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    SubjectRe: [PATCH V34 19/29] Lock down module params that specify hardware parameters (eg. ioport)
    Date
    Matthew Garrett <matthewgarrett@google.com> writes:

    > From: David Howells <dhowells@redhat.com>
    >
    > Provided an annotation for module parameters that specify hardware
    > parameters (such as io ports, iomem addresses, irqs, dma channels, fixed
    > dma buffers and other types).
    >
    > Suggested-by: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
    > Signed-off-by: David Howells <dhowells@redhat.com>
    > Signed-off-by: Matthew Garrett <mjg59@google.com>
    > ---
    > include/linux/security.h | 1 +
    > kernel/params.c | 27 ++++++++++++++++++++++-----
    > security/lockdown/lockdown.c | 1 +
    > 3 files changed, 24 insertions(+), 5 deletions(-)
    >
    > diff --git a/include/linux/security.h b/include/linux/security.h
    > index 61e3f4a62d16..88064d7f6827 100644
    > --- a/include/linux/security.h
    > +++ b/include/linux/security.h
    > @@ -92,6 +92,7 @@ enum lockdown_reason {
    > LOCKDOWN_ACPI_TABLES,
    > LOCKDOWN_PCMCIA_CIS,
    > LOCKDOWN_TIOCSSERIAL,
    > + LOCKDOWN_MODULE_PARAMETERS,
    > LOCKDOWN_INTEGRITY_MAX,
    > LOCKDOWN_CONFIDENTIALITY_MAX,
    > };
    > diff --git a/kernel/params.c b/kernel/params.c
    > index ce89f757e6da..f94fe79e331d 100644
    > --- a/kernel/params.c
    > +++ b/kernel/params.c
    > @@ -24,6 +24,7 @@
    > #include <linux/err.h>
    > #include <linux/slab.h>
    > #include <linux/ctype.h>
    > +#include <linux/security.h>
    >
    > #ifdef CONFIG_SYSFS
    > /* Protects all built-in parameters, modules use their own param_lock */
    > @@ -108,13 +109,19 @@ bool parameq(const char *a, const char *b)
    > return parameqn(a, b, strlen(a)+1);
    > }
    >
    > -static void param_check_unsafe(const struct kernel_param *kp)
    > +static bool param_check_unsafe(const struct kernel_param *kp,
    > + const char *doing)
    > {
    > if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
    > pr_notice("Setting dangerous option %s - tainting kernel\n",
    > kp->name);
    > add_taint(TAINT_USER, LOCKDEP_STILL_OK);
    > }
    > +
    > + if (kp->flags & KERNEL_PARAM_FL_HWPARAM &&
    > + security_locked_down(LOCKDOWN_MODULE_PARAMETERS))
    > + return false;
    > + return true;
    > }

    Should this test occur before tainting the kernel?

    Regards,
    Daniel

    >
    > static int parse_one(char *param,
    > @@ -144,8 +151,10 @@ static int parse_one(char *param,
    > pr_debug("handling %s with %p\n", param,
    > params[i].ops->set);
    > kernel_param_lock(params[i].mod);
    > - param_check_unsafe(&params[i]);
    > - err = params[i].ops->set(val, &params[i]);
    > + if (param_check_unsafe(&params[i], doing))
    > + err = params[i].ops->set(val, &params[i]);
    > + else
    > + err = -EPERM;
    > kernel_param_unlock(params[i].mod);
    > return err;
    > }
    > @@ -553,6 +562,12 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
    > return count;
    > }
    >
    > +#ifdef CONFIG_MODULES
    > +#define mod_name(mod) (mod)->name
    > +#else
    > +#define mod_name(mod) "unknown"
    > +#endif
    > +
    > /* sysfs always hands a nul-terminated string in buf. We rely on that. */
    > static ssize_t param_attr_store(struct module_attribute *mattr,
    > struct module_kobject *mk,
    > @@ -565,8 +580,10 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
    > return -EPERM;
    >
    > kernel_param_lock(mk->mod);
    > - param_check_unsafe(attribute->param);
    > - err = attribute->param->ops->set(buf, attribute->param);
    > + if (param_check_unsafe(attribute->param, mod_name(mk->mod)))
    > + err = attribute->param->ops->set(buf, attribute->param);
    > + else
    > + err = -EPERM;
    > kernel_param_unlock(mk->mod);
    > if (!err)
    > return len;
    > diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
    > index c89046dc2155..d03c4c296af7 100644
    > --- a/security/lockdown/lockdown.c
    > +++ b/security/lockdown/lockdown.c
    > @@ -28,6 +28,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
    > [LOCKDOWN_ACPI_TABLES] = "modified ACPI tables",
    > [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
    > [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
    > + [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
    > [LOCKDOWN_INTEGRITY_MAX] = "integrity",
    > [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
    > };
    > --
    > 2.22.0.410.gd8fdbe21b5-goog

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