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net/tls: prevent skb_orphan() from leaking TLS plain text with offload

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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 0608c69c9a ("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@netronome.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jakub Kicinski
2019-08-07 17:03:59 -07:00
committed by David S. Miller
parent 0de94de180
commit 414776621d
9 changed files with 52 additions and 27 deletions
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18
Documentation/networking/tls-offload.rst
View File

@@ -506,21 +506,3 @@ Drivers should ignore the changes to TLS the device feature flags.
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.