On Mon, Jun 10, 2024 at 11:49:21PM +0200, Jann Horn wrote:

On Mon, Jun 10, 2024 at 6:36 PM Mickaël Salaün [off-list ref] wrote:

quoted

On Fri, Jun 07, 2024 at 01:41:39PM -0600, Tahera Fahimi wrote:

quoted

On Fri, Jun 07, 2024 at 10:28:35AM +0200, Günther Noack wrote:

quoted

Is it intentional that you are both restricting the connection and the sending
with the same flag (security_unix_may_send)?  If an existing Unix Domain Socket
gets passed in to a program from the outside (e.g. as stdout), shouldn't it
still be possible that the program enables a Landlock policy and then still
writes to it?  (Does that work?  Am I mis-reading the patch?)

If a passed socket is already connected, then a write/send should work.

If I'm reading unix_dgram_sendmsg() correctly, we'll always hit
security_unix_may_send() for any UNIX socket type other than
SOCK_SEQPACKET (meaning SOCK_STREAM and SOCK_DGRAM), even if the
socket is already connected, and then we'll do the landlock check.
That's probably not the intended behavior for Landlock, unless I'm
misreading the code?

Maybe to get nice semantics it's necessary to add a parameter to
security_unix_may_send() that says whether the destination address
came from the caller or from the socket?

I think it would make sense to ignore connected sockets with
security_unix_may_send() because it should already be controlled by
security_unix_stream_connect().  This would still allow passed/inherited
connected sockets to be used, which is an important feature and would
be consistent with read/write on other passed FDs.  This would not work
with dgram sockets though.

We need tests for this case and with different socket modes (inspired by
the net_test.c:protocol variants).