Messages in this thread | | | Subject | Re: [PATCH] Lock down drivers that can have io ports, io mem, irqs and dma changed | From | Corey Minyard <> | Date | Mon, 28 Nov 2016 16:32:19 -0600 |
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On 11/21/2016 05:10 PM, David Howells wrote: > One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> wrote: > >> You need to filter or lock down kernel module options because a lot of >> modules let you set the I/O port or similar (eg mmio) which means you can >> hack the entire machine with say the 8250 driver just by using it with an >> mmio of the right location to patch the secure state to zero just by >> getting the ability to write to the modules conf file. > Is the attached patch the right sort of idea? [Note that I haven't actually > compiled most of these drivers to check my changes yet.] > > David > ---
snip
> diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c > index a112c0146012..7fb9c299a183 100644 > --- a/drivers/char/ipmi/ipmi_si_intf.c > +++ b/drivers/char/ipmi/ipmi_si_intf.c > @@ -3725,6 +3725,12 @@ static int init_ipmi_si(void) > struct smi_info *e; > enum ipmi_addr_src type = SI_INVALID; > > + if ((num_addrs || num_ports || num_irqs) && > + kernel_is_locked_down()) { > + pr_err(PFX "Kernel is locked down\n"); > + return -EPERM; > + } > + > if (initialized) > return 0; > initialized = 1;
This would prevent any IPMI interface from working if any address was given on the kernel command line. I'm not sure what the best policy is, but that sounds like a possible DOS to me.
Can you put this check in hardcode_find_bmc()? Thats the only place where the hardcoded addresses are used, and a check there won't affect anything else.
Also, the error message sounds a little vague to me. If I was a sysadmin and got this, I wouldn't be sure what was going on. Maybe something like: The kernel is locked down, but hard-coded device addresses were given on the driver command line. Ignoring these, but this is a possible security issue.
That's fairly wordy, but it gets the point across. You could also move the pr_err() into kernel_is_locked_down() and pass in the prefix, since there is basically the same pr_err() after every check.
Thanks,
-corey
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