On Tue, May 12, 2020 at 05:04:05AM +0000, Luis Chamberlain wrote:
> On Mon, May 11, 2020 at 09:03:13PM -0400, Rafael Aquini wrote:
> > On Tue, May 12, 2020 at 12:17:03AM +0000, Luis Chamberlain wrote:
> > > On Mon, May 11, 2020 at 07:59:14PM -0400, Rafael Aquini wrote:
> > > > On Mon, May 11, 2020 at 11:10:45PM +0000, Luis Chamberlain wrote:
> > > > > On Mon, May 11, 2020 at 05:59:04PM -0400, Rafael Aquini wrote:
> > > > > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > > > > > index 8a176d8727a3..f0a4fb38ac62 100644
> > > > > > --- a/kernel/sysctl.c
> > > > > > +++ b/kernel/sysctl.c
> > > > > > @@ -2623,17 +2623,32 @@ static int proc_taint(struct ctl_table *table, int write,
> > > > > > return err;
> > > > > >
> > > > > > if (write) {
> > > > > > + int i;
> > > > > > +
> > > > > > + /*
> > > > > > + * Ignore user input that would make us committing
> > > > > > + * arbitrary invalid TAINT flags in the loop below.
> > > > > > + */
> > > > > > + tmptaint &= (1UL << TAINT_FLAGS_COUNT) - 1;
> > > > >
> > > > > This looks good but we don't pr_warn() of information lost on intention.
> > > > >
> > > >
> > > > Are you thinking in sth like:
> > > >
> > > > + if (tmptaint > TAINT_FLAGS_MAX) {
> > > > + tmptaint &= TAINT_FLAGS_MAX;
> > > > + pr_warn("proc_taint: out-of-range invalid input ignored"
> > > > + " tainted_mask adjusted to 0x%x\n", tmptaint);
> > > > + }
> > > > ?
> > >
> > > Sure that would clarify this.
> > >
> > > > > > +
> > > > > > /*
> > > > > > * Poor man's atomic or. Not worth adding a primitive
> > > > > > * to everyone's atomic.h for this
> > > > > > */
> > > > > > - int i;
> > > > > > for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) {
> > > > > > if ((tmptaint >> i) & 1)
> > > > > > add_taint(i, LOCKDEP_STILL_OK);
> > > > > > }
> > > > > > +
> > > > > > + /*
> > > > > > + * Users with SYS_ADMIN capability can include any arbitrary
> > > > > > + * taint flag by writing to this interface. If that's the case,
> > > > > > + * we also need to mark the kernel "tainted by user".
> > > > > > + */
> > > > > > + add_taint(TAINT_USER, LOCKDEP_STILL_OK);
> > > > >
> > > > > I'm in favor of this however I'd like to hear from Ted on if it meets
> > > > > the original intention. I would think he had a good reason not to add
> > > > > it here.
> > > > >
> > > >
> > > > Fair enough. The impression I got by reading Ted's original commit
> > > > message is that the intent was to have TAINT_USER as the flag set
> > > > via this interface, even though the code was allowing for any
> > > > arbitrary value.
> > >
> > > That wasn't my reading, it was that the user did something very odd
> > > with user input which we don't like as kernel developers, and it gives
> > > us a way to prove: hey you did something stupid, sorry but I cannot
> > > support your kernel panic.
> > >
> > > > I think it's OK to let the user fiddle with
> > > > the flags, as it's been allowed since the introduction of
> > > > this interface, but we need to reflect that fact in the
> > > > tainting itself. Since TAINT_USER is not used anywhere,
> > >
> > > I see users of TAINT_USER sprinkled around
> > >
> >
> > I meant in the original commit that introduced it
> > (commit 34f5a39899f3f3e815da64f48ddb72942d86c366). Sorry I
> > miscomunicated that.
> >
> > In its current usage, it seems that the other places adding TAINT_USER
> > match with what is being proposed here: To signal when we have user
> > fiddling with kernel / module parameters.
>
> drivers/base/regmap/regmap-debugfs.c requires *manual* code changes
> to compile / enable some knob. i915 complains about unsafe module
> params such as module_param_cb_unsafe() core_param_unsafe(). Then
> drivers/soundwire/cadence_master.c is for when a debugfs dangerous
> param was used.
>
> This still doesn't rule out the use of proc_taint() for testing taint,
> and that adding it may break some tests. So even though this would
> only affect some tests scripts, I can't say that adding this taint won't
> cause some headaches to someone. I wouldn't encourage its use on
> proc_taint() from what I can see so far.
>
OK, I´ll repost without the hunk forcing the taint. If we eventually
come to the conclusion that tainting in proc_taint() is the right thing
to do, we can do that part of the change later.
Do you think we should use printk_ratelimited() in the ignore message,
instead?
Cheers,
-- Rafael
