Messages in this thread | | | Subject | Re: [RFC PATCH v2] fw_lockdown: new micro LSM module to prevent loading unsigned firmware | From | Mimi Zohar <> | Date | Mon, 13 Nov 2017 14:36:47 -0500 |
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On Mon, 2017-11-13 at 20:05 +0100, Luis R. Rodriguez wrote: > On Mon, Nov 13, 2017 at 06:43:34AM -0500, Mimi Zohar wrote:
> > + * fw_lockdown_read_file - prevent loading of unsigned firmware > > + * @file: pointer to firmware > > + * @read_id: caller identifier > > + * > > + * Prevent loading of unsigned firmware in lockdown mode. > > + */ > > +static int fw_lockdown_read_file(struct file *file, enum kernel_read_file_id id) > > +{ > > + if (id == READING_FIRMWARE) { > > + if (!is_ima_appraise_enabled() && > > + kernel_is_locked_down("Loading of unsigned firmware")) > > + return -EACCES; > > + } > > How about just if (id != READING_FIRMWARE) return 0 right away so that > the real code of focus is not always indented.
Sure
> This could let the code > grow nicely. > > What I meant above is later we may extend this with: > > if hash_available() > if !valid_hash() > return -EACCES > else if default_fw_key_available() > if !fw_signed_default_key() > return -EACCES; > > That could be the way we support a default system policy for firmware > signing, and it would not require any modifications to any firmware > API callers. > > Notice though that if we later want to extend support for custom requirements > the semantics behind kernel_read_file() would not suffice to LSMify them, as > such I'd think we'd need another call which lets the security requirements > be passed. > > Its unclear if IMA may want to ignore that criteria, as it does the checks in > userspace.
Huh, I kind of lost you here. What does "it" refer to in the above sentence? IMA is in the kernel. So, who does what checks in userspace?
> If it *can* make use of it, it could do the check-in kernel, of > course.
> > + return 0; > > +} > > + > > +static struct security_hook_list fw_lockdown_hooks[] = { > > + LSM_HOOK_INIT(kernel_read_file, fw_lockdown_read_file) > > +}; > > + > > +static int __init init_fw_lockdown(void) > > +{ > > + security_add_hooks(fw_lockdown_hooks, ARRAY_SIZE(fw_lockdown_hooks), > > + "fw_lockdown"); > > + pr_info("initialized\n"); > > + return 0; > > +} > > + > > +late_initcall(init_fw_lockdown); > > +MODULE_LICENSE("GPL"); > > diff --git a/security/security.c b/security/security.c > > index 4bf0f571b4ef..61a0c95ec687 100644 > > --- a/security/security.c > > +++ b/security/security.c > > @@ -32,7 +32,7 @@ > > #define MAX_LSM_EVM_XATTR 2 > > > > /* Maximum number of letters for an LSM name string */ > > -#define SECURITY_NAME_MAX 10 > > +#define SECURITY_NAME_MAX 15 > > Should this small hunk be a separate atomic patch?
I thought about it, but this is the first and only LSM with a larger name.
Mimi
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