Re: [PATCH] serial: core: fix suspicious security_locked_down() call

On Fri, May 7, 2021 at 2:27 PM Greg Kroah-Hartman
[off-list ref] wrote:

On Fri, May 07, 2021 at 01:57:19PM +0200, Ondrej Mosnacek wrote:

quoted

The commit that added this check did so in a very strange way - first
security_locked_down() is called, its value stored into retval, and if
it's nonzero, then an additional check is made for (change_irq ||
change_port), and if this is true, the function returns. However, if
the goto exit branch is not taken, the code keeps the retval value and
continues executing the function. Then, depending on whether
uport->ops->verify_port is set, the retval value may or may not be reset
to zero and eventually the error value from security_locked_down() may
abort the function a few lines below.

I will go out on a limb and assume that this isn't the intended behavior
and that an error value from security_locked_down() was supposed to
abort the function only in case (change_irq || change_port) is true.

Are you _sure_ about this?

Verification from the authors and users of this odd feature might be
good to have, as I am loath to change how this works without them
weighing in here.

I'm not completely sure and I'm with you on not merging this without
feedback from people involved in the original patch and/or whoever
understands the logic in said function.

-- 
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.