docs: networking: convert secid.txt to ReST

Not much to be done here:
- add SPDX header;
- add a document title;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/networking/secid.rst b/Documentation/networking/secid.rst
new file mode 100644
index 000000000000..b45141a98027
--- /dev/null
+++ b/Documentation/networking/secid.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+LSM/SeLinux secid
+=================
+
+flowi structure:
+
+The secid member in the flow structure is used in LSMs (e.g. SELinux) to indicate
+the label of the flow. This label of the flow is currently used in selecting
+matching labeled xfrm(s).
+
+If this is an outbound flow, the label is derived from the socket, if any, or
+the incoming packet this flow is being generated as a response to (e.g. tcp
+resets, timewait ack, etc.). It is also conceivable that the label could be
+derived from other sources such as process context, device, etc., in special
+cases, as may be appropriate.
+
+If this is an inbound flow, the label is derived from the IPSec security
+associations, if any, used by the packet.