On Mon, Jul 12, 2021 at 07:03:13PM +0200, Mickaël Salaün wrote: > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > > Add a kernel option SYSTEM_BLACKLIST_AUTH_UPDATE to enable the root user > to dynamically add new keys to the blacklist keyring. This enables to > invalidate new certificates, either from being loaded in a keyring, or > from being trusted in a PKCS#7 certificate chain. This also enables to > add new file hashes to be denied by the integrity infrastructure. > > Being able to untrust a certificate which could have normaly been > trusted is a sensitive operation. This is why adding new hashes to the > blacklist keyring is only allowed when these hashes are signed and > vouched by the builtin trusted keyring. A blacklist hash is stored as a > key description. The PKCS#7 signature of this description must be > provided as the key payload. > > Marking a certificate as untrusted should be enforced while the system > is running. It is then forbiden to remove such blacklist keys. > > Update blacklist keyring, blacklist key and revoked certificate access rights: > * allows the root user to search for a specific blacklisted hash, which > make sense because the descriptions are already viewable; > * forbids key update (blacklist and asymmetric ones); > * restricts kernel rights on the blacklist keyring to align with the > root user rights. > > See help in tools/certs/print-cert-tbs-hash.sh . > > Cc: David Howells <dhowells@xxxxxxxxxx> > Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> > Cc: Eric Snowberg <eric.snowberg@xxxxxxxxxx> > Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/20210712170313.884724-6-mic@xxxxxxxxxxx > --- > > Changes since v6: > * Rebase on keys-cve-2020-26541-v3: commit ebd9c2ae369a ("integrity: > Load mokx variables into the blacklist keyring"). > > Changes since v5: > * Rebase on keys-next, fix Kconfig conflict, and update the asymmetric > key rights added to the blacklist keyring by the new > add_key_to_revocation_list(): align with blacklist key rights by > removing KEY_POS_WRITE as a safeguard, and add > KEY_ALLOC_BYPASS_RESTRICTION to not be subject to > restrict_link_for_blacklist() that only allows blacklist key types to > be added to the keyring. > * Change the return code for restrict_link_for_blacklist() from -EPERM > to -EOPNOTSUPP to align with asymmetric key keyrings. > > Changes since v3: > * Update commit message for print-cert-tbs-hash.sh . > > Changes since v2: > * Add comment for blacklist_key_instantiate(). > --- > certs/Kconfig | 10 +++++ > certs/blacklist.c | 96 ++++++++++++++++++++++++++++++++++++----------- > 2 files changed, 85 insertions(+), 21 deletions(-) > > diff --git a/certs/Kconfig b/certs/Kconfig > index 0fbe184ceca5..e0e524b7eff9 100644 > --- a/certs/Kconfig > +++ b/certs/Kconfig > @@ -103,4 +103,14 @@ config SYSTEM_REVOCATION_KEYS > containing X.509 certificates to be included in the default blacklist > keyring. > > +config SYSTEM_BLACKLIST_AUTH_UPDATE > + bool "Allow root to add signed blacklist keys" > + depends on SYSTEM_BLACKLIST_KEYRING > + depends on SYSTEM_DATA_VERIFICATION > + help > + If set, provide the ability to load new blacklist keys at run time if > + they are signed and vouched by a certificate from the builtin trusted > + keyring. The PKCS#7 signature of the description is set in the key > + payload. Blacklist keys cannot be removed. > + > endmenu > diff --git a/certs/blacklist.c b/certs/blacklist.c > index b254c87ceb3a..486ce0dd8e9c 100644 > --- a/certs/blacklist.c > +++ b/certs/blacklist.c > @@ -15,6 +15,7 @@ > #include <linux/err.h> > #include <linux/seq_file.h> > #include <linux/uidgid.h> > +#include <linux/verification.h> > #include <keys/system_keyring.h> > #include "blacklist.h" > #include "common.h" > @@ -26,6 +27,9 @@ > */ > #define MAX_HASH_LEN 128 > > +#define BLACKLIST_KEY_PERM (KEY_POS_SEARCH | KEY_POS_VIEW | \ > + KEY_USR_SEARCH | KEY_USR_VIEW) > + > static const char tbs_prefix[] = "tbs"; > static const char bin_prefix[] = "bin"; > > @@ -80,19 +84,51 @@ static int blacklist_vet_description(const char *desc) > return 0; > } > > -/* > - * The hash to be blacklisted is expected to be in the description. There will > - * be no payload. > - */ > -static int blacklist_preparse(struct key_preparsed_payload *prep) > +static int blacklist_key_instantiate(struct key *key, > + struct key_preparsed_payload *prep) > { > - if (prep->datalen > 0) > - return -EINVAL; > - return 0; > +#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE > + int err; > +#endif > + > + /* Sets safe default permissions for keys loaded by user space. */ > + key->perm = BLACKLIST_KEY_PERM; > + > + /* > + * Skips the authentication step for builtin hashes, they are not > + * signed but still trusted. > + */ > + if (key->flags & (1 << KEY_FLAG_BUILTIN)) > + goto out; > + > +#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE > + /* > + * Verifies the description's PKCS#7 signature against the builtin > + * trusted keyring. > + */ > + err = verify_pkcs7_signature(key->description, > + strlen(key->description), prep->data, prep->datalen, > + NULL, VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL); > + if (err) > + return err; > +#else > + /* > + * It should not be possible to come here because the keyring doesn't > + * have KEY_USR_WRITE and the only other way to call this function is > + * for builtin hashes. > + */ > + WARN_ON_ONCE(1); > + return -EPERM; > +#endif > + > +out: > + return generic_key_instantiate(key, prep); > } > > -static void blacklist_free_preparse(struct key_preparsed_payload *prep) > +static int blacklist_key_update(struct key *key, > + struct key_preparsed_payload *prep) > { > + return -EPERM; > } > > static void blacklist_describe(const struct key *key, struct seq_file *m) > @@ -103,9 +139,8 @@ static void blacklist_describe(const struct key *key, struct seq_file *m) > static struct key_type key_type_blacklist = { > .name = "blacklist", > .vet_description = blacklist_vet_description, > - .preparse = blacklist_preparse, > - .free_preparse = blacklist_free_preparse, > - .instantiate = generic_key_instantiate, > + .instantiate = blacklist_key_instantiate, > + .update = blacklist_key_update, > .describe = blacklist_describe, > }; > > @@ -154,8 +189,7 @@ static int mark_raw_hash_blacklisted(const char *hash) > hash, > NULL, > 0, > - ((KEY_POS_ALL & ~KEY_POS_SETATTR) | > - KEY_USR_VIEW), > + BLACKLIST_KEY_PERM, > KEY_ALLOC_NOT_IN_QUOTA | > KEY_ALLOC_BUILT_IN); > if (IS_ERR(key)) { > @@ -232,8 +266,10 @@ int add_key_to_revocation_list(const char *data, size_t size) > NULL, > data, > size, > - ((KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW), > - KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN); > + KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH > + | KEY_USR_VIEW, > + KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN > + | KEY_ALLOC_BYPASS_RESTRICTION); > > if (IS_ERR(key)) { > pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key)); > @@ -260,25 +296,43 @@ int is_key_on_revocation_list(struct pkcs7_message *pkcs7) > } > #endif > > +static int restrict_link_for_blacklist(struct key *dest_keyring, > + const struct key_type *type, const union key_payload *payload, > + struct key *restrict_key) > +{ > + if (type == &key_type_blacklist) > + return 0; > + return -EOPNOTSUPP; > +} > + > /* > * Initialise the blacklist > */ > static int __init blacklist_init(void) > { > const char *const *bl; > + struct key_restriction *restriction; > > if (register_key_type(&key_type_blacklist) < 0) > panic("Can't allocate system blacklist key type\n"); > > + restriction = kzalloc(sizeof(*restriction), GFP_KERNEL); > + if (!restriction) > + panic("Can't allocate blacklist keyring restriction\n"); This prevents me from taking this to my pull request. In moderns standards, no new BUG_ON(), panic() etc. should never added to the kernel. I missed this in my review. This should rather be e.g. restriction = kzalloc(sizeof(*restriction), GFP_KERNEL); if (!restriction) { pr_err("Can't allocate blacklist keyring restriction\n"); return 0; } Unfortunately I need to drop this patch set, because adding new panic() is simply a no-go. BR, Jarkko
