d3a57c0b2182 100644
> --- a/net/tls/tls_main.c
> +++ b/net/tls/tls_main.c
> @@ -241,6 +241,16 @@ static void tls_write_space(struct sock *sk)
> ctx->sk_write_space(sk);
> }
>
> +static void tls_ctx_free(struct tls_context *ctx) {
> + if (!ctx)
> + return;
> +
> + memzero_explicit(>crypto_send,
> + offsetof(struct tls_context, tls_crypto_ctx_end));
> + kfree(ctx);
> +}
> +
> static void tls_sk_proto_close(struct sock *sk, long timeout) {
> struct tls_context *ctx = tls_get_ctx(sk); @@ -294,7 +304,7 @@
> static void tls_sk_proto_close(struct sock *sk, long timeout) #else
> {
> #endif
> - kfree(ctx);
> + tls_ctx_free(ctx);
> ctx = NULL;
> }
>
> @@ -305,7 +315,7 @@ static void tls_sk_proto_close(struct sock *sk, long
> timeout)
>* for sk->sk_prot->unhash [tls_hw_unhash]
>*/
> if (free_ctx)
> - kfree(ctx);
> + tls_ctx_free(ctx);
> }
>
> static int do_tls_getsockopt_tx(struct sock *sk, char __user *optval,
> --
> 2.18.0
