| Message ID | 20210210120410.471693-6-mic@digikod.net |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Enable root to update the blacklist keyring | expand |
On Wed, Feb 10, 2021 at 01:04:10PM +0100, Mickaël Salaün wrote: > From: Mickaël Salaün <mic@linux.microsoft.com> > > 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@redhat.com> > Cc: David Woodhouse <dwmw2@infradead.org> > Cc: Eric Snowberg <eric.snowberg@oracle.com> > Cc: Jarkko Sakkinen <jarkko@kernel.org> > Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Tested-by: Jarkko Sakkinen <jarkko@kernel.org> /Jarkko > --- > > 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 139940b54207..555491fdde0e 100644 > --- a/certs/Kconfig > +++ b/certs/Kconfig > @@ -94,4 +94,14 @@ 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 9fe79597bda7..731e8e5bb6d8 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"; > > @@ -78,19 +82,51 @@ 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) > @@ -101,9 +137,8 @@ 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, > }; > > @@ -152,8 +187,7 @@ 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)) { > @@ -172,8 +206,10 @@ 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)); > @@ -247,25 +283,43 @@ int is_binary_blacklisted(const u8 *hash, size_t hash_len) > } > EXPORT_SYMBOL_GPL(is_binary_blacklisted); > > +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"); > + restriction->check = restrict_link_for_blacklist; > + > blacklist_keyring = > keyring_alloc(".blacklist", > GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(), > - (KEY_POS_ALL & ~KEY_POS_SETATTR) | > - KEY_USR_VIEW | KEY_USR_READ | > - KEY_USR_SEARCH, > - KEY_ALLOC_NOT_IN_QUOTA | > + KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | > + KEY_POS_WRITE | > + KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH > +#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE > + | KEY_USR_WRITE > +#endif > + , KEY_ALLOC_NOT_IN_QUOTA | > KEY_ALLOC_SET_KEEP, > - NULL, NULL); > + restriction, NULL); > if (IS_ERR(blacklist_keyring)) > panic("Can't allocate system blacklist keyring\n"); > > -- > 2.30.0 > >
diff --git a/certs/Kconfig b/certs/Kconfig index 139940b54207..555491fdde0e 100644 --- a/certs/Kconfig +++ b/certs/Kconfig @@ -94,4 +94,14 @@ 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 9fe79597bda7..731e8e5bb6d8 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"; @@ -78,19 +82,51 @@ 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) @@ -101,9 +137,8 @@ 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, }; @@ -152,8 +187,7 @@ 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)) { @@ -172,8 +206,10 @@ 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)); @@ -247,25 +283,43 @@ int is_binary_blacklisted(const u8 *hash, size_t hash_len) } EXPORT_SYMBOL_GPL(is_binary_blacklisted); +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"); + restriction->check = restrict_link_for_blacklist; + blacklist_keyring = keyring_alloc(".blacklist", GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(), - (KEY_POS_ALL & ~KEY_POS_SETATTR) | - KEY_USR_VIEW | KEY_USR_READ | - KEY_USR_SEARCH, - KEY_ALLOC_NOT_IN_QUOTA | + KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | + KEY_POS_WRITE | + KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH +#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE + | KEY_USR_WRITE +#endif + , KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_SET_KEEP, - NULL, NULL); + restriction, NULL); if (IS_ERR(blacklist_keyring)) panic("Can't allocate system blacklist keyring\n");