| Message ID | 20210727102307.552052-4-simon.thoby@viveris.fr (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | IMA: restrict the accepted digest algorithms for the security.ima xattr | expand |
Hi Simon, On Tue, 2021-07-27 at 10:23 +0000, THOBY Simon wrote: > This patch defines a new IMA policy rule option "appraise_hash=", > that restricts the hash algorithms accepted for the extended attribute > security.ima when appraising. "Define ..." > When a policy rule uses the 'appraise_hash' option, appraisal of a > file referenced by that rule will now fail if the digest algorithm > employed to hash the file was not one of those explicitly listed > in the option. In its absence, any hash algorithm compiled in the > kernel will be accepted. > > For example, on a system where SELinux is properly deployed, the rule > appraise func=BPRM_CHECK obj_type=iptables_exec_t appraise_hash=sha256,sha384 > will block the execution of iptables if the xattr security.ima of its > executables were not hashed with either sha256 or sha384. > > Signed-off-by: Simon Thoby <simon.thoby@viveris.fr> > --- > Documentation/ABI/testing/ima_policy | 6 ++- > security/integrity/ima/ima_policy.c | 72 ++++++++++++++++++++++++++-- > 2 files changed, 74 insertions(+), 4 deletions(-) > > diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy > index 070779e8d836..365e4c91719e 100644 > --- a/Documentation/ABI/testing/ima_policy > +++ b/Documentation/ABI/testing/ima_policy > @@ -27,7 +27,7 @@ Description: > lsm: [[subj_user=] [subj_role=] [subj_type=] > [obj_user=] [obj_role=] [obj_type=]] > option: [[appraise_type=]] [template=] [permit_directio] > - [appraise_flag=] [keyrings=] > + [appraise_flag=] [keyrings=] [appraise_hash=] Nit: Probably nicer to keep the "appraise_" options together. How about placing it after "appraise_flag", instead of at the end. > base: > func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] > [FIRMWARE_CHECK] > @@ -55,6 +55,10 @@ Description: > label:= [selinux]|[kernel_info]|[data_label] > data_label:= a unique string used for grouping and limiting critical data. > For example, "selinux" to measure critical data for SELinux. > + appraise_hash:= comma-separated list of hash algorithms > + For example, "sha256,sha512" to only accept to appraise > + files where the security.ima xattr was hashed with one > + of these two algorithms. > > default policy: > # PROC_SUPER_MAGIC > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c > index 344b5b0dc1a1..a7f110cbbff0 100644 > --- a/security/integrity/ima/ima_policy.c > +++ b/security/integrity/ima/ima_policy.c > @@ -92,6 +92,7 @@ struct ima_rule_entry { > struct ima_template_desc *template; > }; > > + Is this extra blank line intentional? > /* > * sanity check in case the kernels gains more hash algorithms that can > * fit in an unsigned int > @@ -962,7 +963,7 @@ enum { > Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt, > Opt_appraise_type, Opt_appraise_flag, > Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings, > - Opt_label, Opt_err > + Opt_label, Opt_appraise_hash, Opt_err Nit: move Opt_appraise_hash after Opt_appraise_type. > }; > > static const match_table_t policy_tokens = { > @@ -1000,6 +1001,7 @@ static const match_table_t policy_tokens = { > {Opt_template, "template=%s"}, > {Opt_keyrings, "keyrings=%s"}, > {Opt_label, "label=%s"}, > + {Opt_appraise_hash, "appraise_hash=%s"}, ditto > {Opt_err, NULL} > }; > > @@ -1125,7 +1127,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) > IMA_UID | IMA_FOWNER | IMA_FSUUID | > IMA_INMASK | IMA_EUID | IMA_PCR | > IMA_FSNAME | IMA_DIGSIG_REQUIRED | > - IMA_PERMIT_DIRECTIO)) > + IMA_PERMIT_DIRECTIO | IMA_VALIDATE_HASH)) > return false; > > break; > @@ -1137,7 +1139,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) > IMA_INMASK | IMA_EUID | IMA_PCR | > IMA_FSNAME | IMA_DIGSIG_REQUIRED | > IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED | > - IMA_CHECK_BLACKLIST)) > + IMA_CHECK_BLACKLIST | IMA_VALIDATE_HASH)) > return false; > > break; > @@ -1187,6 +1189,27 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) > return true; > } > > +static unsigned int ima_parse_appraise_hash(char *arg) > +{ > + unsigned int res = 0; > + char *token; > + > + while ((token = strsep(&arg, ",")) != NULL) { > + int idx = match_string(hash_algo_name, HASH_ALGO__LAST, token); Move the variable definition to the beginning of the function. > + > + if (idx < 0) { > + pr_err("unknown hash algorithm \"%s\", ignoring", > + token); > + continue; > + } > + > + /* Add the hash algorithm to the 'allowed' bitfield */ > + res |= (1U << idx); > + } > + > + return res; > +} > + > static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) > { > struct audit_buffer *ab; > @@ -1204,6 +1227,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) > entry->uid_op = &uid_eq; > entry->fowner_op = &uid_eq; > entry->action = UNKNOWN; > + entry->allowed_hashes = 0; > while ((p = strsep(&rule, " \t")) != NULL) { > substring_t args[MAX_OPT_ARGS]; > int token; > @@ -1556,6 +1580,23 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) > &(template_desc->fields), > &(template_desc->num_fields)); > entry->template = template_desc; > + break; > + case Opt_appraise_hash: ditto "appraise_hash=" should be limited to appraise rules. Please update ima_validate_rule(). thanks, Mimi > + ima_log_string(ab, "appraise_hash", args[0].from); > + > + if (entry->allowed_hashes) { > + result = -EINVAL; > + break; > + } > + > + entry->allowed_hashes = ima_parse_appraise_hash(args[0].from); > + if (!entry->allowed_hashes) { > + result = -EINVAL; > + break; > + } > + > + entry->flags |= IMA_VALIDATE_HASH; > + > break; > case Opt_err: > ima_log_string(ab, "UNKNOWN", p); > <trim>
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index 070779e8d836..365e4c91719e 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -27,7 +27,7 @@ Description: lsm: [[subj_user=] [subj_role=] [subj_type=] [obj_user=] [obj_role=] [obj_type=]] option: [[appraise_type=]] [template=] [permit_directio] - [appraise_flag=] [keyrings=] + [appraise_flag=] [keyrings=] [appraise_hash=] base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] [FIRMWARE_CHECK] @@ -55,6 +55,10 @@ Description: label:= [selinux]|[kernel_info]|[data_label] data_label:= a unique string used for grouping and limiting critical data. For example, "selinux" to measure critical data for SELinux. + appraise_hash:= comma-separated list of hash algorithms + For example, "sha256,sha512" to only accept to appraise + files where the security.ima xattr was hashed with one + of these two algorithms. default policy: # PROC_SUPER_MAGIC diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 344b5b0dc1a1..a7f110cbbff0 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -92,6 +92,7 @@ struct ima_rule_entry { struct ima_template_desc *template; }; + /* * sanity check in case the kernels gains more hash algorithms that can * fit in an unsigned int @@ -962,7 +963,7 @@ enum { Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt, Opt_appraise_type, Opt_appraise_flag, Opt_permit_directio, Opt_pcr, Opt_template, Opt_keyrings, - Opt_label, Opt_err + Opt_label, Opt_appraise_hash, Opt_err }; static const match_table_t policy_tokens = { @@ -1000,6 +1001,7 @@ static const match_table_t policy_tokens = { {Opt_template, "template=%s"}, {Opt_keyrings, "keyrings=%s"}, {Opt_label, "label=%s"}, + {Opt_appraise_hash, "appraise_hash=%s"}, {Opt_err, NULL} }; @@ -1125,7 +1127,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) IMA_UID | IMA_FOWNER | IMA_FSUUID | IMA_INMASK | IMA_EUID | IMA_PCR | IMA_FSNAME | IMA_DIGSIG_REQUIRED | - IMA_PERMIT_DIRECTIO)) + IMA_PERMIT_DIRECTIO | IMA_VALIDATE_HASH)) return false; break; @@ -1137,7 +1139,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) IMA_INMASK | IMA_EUID | IMA_PCR | IMA_FSNAME | IMA_DIGSIG_REQUIRED | IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED | - IMA_CHECK_BLACKLIST)) + IMA_CHECK_BLACKLIST | IMA_VALIDATE_HASH)) return false; break; @@ -1187,6 +1189,27 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) return true; } +static unsigned int ima_parse_appraise_hash(char *arg) +{ + unsigned int res = 0; + char *token; + + while ((token = strsep(&arg, ",")) != NULL) { + int idx = match_string(hash_algo_name, HASH_ALGO__LAST, token); + + if (idx < 0) { + pr_err("unknown hash algorithm \"%s\", ignoring", + token); + continue; + } + + /* Add the hash algorithm to the 'allowed' bitfield */ + res |= (1U << idx); + } + + return res; +} + static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) { struct audit_buffer *ab; @@ -1204,6 +1227,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) entry->uid_op = &uid_eq; entry->fowner_op = &uid_eq; entry->action = UNKNOWN; + entry->allowed_hashes = 0; while ((p = strsep(&rule, " \t")) != NULL) { substring_t args[MAX_OPT_ARGS]; int token; @@ -1556,6 +1580,23 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) &(template_desc->fields), &(template_desc->num_fields)); entry->template = template_desc; + break; + case Opt_appraise_hash: + ima_log_string(ab, "appraise_hash", args[0].from); + + if (entry->allowed_hashes) { + result = -EINVAL; + break; + } + + entry->allowed_hashes = ima_parse_appraise_hash(args[0].from); + if (!entry->allowed_hashes) { + result = -EINVAL; + break; + } + + entry->flags |= IMA_VALIDATE_HASH; + break; case Opt_err: ima_log_string(ab, "UNKNOWN", p); @@ -1714,6 +1755,25 @@ static void ima_show_rule_opt_list(struct seq_file *m, seq_printf(m, "%s%s", i ? "|" : "", opt_list->items[i]); } +static void ima_policy_show_appraise_hash(struct seq_file *m, + unsigned int allowed_hashes) +{ + int idx; + bool first = true; + + for (idx = 0; idx < HASH_ALGO__LAST; idx++) { + if (!(allowed_hashes & (1U << idx))) + continue; + + if (!first) + seq_puts(m, ","); + first = false; + + seq_puts(m, hash_algo_name[idx]); + } + +} + int ima_policy_show(struct seq_file *m, void *v) { struct ima_rule_entry *entry = v; @@ -1825,6 +1885,12 @@ int ima_policy_show(struct seq_file *m, void *v) seq_puts(m, " "); } + if (entry->flags & IMA_VALIDATE_HASH) { + seq_puts(m, "appraise_hash="); + ima_policy_show_appraise_hash(m, entry->allowed_hashes); + seq_puts(m, " "); + } + for (i = 0; i < MAX_LSM_RULES; i++) { if (entry->lsm[i].rule) { switch (i) {
This patch defines a new IMA policy rule option "appraise_hash=", that restricts the hash algorithms accepted for the extended attribute security.ima when appraising. When a policy rule uses the 'appraise_hash' option, appraisal of a file referenced by that rule will now fail if the digest algorithm employed to hash the file was not one of those explicitly listed in the option. In its absence, any hash algorithm compiled in the kernel will be accepted. For example, on a system where SELinux is properly deployed, the rule appraise func=BPRM_CHECK obj_type=iptables_exec_t appraise_hash=sha256,sha384 will block the execution of iptables if the xattr security.ima of its executables were not hashed with either sha256 or sha384. Signed-off-by: Simon Thoby <simon.thoby@viveris.fr> --- Documentation/ABI/testing/ima_policy | 6 ++- security/integrity/ima/ima_policy.c | 72 ++++++++++++++++++++++++++-- 2 files changed, 74 insertions(+), 4 deletions(-)