landlock: Harden sock_is_scoped() against file-less sockets

sock_is_scoped() dereferences other->sk_socket->file->f_cred to read the
peer's Landlock domain when evaluating
LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET, without first checking that the
peer has a backing socket and file.  hook_unix_find() performs the same
dereference for LANDLOCK_ACCESS_FS_RESOLVE_UNIX and does guard it.
Guard it here too and treat a peer with no backing file, such as a
kernel socket created by sock_create_kern(), as unscoped.

This is defensive hardening, not a fix for a reachable bug.  The
unix_stream_connect() and unix_may_send() hooks run with the peer held
under unix_state_lock() and only after the AF_UNIX core has excluded
SOCK_DEAD, and no in-tree code binds a file-less AF_UNIX socket to an
abstract address, so other->sk_socket->file is always valid at these
call sites today.

Cc: Günther Noack <gnoack@google.com>
Link: https://patch.msgid.link/20260703152750.2022878-1-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

0 files changed, 0 insertions, 0 deletions