[PATCH 5.4 64/84] tls: Skip tls_append_frag on zero copy size

[Greg Kroah-Hartman]

From: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>

[ Upstream commit a0df71948e9548de819a6f1da68f5f1742258a52 ]

Calling tls_append_frag when max_open_record_len == record->len might
add an empty fragment to the TLS record if the call happens to be on the
page boundary. Normally tls_append_frag coalesces the zero-sized
fragment to the previous one, but not if it's on page boundary.

If a resync happens then, the mlx5 driver posts dump WQEs in
tx_post_resync_dump, and the empty fragment may become a data segment
with byte_count == 0, which will confuse the NIC and lead to a CQE
error.

This commit fixes the described issue by skipping tls_append_frag on
zero size to avoid adding empty fragments. The fix is not in the driver,
because an empty fragment is hardly the desired behavior.

Fixes: e8f69799810c ("net/tls: Add generic NIC offload infrastructure")
Signed-off-by: Maxim Mikityanskiy <maximmi@xxxxxxxxxx>
Reviewed-by: Tariq Toukan <tariqt@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220426154949.159055-1-maximmi@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/tls/tls_device.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 0f034c3bc37d..abb93f7343c5 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -470,11 +470,13 @@ static int tls_push_data(struct sock *sk,
 		copy = min_t(size_t, size, (pfrag->size - pfrag->offset));
 		copy = min_t(size_t, copy, (max_open_record_len - record->len));
 
-		rc = tls_device_copy_data(page_address(pfrag->page) +
-					  pfrag->offset, copy, msg_iter);
-		if (rc)
-			goto handle_error;
-		tls_append_frag(record, pfrag, copy);
+		if (copy) {
+			rc = tls_device_copy_data(page_address(pfrag->page) +
+						  pfrag->offset, copy, msg_iter);
+			if (rc)
+				goto handle_error;
+			tls_append_frag(record, pfrag, copy);
+		}
 
 		size -= copy;
 		if (!size) {
-- 
2.35.1