On Tue, Jul 30, 2019 at 5:13 PM Jakub Kicinski
<jakub.kicin...@netronome.com> wrote:
>
> sk_validate_xmit_skb() and drivers depend on the sk member of
> struct sk_buff to identify segments requiring encryption.
> Any operation which removes or does not preserve the original TLS
> socket such as skb_orphan() or skb_clone() will cause clear text
> leaks.
>
> Make the TCP socket underlying an offloaded TLS connection
> mark all skbs as decrypted, if TLS TX is in offload mode.
> Then in sk_validate_xmit_skb() catch skbs which have no socket
> (or a socket with no validation) and decrypted flag set.
>
> Note that CONFIG_SOCK_VALIDATE_XMIT, CONFIG_TLS_DEVICE and
> sk->sk_validate_xmit_skb are slightly interchangeable right now,
> they all imply TLS offload. The new checks are guarded by
> CONFIG_TLS_DEVICE because that's the option guarding the
> sk_buff->decrypted member.
>
> Second, smaller issue with orphaning is that it breaks
> the guarantee that packets will be delivered to device
> queues in-order. All TLS offload drivers depend on that
> scheduling property. This means skb_orphan_partial()'s
> trick of preserving partial socket references will cause
> issues in the drivers. We need a full orphan, and as a
> result netem delay/throttling will cause all TLS offload
> skbs to be dropped.
>
> Reusing the sk_buff->decrypted flag also protects from
> leaking clear text when incoming, decrypted skb is redirected
> (e.g. by TC).
>
> Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
> ---
> I'm sending this for net-next because of lack of confidence
> in my own abilities. It should apply cleanly to net... :)
>
> Documentation/networking/tls-offload.rst | 9 --------
> include/net/sock.h | 28 +++++++++++++++++++++++-
> net/core/skbuff.c | 3 +++
> net/core/sock.c | 22 ++++++++++++++-----
> net/ipv4/tcp.c | 4 +++-
> net/ipv4/tcp_output.c | 3 +++
> net/tls/tls_device.c | 2 ++
> 7 files changed, 55 insertions(+), 16 deletions(-)
> Redirects leak clear text
> -------------------------
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 228db3998e46..90f3f552c789 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -814,6 +814,7 @@ enum sock_flags {
> SOCK_TXTIME,
> SOCK_XDP, /* XDP is attached */
> SOCK_TSTAMP_NEW, /* Indicates 64 bit timestamps always */
> + SOCK_CRYPTO_TX_PLAIN_TEXT, /* Generate skbs with decrypted flag set */
> };
>
> #define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL <<
> SOCK_TIMESTAMPING_RX_SOFTWARE))
> @@ -2480,8 +2481,26 @@ static inline bool sk_fullsock(const struct sock *sk)
> return (1 << sk->sk_state) & ~(TCPF_TIME_WAIT | TCPF_NEW_SYN_RECV);
> }
>
> +static inline void sk_set_tx_crypto(const struct sock *sk, struct sk_buff
> *skb)
nit: skb_.. instead of sk_.. ?
> +{
> +#ifdef CONFIG_TLS_DEVICE
> + skb->decrypted = sock_flag(sk, SOCK_CRYPTO_TX_PLAIN_TEXT);
> +#endif
> +}
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 0b788df5a75b..9e92684479b9 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3794,6 +3794,9 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
>
> skb_reserve(nskb, headroom);
> __skb_put(nskb, doffset);
> +#ifdef CONFIG_TLS_DEVICE
> + nskb->decrypted = head_skb->decrypted;
> +#endif
decrypted is between header_start and headers_end, so
__copy_skb_header just below should take care of this?
> diff --git a/net/core/sock.c b/net/core/sock.c
> index d57b0cc995a0..b0c10b518e65 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1992,6 +1992,22 @@ void skb_set_owner_w(struct sk_buff *skb, struct sock
> *sk)
> }
> EXPORT_SYMBOL(skb_set_owner_w);
>
> +static bool can_skb_orphan_partial(const struct sk_buff *skb)
> +{
> +#ifdef CONFIG_TLS_DEVICE
> + /* Drivers depend on in-order delivery for crypto offload,
> + * partial orphan breaks out-of-order-OK logic.
> + */
> + if (skb->decrypted)
> + return false;
> +#endif
> +#ifdef CONFIG_INET
> + if (skb->destructor == tcp_wfree)
> + return true;
> +#endif
> + return skb->destructor == sock_wfree;
> +}
> +
Just insert the skb->decrypted check into skb_orphan_partial for less
code churn?
I also think that this is an independent concern from leaking plain
text, so perhaps could be a separate patch.
