| Message ID | 20220325223824.310119-4-zohar@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ima: support fs-verity digests and signatures | expand |
On Fri, Mar 25, 2022 at 06:38:22PM -0400, Mimi Zohar wrote: > Permit fsverity's file digest (a hash of struct fsverity_digest) to be > included in the IMA measurement list, based on the new measurement > policy rule 'digest_type=verity' option. "fsverity's file digest" *is* 'struct fsverity_digest', not a hash of it. Did you mean to write 'struct fsverity_descriptor'? > diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst > index 1a91d92950a7..2d4789dc7750 100644 > --- a/Documentation/security/IMA-templates.rst > +++ b/Documentation/security/IMA-templates.rst > @@ -68,6 +68,9 @@ descriptors by adding their identifier to the format string > - 'd-ng': the digest of the event, calculated with an arbitrary hash > algorithm (field format: [<hash algo>:]digest, where the digest > prefix is shown only if the hash algorithm is not SHA1 or MD5); > + - 'd-ngv2': same as d-ng, but prefixed with the digest type. > + field format: [<digest type>:<hash algo>:]digest, > + where the digest type is either "ima" or "verity". As in patch 2, it is not clear what the square brackets mean here. Maybe they mean that "<digest type>:<hash algo>:" is optional, but it is not explained when they will be present and when they will not be present. > - 'd-modsig': the digest of the event without the appended modsig; > - 'n-ng': the name of the event, without size limitations; > - 'sig': the file signature, or the EVM portable signature if the file > @@ -106,3 +109,8 @@ currently the following methods are supported: > the ``ima_template=`` parameter; > - register a new template descriptor with custom format through the kernel > command line parameter ``ima_template_fmt=``. > + > + > +References > +========== > +[1] Documentation/filesystems/fsverity.rst Is this meant to be a footnote? There are no references to it above. > @@ -242,14 +267,29 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, > */ > i_version = inode_query_iversion(inode); > hash.hdr.algo = algo; > + hash.hdr.length = hash_digest_size[algo]; > > /* Initialize hash digest to 0's in case of failure */ > memset(&hash.digest, 0, sizeof(hash.digest)); > > - if (buf) > + if (buf) { > result = ima_calc_buffer_hash(buf, size, &hash.hdr); > - else > + } else if (iint->flags & IMA_VERITY_REQUIRED) { > + result = ima_get_verity_digest(iint, &hash); > + switch (result) { > + case 0: > + break; > + case -ENODATA: > + audit_cause = "no-verity-digest"; > + result = -EINVAL; > + break; > + default: > + audit_cause = "invalid-verity-digest"; > + break; > + } > + } else { > result = ima_calc_file_hash(file, &hash.hdr); > + } > > if (result && result != -EBADF && result != -EINVAL) > goto out; The above code only calls ima_get_verity_digest() if 'buf' is non-NULL, otherwise it calls ima_calc_buffer_hash(). Under what circumstances is 'buf' non-NULL? Does this imply that 'digest_type=verity' does not always use verity digests, and if not, when are they used and when are they not used? > +/* > + * Make sure the policy rule and template format are in sync. > + */ > +static void check_template_field(const struct ima_template_desc *template, > + const char *field, const char *msg) > +{ > + int i; > + > + for (i = 0; i < template->num_fields; i++) > + if (!strcmp(template->fields[i]->field_id, field)) > + return; > + > + pr_notice_once("%s", msg); > +} A better description for this function would be something like "Warn if the template does not contain the given field." > index daf49894fd7d..d42a01903f08 100644 > --- a/security/integrity/integrity.h > +++ b/security/integrity/integrity.h > @@ -32,7 +32,7 @@ > #define IMA_HASHED 0x00000200 > > /* iint policy rule cache flags */ > -#define IMA_NONACTION_FLAGS 0xff000000 > +#define IMA_NONACTION_FLAGS 0xff800000 > #define IMA_DIGSIG_REQUIRED 0x01000000 > #define IMA_PERMIT_DIRECTIO 0x02000000 > #define IMA_NEW_FILE 0x04000000 > @@ -40,6 +40,7 @@ > #define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000 > #define IMA_MODSIG_ALLOWED 0x20000000 > #define IMA_CHECK_BLACKLIST 0x40000000 > +#define IMA_VERITY_REQUIRED 0x80000000 It is intentional that the new bit added to IMA_NONACTION_FLAGS is not the same as IMA_VERITY_REQUIRED? - Eric
On Tue, 2022-04-05 at 19:28 +0000, Eric Biggers wrote: > On Fri, Mar 25, 2022 at 06:38:22PM -0400, Mimi Zohar wrote: > > Permit fsverity's file digest (a hash of struct fsverity_digest) to be > > included in the IMA measurement list, based on the new measurement > > policy rule 'digest_type=verity' option. > > "fsverity's file digest" *is* 'struct fsverity_digest', not a hash of it. > Did you mean to write 'struct fsverity_descriptor'? Fixed. > > > diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst > > index 1a91d92950a7..2d4789dc7750 100644 > > --- a/Documentation/security/IMA-templates.rst > > +++ b/Documentation/security/IMA-templates.rst > > @@ -68,6 +68,9 @@ descriptors by adding their identifier to the format string > > - 'd-ng': the digest of the event, calculated with an arbitrary hash > > algorithm (field format: [<hash algo>:]digest, where the digest > > prefix is shown only if the hash algorithm is not SHA1 or MD5); > > + - 'd-ngv2': same as d-ng, but prefixed with the digest type. > > + field format: [<digest type>:<hash algo>:]digest, > > + where the digest type is either "ima" or "verity". > > As in patch 2, it is not clear what the square brackets mean here. Maybe they > mean that "<digest type>:<hash algo>:" is optional, but it is not explained when > they will be present and when they will not be present. Agreed, removed. > > > - 'd-modsig': the digest of the event without the appended modsig; > > - 'n-ng': the name of the event, without size limitations; > > - 'sig': the file signature, or the EVM portable signature if the file > > @@ -106,3 +109,8 @@ currently the following methods are supported: > > the ``ima_template=`` parameter; > > - register a new template descriptor with custom format through the kernel > > command line parameter ``ima_template_fmt=``. > > + > > + > > +References > > +========== > > +[1] Documentation/filesystems/fsverity.rst > > Is this meant to be a footnote? There are no references to it above. > > > @@ -242,14 +267,29 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, > > */ > > i_version = inode_query_iversion(inode); > > hash.hdr.algo = algo; > > + hash.hdr.length = hash_digest_size[algo]; > > > > /* Initialize hash digest to 0's in case of failure */ > > memset(&hash.digest, 0, sizeof(hash.digest)); > > > > - if (buf) > > + if (buf) { > > result = ima_calc_buffer_hash(buf, size, &hash.hdr); > > - else > > + } else if (iint->flags & IMA_VERITY_REQUIRED) { > > + result = ima_get_verity_digest(iint, &hash); > > + switch (result) { > > + case 0: > > + break; > > + case -ENODATA: > > + audit_cause = "no-verity-digest"; > > + result = -EINVAL; > > + break; > > + default: > > + audit_cause = "invalid-verity-digest"; > > + break; > > + } > > + } else { > > result = ima_calc_file_hash(file, &hash.hdr); > > + } > > > > if (result && result != -EBADF && result != -EINVAL) > > goto out; > > The above code only calls ima_get_verity_digest() if 'buf' is non-NULL, > otherwise it calls ima_calc_buffer_hash(). Under what circumstances is 'buf' > non-NULL? Does this imply that 'digest_type=verity' does not always use verity > digests, and if not, when are they used and when are they not used? Agreed, it should always be based on policy. FYI, instead of IMA pre-reading and calculating the file hash, there are instances where the kernel reads the entire file into memory. For example, kernel_read_file() calls security_kernel_post_read_file(), which calls ima_post_read_file(). > > > +/* > > + * Make sure the policy rule and template format are in sync. > > + */ > > +static void check_template_field(const struct ima_template_desc *template, > > + const char *field, const char *msg) > > +{ > > + int i; > > + > > + for (i = 0; i < template->num_fields; i++) > > + if (!strcmp(template->fields[i]->field_id, field)) > > + return; > > + > > + pr_notice_once("%s", msg); > > +} > > A better description for this function would be something like "Warn if the > template does not contain the given field." Ok > > > index daf49894fd7d..d42a01903f08 100644 > > --- a/security/integrity/integrity.h > > +++ b/security/integrity/integrity.h > > @@ -32,7 +32,7 @@ > > #define IMA_HASHED 0x00000200 > > > > /* iint policy rule cache flags */ > > -#define IMA_NONACTION_FLAGS 0xff000000 > > +#define IMA_NONACTION_FLAGS 0xff800000 > > #define IMA_DIGSIG_REQUIRED 0x01000000 > > #define IMA_PERMIT_DIRECTIO 0x02000000 > > #define IMA_NEW_FILE 0x04000000 > > @@ -40,6 +40,7 @@ > > #define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000 > > #define IMA_MODSIG_ALLOWED 0x20000000 > > #define IMA_CHECK_BLACKLIST 0x40000000 > > +#define IMA_VERITY_REQUIRED 0x80000000 > > It is intentional that the new bit added to IMA_NONACTION_FLAGS is not the same > as IMA_VERITY_REQUIRED? Thanks for catching this. Previous versions required an additional bit, but that isn't the case now. thanks, Mimi
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index 839fab811b18..2e0c501ce9c8 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -51,6 +51,9 @@ Description: appraise_flag:= [check_blacklist] Currently, blacklist check is only for files signed with appended signature. + digest_type:= verity + Require fs-verity's file digest instead of the + regular IMA file hash. keyrings:= list of keyrings (eg, .builtin_trusted_keys|.ima). Only valid when action is "measure" and func is KEY_CHECK. @@ -149,3 +152,9 @@ Description: security.ima xattr of a file: appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512 + + Example of a 'measure' rule requiring fs-verity's digests + with indication of type of digest in the measurement list. + + measure func=FILE_CHECK digest_type=verity \ + template=ima-ngv2 diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst index 1a91d92950a7..2d4789dc7750 100644 --- a/Documentation/security/IMA-templates.rst +++ b/Documentation/security/IMA-templates.rst @@ -68,6 +68,9 @@ descriptors by adding their identifier to the format string - 'd-ng': the digest of the event, calculated with an arbitrary hash algorithm (field format: [<hash algo>:]digest, where the digest prefix is shown only if the hash algorithm is not SHA1 or MD5); + - 'd-ngv2': same as d-ng, but prefixed with the digest type. + field format: [<digest type>:<hash algo>:]digest, + where the digest type is either "ima" or "verity". - 'd-modsig': the digest of the event without the appended modsig; - 'n-ng': the name of the event, without size limitations; - 'sig': the file signature, or the EVM portable signature if the file @@ -106,3 +109,8 @@ currently the following methods are supported: the ``ima_template=`` parameter; - register a new template descriptor with custom format through the kernel command line parameter ``ima_template_fmt=``. + + +References +========== +[1] Documentation/filesystems/fsverity.rst diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c index c6805af46211..6bcf42168376 100644 --- a/security/integrity/ima/ima_api.c +++ b/security/integrity/ima/ima_api.c @@ -14,6 +14,7 @@ #include <linux/xattr.h> #include <linux/evm.h> #include <linux/iversion.h> +#include <linux/fsverity.h> #include "ima.h" @@ -200,6 +201,30 @@ int ima_get_action(struct user_namespace *mnt_userns, struct inode *inode, allowed_algos); } +static int ima_get_verity_digest(struct integrity_iint_cache *iint, + struct ima_max_digest_data *hash) +{ + enum hash_algo verity_alg; + int ret; + + ret = fsverity_get_digest(iint->inode, hash->digest, &verity_alg); + if (ret) { + memset(hash->digest, 0, sizeof(hash->digest)); + return ret; + } + + /* + * Unlike in the case of actually calculating the file hash, in + * the fsverity case regardless of the hash algorithm, return + * the verity digest to be included in the measurement list. A + * mismatch between the verity algorithm and the xattr signature + * algorithm, if one exists, will be detected later. + */ + hash->hdr.algo = verity_alg; + hash->hdr.length = hash_digest_size[verity_alg]; + return 0; +} + /* * ima_collect_measurement - collect file measurement * @@ -242,14 +267,29 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, */ i_version = inode_query_iversion(inode); hash.hdr.algo = algo; + hash.hdr.length = hash_digest_size[algo]; /* Initialize hash digest to 0's in case of failure */ memset(&hash.digest, 0, sizeof(hash.digest)); - if (buf) + if (buf) { result = ima_calc_buffer_hash(buf, size, &hash.hdr); - else + } else if (iint->flags & IMA_VERITY_REQUIRED) { + result = ima_get_verity_digest(iint, &hash); + switch (result) { + case 0: + break; + case -ENODATA: + audit_cause = "no-verity-digest"; + result = -EINVAL; + break; + default: + audit_cause = "invalid-verity-digest"; + break; + } + } else { result = ima_calc_file_hash(file, &hash.hdr); + } if (result && result != -EBADF && result != -EINVAL) goto out; diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index a0f3775cbd82..c6b0454b2e25 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -1024,6 +1024,7 @@ enum policy_opt { Opt_fowner_gt, Opt_fgroup_gt, Opt_uid_lt, Opt_euid_lt, Opt_gid_lt, Opt_egid_lt, Opt_fowner_lt, Opt_fgroup_lt, + Opt_digest_type, Opt_appraise_type, Opt_appraise_flag, Opt_appraise_algos, Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings, Opt_label, Opt_err @@ -1066,6 +1067,7 @@ static const match_table_t policy_tokens = { {Opt_egid_lt, "egid<%s"}, {Opt_fowner_lt, "fowner<%s"}, {Opt_fgroup_lt, "fgroup<%s"}, + {Opt_digest_type, "digest_type=%s"}, {Opt_appraise_type, "appraise_type=%s"}, {Opt_appraise_flag, "appraise_flag=%s"}, {Opt_appraise_algos, "appraise_algos=%s"}, @@ -1173,6 +1175,21 @@ static void check_template_modsig(const struct ima_template_desc *template) #undef MSG } +/* + * Make sure the policy rule and template format are in sync. + */ +static void check_template_field(const struct ima_template_desc *template, + const char *field, const char *msg) +{ + int i; + + for (i = 0; i < template->num_fields; i++) + if (!strcmp(template->fields[i]->field_id, field)) + return; + + pr_notice_once("%s", msg); +} + static bool ima_validate_rule(struct ima_rule_entry *entry) { /* Ensure that the action is set and is compatible with the flags */ @@ -1215,7 +1232,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) IMA_INMASK | IMA_EUID | IMA_PCR | IMA_FSNAME | IMA_GID | IMA_EGID | IMA_FGROUP | IMA_DIGSIG_REQUIRED | - IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS)) + IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS | + IMA_VERITY_REQUIRED)) return false; break; @@ -1708,6 +1726,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) LSM_SUBJ_TYPE, AUDIT_SUBJ_TYPE); break; + case Opt_digest_type: + ima_log_string(ab, "digest_type", args[0].from); + if ((strcmp(args[0].from, "verity")) == 0) + entry->flags |= IMA_VERITY_REQUIRED; + else + result = -EINVAL; + break; case Opt_appraise_type: ima_log_string(ab, "appraise_type", args[0].from); if ((strcmp(args[0].from, "imasig")) == 0) @@ -1798,6 +1823,15 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) check_template_modsig(template_desc); } + /* d-ngv2 template field recommended for unsigned fs-verity digests */ + if (!result && entry->action == MEASURE && + entry->flags & IMA_VERITY_REQUIRED) { + template_desc = entry->template ? entry->template : + ima_template_desc_current(); + check_template_field(template_desc, "d-ngv2", + "verity rules should include d-ngv2"); + } + audit_log_format(ab, "res=%d", !result); audit_log_end(ab); return result; @@ -2155,6 +2189,8 @@ int ima_policy_show(struct seq_file *m, void *v) else seq_puts(m, "appraise_type=imasig "); } + if (entry->flags & IMA_VERITY_REQUIRED) + seq_puts(m, "digest_type=verity "); if (entry->flags & IMA_CHECK_BLACKLIST) seq_puts(m, "appraise_flag=check_blacklist "); if (entry->flags & IMA_PERMIT_DIRECTIO) diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c index af269b94b369..590b32b4eedd 100644 --- a/security/integrity/ima/ima_template_lib.c +++ b/security/integrity/ima/ima_template_lib.c @@ -32,12 +32,14 @@ enum data_formats { enum digest_type { DIGEST_TYPE_IMA, + DIGEST_TYPE_VERITY, DIGEST_TYPE__LAST }; -#define DIGEST_TYPE_NAME_LEN_MAX 4 /* including NULL */ +#define DIGEST_TYPE_NAME_LEN_MAX 7 /* including NULL */ static const char * const digest_type_name[DIGEST_TYPE__LAST] = { - [DIGEST_TYPE_IMA] = "ima" + [DIGEST_TYPE_IMA] = "ima", + [DIGEST_TYPE_VERITY] = "verity" }; static int ima_write_template_field_data(const void *data, const u32 datalen, @@ -436,6 +438,8 @@ int ima_eventdigest_ngv2_init(struct ima_event_data *event_data, cur_digestsize = event_data->iint->ima_hash->length; hash_algo = event_data->iint->ima_hash->algo; + if (event_data->iint->flags & IMA_VERITY_REQUIRED) + digest_type = DIGEST_TYPE_VERITY; out: return ima_eventdigest_init_common(cur_digest, cur_digestsize, digest_type, hash_algo, diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index daf49894fd7d..d42a01903f08 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -32,7 +32,7 @@ #define IMA_HASHED 0x00000200 /* iint policy rule cache flags */ -#define IMA_NONACTION_FLAGS 0xff000000 +#define IMA_NONACTION_FLAGS 0xff800000 #define IMA_DIGSIG_REQUIRED 0x01000000 #define IMA_PERMIT_DIRECTIO 0x02000000 #define IMA_NEW_FILE 0x04000000 @@ -40,6 +40,7 @@ #define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000 #define IMA_MODSIG_ALLOWED 0x20000000 #define IMA_CHECK_BLACKLIST 0x40000000 +#define IMA_VERITY_REQUIRED 0x80000000 #define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \ IMA_HASH | IMA_APPRAISE_SUBMASK)
Permit fsverity's file digest (a hash of struct fsverity_digest) to be included in the IMA measurement list, based on the new measurement policy rule 'digest_type=verity' option. To differentiate between a regular IMA file hash from an fsverity's file digest, use the new d-ngv2 format field included in the ima-ngv2 template. The following policy rule requires fsverity file digests and specifies the new 'ima-ngv2' template, which contains the new 'd-ngv2' field. The policy rule may be constrained, for example based on a fsuuid or LSM label. measure func=FILE_CHECK digest_type=verity template=ima-ngv2 Signed-off-by: Mimi Zohar <zohar@linux.ibm.com> --- Documentation/ABI/testing/ima_policy | 9 +++++ Documentation/security/IMA-templates.rst | 8 +++++ security/integrity/ima/ima_api.c | 44 +++++++++++++++++++++-- security/integrity/ima/ima_policy.c | 38 +++++++++++++++++++- security/integrity/ima/ima_template_lib.c | 8 +++-- security/integrity/integrity.h | 3 +- 6 files changed, 104 insertions(+), 6 deletions(-)