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
> this change perfectly communicates that fact without
> the need for introducing yet another taint flag.
I'd be happy if we don't have introduce yet-anothe flag as well.
But since Ted introduced it, without using the flag on the proc_taint()
I'd like confirmation we won't screw things up with existing test cases
which assume proc_taint() won't set this up. We'd therefore regress
userspace.
This is why I'd like for us to be careful with this flag.
Luis
