Messages in this thread | | | From | Djalal Harouni <> | Date | Thu, 20 Apr 2017 14:44:53 +0200 | Subject | Re: [kernel-hardening] Re: [PATCH v3 1/2] modules:capabilities: automatic module loading restriction |
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On Thu, Apr 20, 2017 at 4:22 AM, Ben Hutchings <ben@decadent.org.uk> wrote: > On Thu, 2017-04-20 at 00:20 +0200, Djalal Harouni wrote: > [...] >> +modules_autoload: >> + >> +A sysctl to control if modules auto-load feature is allowed or not. >> +This sysctl complements "modules_disabled" which is for all module >> +operations where this flag applies only to automatic module loading. >> +Automatic module loading happens when programs request a kernel feature >> +that is implemented by an unloaded module, the kernel automatically >> +runs the program pointed by "modprobe" sysctl in order to load the >> +corresponding module. >> + >> +When modules_autoload is set to (0), the default, there are no >> +restrictions. >> + >> +When modules_autoload is set to (1), processes must have CAP_SYS_MODULE >> +to be able to trigger a module auto-load operation, or CAP_NET_ADMIN >> +for modules with a 'netdev-%s' alias. >> + >> +When modules_autoload is set to (2), automatic module loading is >> +disabled for all. Once set, this value can not be changed. > > I would expect a parameter 'modules_autoload' to be a boolean, so this > behaviour would be surprising. > > What is the point of mode 2? Why would someone want to set > modules_disabled=0 and modules_autoload=2?
modules_disabled is too restrictive and once set it can't be changed, maybe that's why not all users use it.
With modules_disabled=0 and modules_autoload=2
* The functionality of the system can still be made available. * You only disable automatic module loading * Explicit module load/unload can still happen. Administrators or privileged programs can still explicitly load modules provide a feature without rebooting. * You are able to restrict some applications from inserting new modules at all by also applying a seccomp filter and removing their CAP_SYS_MODULE, where explicit load/unload is still available to others. * You are able to unload an old bad version of the module without rebooting, and maybe load the new version.
> [...] >> --- a/kernel/module.c >> +++ b/kernel/module.c > [...] >> +static int modules_autoload_privileged_access(const char *name) >> +{ >> + if (capable(CAP_SYS_MODULE)) >> + return 0; >> + else if (name && strstr(name, "netdev-") && capable(CAP_NET_ADMIN)) > [...] > > We want a prefix match, so use strncmp() not strstr().
Indeed, will fix it.
Thanks!
> Ben. > > -- > Ben Hutchings > It is easier to change the specification to fit the program than vice > versa. >
-- tixxdz
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