[PATCH net v2 1/2] tls: only install push_pending_record for a TX context

[Rishikesh Jethwani <rjethwani@purestorage.com>]

tls_set_sw_offload() assigns ctx->push_pending_record for both
directions, but the hook is a TX-side dispatcher. On a socket whose TX
side is HW offloaded, tls_set_device_offload() installs
tls_device_push_pending_record(); any later TLS_RX setsockopt
overwrites it with tls_sw_push_pending_record(), because
tls_set_device_offload_rx() itself calls tls_set_sw_offload(sk, 0, NULL)
for the software half of a successful HW RX offload, and so does the
fallback when the RX offload is declined (NIC with TX-only offload,
tls_dev_add() failure).

From then on tls_handle_open_record() (a TLS_SET_RECORD_TYPE cmsg after
a MSG_MORE send, or the close path with a pending writer) runs
tls_sw_push_pending_record() against priv_ctx_tx, which is a
struct tls_offload_context_tx, not a struct tls_sw_context_tx, and
reads open_rec from inside the offload context. On x86_64 without lock
debugging that field overlays sg_tx_data[2].dma_address, which is never
set, so the push is silently skipped and the data buffered by the
MSG_MORE send is later sent under the cmsg's record type, e.g.
application data in a handshake or alert record. Enabling
CONFIG_DEBUG_SPINLOCK, CONFIG_DEBUG_LOCK_ALLOC and CONFIG_LOCKDEP, but
not CONFIG_LOCK_STAT, in the tested x86_64 configuration moves open_rec
over sg_tx_data[5].page_link. Once populated, its page pointer and
scatterlist flags are interpreted as a tls_rec pointer and dereferenced
while reading msg_plaintext.sg.size.

Only set the hook when initialising the TX side.

Found by code review while developing TLS 1.3 HW offload rekey support.

Tested with HW TLS TX and RX offload on Mellanox ConnectX-6 Dx (Crypto
Enabled): after setting TLS_RX, send() "AAAA" with MSG_MORE, then
sendmsg() "BBBB" with a TLS_SET_RECORD_TYPE cmsg for a handshake
record. Without this patch the peer receives a single handshake record
"AAAABBBB"; with it, an application data record "AAAA" followed by a
handshake record "BBBB".

Fixes: e8f69799810c ("net/tls: Add generic NIC offload infrastructure")
Cc: stable@vger.kernel.org
Signed-off-by: Rishikesh Jethwani <rjethwani@purestorage.com>
---
 net/tls/tls_sw.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index d1ad31986cf2..235b868facfa 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -2591,7 +2591,8 @@ int tls_set_sw_offload(struct sock *sk, int tx,
 		}
 	}
 
-	ctx->push_pending_record = tls_sw_push_pending_record;
+	if (tx)
+		ctx->push_pending_record = tls_sw_push_pending_record;
 
 	/* setkey is the last operation that could fail during a
 	 * rekey. if it succeeds, we can start modifying the
-- 
2.50.1