[PATCH net 0/3] tls: don't leave keys in kernel memory

[PATCH net 0/3] tls: don't leave keys in kernel memory

[Sabrina Dubroca]

There are a few places where the RX/TX key for a TLS socket is copied
to kernel memory. This series clears those memory areas when they're no
longer needed.

Sabrina Dubroca (3):
  tls: don't copy the key out of tls12_crypto_info_aes_gcm_128
  tls: clear key material from kernel memory when do_tls_setsockopt_conf
    fails
  tls: zero the crypto information from tls_context before freeing

 include/net/tls.h  |  1 +
 net/tls/tls_main.c | 16 +++++++++++++---
 net/tls/tls_sw.c   |  5 +----
 3 files changed, 15 insertions(+), 7 deletions(-)

-- 
2.18.0

[PATCH net 1/3] tls: don't copy the key out of tls12_crypto_info_aes_gcm_128

[Sabrina Dubroca]

There's no need to copy the key to an on-stack buffer before calling
crypto_aead_setkey().

Fixes: 3c4d7559159b ("tls: kernel TLS support")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
 net/tls/tls_sw.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 52fbe727d7c1..268053b04563 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -1130,7 +1130,6 @@ void tls_sw_free_resources_rx(struct sock *sk)
 
 int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
 {
-	char keyval[TLS_CIPHER_AES_GCM_128_KEY_SIZE];
 	struct tls_crypto_info *crypto_info;
 	struct tls12_crypto_info_aes_gcm_128 *gcm_128_info;
 	struct tls_sw_context_tx *sw_ctx_tx = NULL;
@@ -1259,9 +1258,7 @@ int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
 
 	ctx->push_pending_record = tls_sw_push_pending_record;
 
-	memcpy(keyval, gcm_128_info->key, TLS_CIPHER_AES_GCM_128_KEY_SIZE);
-
-	rc = crypto_aead_setkey(*aead, keyval,
+	rc = crypto_aead_setkey(*aead, gcm_128_info->key,
 				TLS_CIPHER_AES_GCM_128_KEY_SIZE);
 	if (rc)
 		goto free_aead;
-- 
2.18.0

[PATCH net 2/3] tls: clear key material from kernel memory when do_tls_setsockopt_conf fails

[Sabrina Dubroca]

Fixes: 3c4d7559159b ("tls: kernel TLS support")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
 net/tls/tls_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
index 180b6640e531..0d432d025471 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -499,7 +499,7 @@ static int do_tls_setsockopt_conf(struct sock *sk, char __user *optval,
 	goto out;
 
 err_crypto_info:
-	memset(crypto_info, 0, sizeof(*crypto_info));
+	memzero_explicit(crypto_info, sizeof(struct tls12_crypto_info_aes_gcm_128));
 out:
 	return rc;
 }
-- 
2.18.0

[PATCH net 3/3] tls: zero the crypto information from tls_context before freeing

[Sabrina Dubroca]

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 <sd@queasysnail.net>
---
 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];
 
 	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(&ctx->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

RE: [PATCH net 3/3] tls: zero the crypto information from tls_context before freeing

[Vakul Garg]

> -----Original Message-----
> From: netdev-owner@vger.kernel.org <netdev-owner@vger.kernel.org> On
> Behalf Of Sabrina Dubroca
> Sent: Wednesday, September 5, 2018 6:52 PM
> To: netdev@vger.kernel.org
> Cc: Sabrina Dubroca <sd@queasysnail.net>; Boris Pismenny
> <borisp@mellanox.com>; Ilya Lesokhin <ilyal@mellanox.com>; Aviad
> Yehezkel <aviadye@mellanox.com>; Dave Watson <davejwatson@fb.com>
> 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 <sd@queasysnail.net>
> ---
>  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(&ctx->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

Re: [PATCH net 2/3] tls: clear key material from kernel memory when do_tls_setsockopt_conf fails

[Boris Pismenny]

Hi Sabrina,

On 9/5/2018 4:21 PM, Sabrina Dubroca wrote:
> Fixes: 3c4d7559159b ("tls: kernel TLS support")
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
> ---
>   net/tls/tls_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> index 180b6640e531..0d432d025471 100644
> --- a/net/tls/tls_main.c
> +++ b/net/tls/tls_main.c
> @@ -499,7 +499,7 @@ static int do_tls_setsockopt_conf(struct sock *sk, char __user *optval,
>   	goto out;
>   
>   err_crypto_info:
> -	memset(crypto_info, 0, sizeof(*crypto_info));
> +	memzero_explicit(crypto_info, sizeof(struct tls12_crypto_info_aes_gcm_128));

Besides the key, there are other (not secret) information in 
tls12_crypto_info_aes_gcm_128. I'd prefer you do not delete it to enable 
users to obtain it (using getsockopt) in case we decide to implement a 
fallback to userspace in the future. Such a fallback must obtain the 
kernel's iv, and record sequence number.

Thanks,
Boris.

Re: [PATCH net 3/3] tls: zero the crypto information from tls_context before freeing

[Sabrina Dubroca]

2018-09-05, 13:48:48 +0000, Vakul Garg wrote:
> 
> 
> > -----Original Message-----
> > From: netdev-owner@vger.kernel.org <netdev-owner@vger.kernel.org> On
> > Behalf Of Sabrina Dubroca
> > Sent: Wednesday, September 5, 2018 6:52 PM
> > To: netdev@vger.kernel.org
> > Cc: Sabrina Dubroca <sd@queasysnail.net>; Boris Pismenny
> > <borisp@mellanox.com>; Ilya Lesokhin <ilyal@mellanox.com>; Aviad
> > Yehezkel <aviadye@mellanox.com>; Dave Watson <davejwatson@fb.com>
> > 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 <sd@queasysnail.net>
> > ---
> >  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 2/3] tls: clear key material from kernel memory when do_tls_setsockopt_conf fails

[Sabrina Dubroca]

2018-09-05, 16:53:54 +0300, Boris Pismenny wrote:
> Hi Sabrina,
> 
> On 9/5/2018 4:21 PM, Sabrina Dubroca wrote:
> > Fixes: 3c4d7559159b ("tls: kernel TLS support")
> > Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
> > ---
> >   net/tls/tls_main.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> > index 180b6640e531..0d432d025471 100644
> > --- a/net/tls/tls_main.c
> > +++ b/net/tls/tls_main.c
> > @@ -499,7 +499,7 @@ static int do_tls_setsockopt_conf(struct sock *sk, char __user *optval,
> >   	goto out;
> >   err_crypto_info:
> > -	memset(crypto_info, 0, sizeof(*crypto_info));
> > +	memzero_explicit(crypto_info, sizeof(struct tls12_crypto_info_aes_gcm_128));
> 
> Besides the key, there are other (not secret) information in
> tls12_crypto_info_aes_gcm_128. I'd prefer you do not delete it to enable
> users to obtain it (using getsockopt) in case we decide to implement a
> fallback to userspace in the future. Such a fallback must obtain the
> kernel's iv, and record sequence number.

The operation failed. There's no reason for this stale data to remain
in the kernel. And you couldn't recover it with getsockopt, because
you'll hit !TLS_CRYPTO_INFO_READY, since we're already resetting
tls_crypto_info. Resetting tls_crypto_info on failure is necessary,
otherwise your socket will be in a broken state, with TLS not setup
but unable to perform a new attempt.

Userspace already has all this information anyway, since it passed it
to the kernel, so why would it need to recover it from the kernel?

-- 
Sabrina