Messages in this thread | | | Date | Thu, 10 Oct 2013 09:25:24 +1100 | From | Ryan Mallon <> | Subject | Re: [PATCH v3] vsprintf: Check real user/group id for %pK |
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On 10/10/13 09:14, Joe Perches wrote: > On Thu, 2013-10-10 at 09:04 +1100, Ryan Mallon wrote: >> On 10/10/13 09:00, Joe Perches wrote: > [] >>> Move the interrupt tests and pK-error printk >>> into case 1: >>> >>> It's the only case where CAP_SYSLOG needs to be >>> tested so it doesn't need to be above the switch. >> >> Like I said, I think it is useful to do the pK-error check anyway. It is >> checking for internal kernel bugs, since if 'pK-error' ever gets >> printed, then some kernel code is doing the wrong thing. > > I think you don't quite understand how kptr_restrict works. > > If it's 0, then the ptr value is always emitted naturally. > if it's 2, then the ptr value is always emitted as 0.
I understand this.
> >> Therefore, I >> think it is useful to print it always (I would argue it even makes sense >> when kptr_restrict=0). > > How? Maybe it's me that doesn't quite understand.
This check:
if (kptr_restrict && (in_irq() || in_serving_softirq() || in_nmi())) {
Is making sure that you don't have kernel code doing something like this:
irqreturn_t some_irq_handler(int irq, void *data) { struct seq_file *seq = to_seq(data);
seq_printf(seq, "value = %pK\n"); return IRQ_HANDLED; }
Because that obviously won't work when kptr_restrict=1 (because the CAP_SYSLOG check is meaningless). However, the code is broken regardless of the kptr_restrict value. Since the default value of kptr_restrict is 0, this kind of bug can go over-looked because the seq file will print the pointer value correctly when kptr_restrict=0, and it will correctly print 0's when kptr_restrict=2, but it will print 'pK-error' when kptr_restrict=1. Doing the check in all cases makes it more likely that bugs like this get found. In fact, doing something like:
if (WARN_ON(in_irq() || in_serving_softirq() || in_nmi())) {
Might be better, since that will print a stack-trace showing where the offending vsprintf is.
~Ryan
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