On Wed, May 09, 2018 at 07:30:28AM -0400, Mimi Zohar wrote: > On Tue, 2018-05-08 at 17:34 +0000, Luis R. Rodriguez wrote: > > On Thu, May 03, 2018 at 08:24:26PM -0400, Mimi Zohar wrote: > > > On Fri, 2018-05-04 at 00:07 +0000, Luis R. Rodriguez wrote: > > > > On Tue, May 01, 2018 at 09:48:20AM -0400, Mimi Zohar wrote: > > > > > Allow LSMs and IMA to differentiate between signed regulatory.db and > > > > > other firmware. > > > > > > > > > > Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> > > > > > Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx> > > > > > Cc: David Howells <dhowells@xxxxxxxxxx> > > > > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > > > > Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> > > > > > Cc: Johannes Berg <johannes.berg@xxxxxxxxx> > > > > > --- > > > > > drivers/base/firmware_loader/main.c | 5 +++++ > > > > > include/linux/fs.h | 1 + > > > > > 2 files changed, 6 insertions(+) > > > > > > > > > > diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c > > > > > index eb34089e4299..d7cdf04a8681 100644 > > > > > --- a/drivers/base/firmware_loader/main.c > > > > > +++ b/drivers/base/firmware_loader/main.c > > > > > @@ -318,6 +318,11 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv) > > > > > break; > > > > > } > > > > > > > > > > +#ifdef CONFIG_CFG80211_REQUIRE_SIGNED_REGDB > > > > > + if ((strcmp(fw_priv->fw_name, "regulatory.db") == 0) || > > > > > + (strcmp(fw_priv->fw_name, "regulatory.db.p7s") == 0)) > > > > > + id = READING_FIRMWARE_REGULATORY_DB; > > > > > +#endif > > > > > > > > Whoa, no way. > > > > > > There are two methods for the kernel to verify firmware signatures. > > > > Yes, but although CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is its own kernel > > mechanism to verify firmware it uses the request_firmware*() API for > > regulatory.db and regulatory.db.p7s, and IMA already can appraise these two > > files since the firmware API is used. > > IMA-appraisal can verify a signature stored as an xattr, but not a > detached signature. That support could be added, but isn't there > today. Today, a regulatory.db signature would have to be stored as an > xattr. Right, my point was that if someone has IMA installed: a) they would add those xattr to files in /lib/firmware/ already b) upon request_firmware*() calls a security hook would trigger which would enable IMA to appraise those files. So not only would the kernel in turn do double checks on regulatory.db, but also a check on regulatory.db.p7s as well. The difference I suppose is IMA would use a hash function instead of signature check, correct? > > As such I see no reason to add a new ID for them at all. > > K > > Its not providing an *alternative*, its providing an *extra* kernel measure. > > If anything CONFIG_CFG80211_REQUIRE_SIGNED_REGDB perhaps should be its own > > stacked LSM. I'd be open to see patches which set that out. May be a > > cleaner interface. > > > > > If both are enabled, do we require both signatures or is one enough. > > > > Good question. Considering it as a stacked LSM (although not implemented > > as one), I'd say its up to who enabled the Kconfig entries. If IMA and > > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB are enabled then both. If someone enabled > > IMA though, then surely I agree that enabling > > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is stupid and redundant, but its up to the > > system integrator to decide. > > Just because IMA-appraisal is enabled in the kernel doesn't mean that > firmware signatures will be verified. That is a run time policy > decision. Sure, I accept this if IMA does not do signature verification. However signature verification seems like a stackable LSM decision, no? > > If we however want to make it clear that such things as > > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB are not required when IMA is enabled we > > could just make the kconfig depend on !IMA or something? Or perhaps a new > > kconfig for IMA which if selected it means that drivers can opt to open code > > *further* kernel signature verification, even though IMA already is sufficient. > > Perhaps CONFIG_ENABLE_IMA_OVERLAPPING, and the driver depends on it? > > The existing CONFIG_IMA_APPRAISE is not enough. If there was a build > time IMA config that translated into an IMA policy requiring firmware > signature verification (eg. CONFIG_IMA_APPRAISE_FIRMWARE), this could > be sorted out at build time. I see makes sense. > > > Assigning a different id for regdb signed firmware allows LSMs and IMA > > > to handle regdb files differently. > > > > That's not the main concern here, its the precedent we are setting here for > > any new kernel interface which open codes firmware signing on its own. What > > you are doing means other kernel users who open codes their own firmware > > signing may need to add yet-another reading ID. That doesn't either look > > well on code, and seems kind of silly from a coding perspective given > > the above, in which I clarify IMA still is doing its own appraisal on it. > > Suppose, > > 1. Either CONFIG_CFG80211_REQUIRE_SIGNED_REGDB or > "CONFIG_IMA_APPRAISE_FIRMWARE" would be configured at build. > > 2. If CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is configured, not > "CONFIG_IMA_APPRAISE_FIRMWARE", a custom IMA-policy rule that > appraises the firmware signature could be defined. In this case, both > signature verification methods would be enforced. > > then READING_FIRMWARE_REGULATORY_DB would not be needed. True, however I'm suggesting that CONFIG_CFG80211_REQUIRE_SIGNED_REGDB could just be a mini subsystem stackable LSM. Its not clear to me why we need to add a new READING id to any open coded firmware signature checks if we don't have this futuristic option CONFIG_IMA_APPRAISE_FIRMWARE. Yes it provides *more*, but IMA is still seeing the exact file descriptor and do its own thing. Luis
