tty: Permit some TIOCL_SETSEL modes without CAP_SYS_ADMIN

With this, processes without CAP_SYS_ADMIN are able to use TIOCLINUX with
subcode TIOCL_SETSEL, in the selection modes TIOCL_SETPOINTER,
TIOCL_SELCLEAR and TIOCL_SELMOUSEREPORT.

TIOCL_SETSEL was previously changed to require CAP_SYS_ADMIN, as this IOCTL
let callers change the selection buffer and could be used to simulate
keypresses.  These three TIOCL_SETSEL selection modes, however, are safe to
use, as they do not modify the selection buffer.

This fixes a mouse support regression that affected Emacs (invisible mouse
cursor).

Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/ee3ec63269b43b34e1c90dd8c9743bf8@finder.org


Fixes: 8d1b43f6 ("tty: Restrict access to TIOCLINUX' copy-and-paste subcommands")
Signed-off-by: Günther Noack <gnoack@google.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20250110142122.1013222-1-gnoack@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>