[PATCH 5.2 132/135] net/tls: prevent skb_orphan() from leaking TLS plain text with offload

From: Sasha Levin
Date: Thu Aug 22 2019 - 13:10:26 EST

From: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>

[ Upstream commit 414776621d1006e57e80e6db7fdc3837897aaa64 ]

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).

See commit 0608c69c9a80 ("bpf: sk_msg, sock{map|hash} redirect
through ULP") for justification why the internal flag is safe.
The only location which could leak the flag in is tcp_bpf_sendmsg(),
which is taken care of by clearing the previously unused bit.

v2:
- remove superfluous decrypted mark copy (Willem);
- remove the stale doc entry (Boris);
- rely entirely on EOR marking to prevent coalescing (Boris);
- use an internal sendpages flag instead of marking the socket
(Boris).
v3 (Willem):
- reorganize the can_skb_orphan_partial() condition;
- fix the flag leak-in through tcp_bpf_sendmsg.

Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Reviewed-by: Boris Pismenny <borisp@xxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
Documentation/networking/tls-offload.rst | 18 ------------------
include/linux/skbuff.h | 8 ++++++++
include/linux/socket.h | 3 +++
include/net/sock.h | 10 +++++++++-
net/core/sock.c | 19 ++++++++++++++-----
net/ipv4/tcp.c | 3 +++
net/ipv4/tcp_bpf.c | 6 +++++-
net/ipv4/tcp_output.c | 3 +++
net/tls/tls_device.c | 9 +++++++--
9 files changed, 52 insertions(+), 27 deletions(-)

diff --git a/Documentation/networking/tls-offload.rst b/Documentation/networking/tls-offload.rst
index cb85af559dff1..178f4104f5cf2 100644
--- a/Documentation/networking/tls-offload.rst
+++ b/Documentation/networking/tls-offload.rst
@@ -445,24 +445,6 @@ These flags will be acted upon accordingly by the core ``ktls`` code.
TLS device feature flags only control adding of new TLS connection
offloads, old connections will remain active after flags are cleared.

-Known bugs
-==========
-
-skb_orphan() leaks clear text
------------------------------
-
-Currently drivers depend on the :c:member:`sk` member of
-:c:type:`struct sk_buff <sk_buff>` to identify segments requiring
-encryption. Any operation which removes or does not preserve the socket
-association such as :c:func:`skb_orphan` or :c:func:`skb_clone`
-will cause the driver to miss the packets and lead to clear text leaks.
-
-Redirects leak clear text
--------------------------
-
-In the RX direction, if segment has already been decrypted by the device
-and it gets redirected or mirrored - clear text will be transmitted out.
-
.. _pre_tls_data:

Transmission of pre-TLS data
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 056f557d5194e..64fa59b2c8d5a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1358,6 +1358,14 @@ static inline void skb_copy_hash(struct sk_buff *to, const struct sk_buff *from)
to->l4_hash = from->l4_hash;
};

+static inline void skb_copy_decrypted(struct sk_buff *to,
+ const struct sk_buff *from)
+{
+#ifdef CONFIG_TLS_DEVICE
+ to->decrypted = from->decrypted;
+#endif
+}
+
#ifdef NET_SKBUFF_DATA_USES_OFFSET
static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
{
diff --git a/include/linux/socket.h b/include/linux/socket.h
index b57cd8bf96e2b..810d5ec0ada32 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -291,6 +291,9 @@ struct ucred {
#define MSG_BATCH 0x40000 /* sendmmsg(): more messages coming */
#define MSG_EOF MSG_FIN
#define MSG_NO_SHARED_FRAGS 0x80000 /* sendpage() internal : page frags are not shared */
+#define MSG_SENDPAGE_DECRYPTED 0x100000 /* sendpage() internal : page may carry
+ * plain text and require encryption
+ */

#define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
#define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
diff --git a/include/net/sock.h b/include/net/sock.h
index 6cbc16136357d..526de911cd91d 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2482,6 +2482,7 @@ static inline bool sk_fullsock(const struct sock *sk)

/* Checks if this SKB belongs to an HW offloaded socket
* and whether any SW fallbacks are required based on dev.
+ * Check decrypted mark in case skb_orphan() cleared socket.
*/
static inline struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb,
struct net_device *dev)
@@ -2489,8 +2490,15 @@ static inline struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb,
#ifdef CONFIG_SOCK_VALIDATE_XMIT
struct sock *sk = skb->sk;

- if (sk && sk_fullsock(sk) && sk->sk_validate_xmit_skb)
+ if (sk && sk_fullsock(sk) && sk->sk_validate_xmit_skb) {
skb = sk->sk_validate_xmit_skb(sk, dev, skb);
+#ifdef CONFIG_TLS_DEVICE
+ } else if (unlikely(skb->decrypted)) {
+ pr_warn_ratelimited("unencrypted skb with no associated socket - dropping\n");
+ kfree_skb(skb);
+ skb = NULL;
+#endif
+ }
#endif

return skb;
diff --git a/net/core/sock.c b/net/core/sock.c
index aa4a00d381e38..df7b38b60164f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1988,6 +1988,19 @@ 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
+ return (skb->destructor == sock_wfree ||
+ (IS_ENABLED(CONFIG_INET) && skb->destructor == tcp_wfree));
+}
+
/* This helper is used by netem, as it can hold packets in its
* delay queue. We want to allow the owner socket to send more
* packets, as if they were already TX completed by a typical driver.
@@ -1999,11 +2012,7 @@ void skb_orphan_partial(struct sk_buff *skb)
if (skb_is_tcp_pure_ack(skb))
return;

- if (skb->destructor == sock_wfree
-#ifdef CONFIG_INET
- || skb->destructor == tcp_wfree
-#endif
- ) {
+ if (can_skb_orphan_partial(skb)) {
struct sock *sk = skb->sk;

if (refcount_inc_not_zero(&sk->sk_refcnt)) {
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5264f064a87e3..b30f7f8771817 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -984,6 +984,9 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
if (!skb)
goto wait_for_memory;

+#ifdef CONFIG_TLS_DEVICE
+ skb->decrypted = !!(flags & MSG_SENDPAGE_DECRYPTED);
+#endif
skb_entail(sk, skb);
copy = size_goal;
}
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 3d1e154013844..8a56e09cfb0ed 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -398,10 +398,14 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,
static int tcp_bpf_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
{
struct sk_msg tmp, *msg_tx = NULL;
- int flags = msg->msg_flags | MSG_NO_SHARED_FRAGS;
int copied = 0, err = 0;
struct sk_psock *psock;
long timeo;
+ int flags;
+
+ /* Don't let internal do_tcp_sendpages() flags through */
+ flags = (msg->msg_flags & ~MSG_SENDPAGE_DECRYPTED);
+ flags |= MSG_NO_SHARED_FRAGS;

psock = sk_psock_get(sk);
if (unlikely(!psock))
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7d0be046cbc13..359d298348c72 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1318,6 +1318,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
if (!buff)
return -ENOMEM; /* We'll just try again later. */
+ skb_copy_decrypted(buff, skb);

sk->sk_wmem_queued += buff->truesize;
sk_mem_charge(sk, buff->truesize);
@@ -1872,6 +1873,7 @@ static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
buff = sk_stream_alloc_skb(sk, 0, gfp, true);
if (unlikely(!buff))
return -ENOMEM;
+ skb_copy_decrypted(buff, skb);

sk->sk_wmem_queued += buff->truesize;
sk_mem_charge(sk, buff->truesize);
@@ -2141,6 +2143,7 @@ static int tcp_mtu_probe(struct sock *sk)
sk_mem_charge(sk, nskb->truesize);

skb = tcp_send_head(sk);
+ skb_copy_decrypted(nskb, skb);

TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index eb8f24f420f0f..4cfcce211c2f1 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -342,9 +342,9 @@ static int tls_push_data(struct sock *sk,
struct tls_context *tls_ctx = tls_get_ctx(sk);
struct tls_prot_info *prot = &tls_ctx->prot_info;
struct tls_offload_context_tx *ctx = tls_offload_ctx_tx(tls_ctx);
- int tls_push_record_flags = flags | MSG_SENDPAGE_NOTLAST;
int more = flags & (MSG_SENDPAGE_NOTLAST | MSG_MORE);
struct tls_record_info *record = ctx->open_record;
+ int tls_push_record_flags;
struct page_frag *pfrag;
size_t orig_size = size;
u32 max_open_record_len;
@@ -359,6 +359,9 @@ static int tls_push_data(struct sock *sk,
if (sk->sk_err)
return -sk->sk_err;

+ flags |= MSG_SENDPAGE_DECRYPTED;
+ tls_push_record_flags = flags | MSG_SENDPAGE_NOTLAST;
+
timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
if (tls_is_partially_sent_record(tls_ctx)) {
rc = tls_push_partial_record(sk, tls_ctx, flags);
@@ -545,7 +548,9 @@ void tls_device_write_space(struct sock *sk, struct tls_context *ctx)
gfp_t sk_allocation = sk->sk_allocation;

sk->sk_allocation = GFP_ATOMIC;
- tls_push_partial_record(sk, ctx, MSG_DONTWAIT | MSG_NOSIGNAL);
+ tls_push_partial_record(sk, ctx,
+ MSG_DONTWAIT | MSG_NOSIGNAL |
+ MSG_SENDPAGE_DECRYPTED);
sk->sk_allocation = sk_allocation;
}
}
--
2.20.1