From 414776621d1006e57e80e6db7fdc3837897aaa64 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Wed, 7 Aug 2019 17:03:59 -0700 Subject: net/tls: prevent skb_orphan() from leaking TLS plain text with offload 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 Acked-by: Willem de Bruijn Reviewed-by: Boris Pismenny Signed-off-by: David S. Miller --- Documentation/networking/tls-offload.rst | 18 ------------------ 1 file changed, 18 deletions(-) (limited to 'Documentation/networking/tls-offload.rst') diff --git a/Documentation/networking/tls-offload.rst b/Documentation/networking/tls-offload.rst index b70b70dc4524..0dd3f748239f 100644 --- a/Documentation/networking/tls-offload.rst +++ b/Documentation/networking/tls-offload.rst @@ -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 ` 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. -- cgit