diff options
| -rw-r--r-- | Documentation/ABI/testing/ima_policy | 9 | ||||
| -rw-r--r-- | security/integrity/ima/ima.h | 6 | ||||
| -rw-r--r-- | security/integrity/ima/ima_appraise.c | 29 | ||||
| -rw-r--r-- | security/integrity/ima/ima_main.c | 2 | ||||
| -rw-r--r-- | security/integrity/ima/ima_policy.c | 76 |
5 files changed, 104 insertions, 18 deletions
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index b0e3d278e799..5c2798534950 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -30,9 +30,10 @@ Description: [appraise_flag=] [appraise_algos=] [keyrings=] base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK] - [FIRMWARE_CHECK] + [FIRMWARE_CHECK] [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK] [KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA] + [SETXATTR_CHECK] mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND] [[^]MAY_EXEC] fsmagic:= hex value @@ -138,3 +139,9 @@ Description: keys added to .builtin_trusted_keys or .ima keyring: measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima + + Example of the special SETXATTR_CHECK appraise rule, that + restricts the hash algorithms allowed when writing to the + security.ima xattr of a file: + + appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512 diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index bcaf818fb647..be965a8715e4 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -46,6 +46,9 @@ enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 }; /* current content of the policy */ extern int ima_policy_flag; +/* bitset of digests algorithms allowed in the setxattr hook */ +extern atomic_t ima_setxattr_allowed_hash_algorithms; + /* set during initialization */ extern int ima_hash_algo __ro_after_init; extern int ima_sha1_idx __ro_after_init; @@ -198,6 +201,7 @@ static inline unsigned int ima_hash_key(u8 *digest) hook(KEXEC_CMDLINE, kexec_cmdline) \ hook(KEY_CHECK, key) \ hook(CRITICAL_DATA, critical_data) \ + hook(SETXATTR_CHECK, setxattr_check) \ hook(MAX_CHECK, none) #define __ima_hook_enumify(ENUM, str) ENUM, @@ -288,7 +292,7 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode, const char *func_data, unsigned int *allowed_algos); void ima_init_policy(void); void ima_update_policy(void); -void ima_update_policy_flag(void); +void ima_update_policy_flags(void); ssize_t ima_parse_add_rule(char *); void ima_delete_rules(void); int ima_check_policy(void); diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index e2edef8a9185..8f1eb7ef041e 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -595,12 +595,32 @@ static int validate_hash_algo(struct dentry *dentry, { char *path = NULL, *pathbuf = NULL; enum hash_algo xattr_hash_algo; + const char *errmsg = "unavailable-hash-algorithm"; + unsigned int allowed_hashes; xattr_hash_algo = ima_get_hash_algo(xattr_value, xattr_value_len); - if (likely(xattr_hash_algo == ima_hash_algo || - crypto_has_alg(hash_algo_name[xattr_hash_algo], 0, 0))) - return 0; + allowed_hashes = atomic_read(&ima_setxattr_allowed_hash_algorithms); + + if (allowed_hashes) { + /* success if the algorithm is allowed in the ima policy */ + if (allowed_hashes & (1U << xattr_hash_algo)) + return 0; + + /* + * We use a different audit message when the hash algorithm + * is denied by a policy rule, instead of not being built + * in the kernel image + */ + errmsg = "denied-hash-algorithm"; + } else { + if (likely(xattr_hash_algo == ima_hash_algo)) + return 0; + + /* allow any xattr using an algorithm built in the kernel */ + if (crypto_has_alg(hash_algo_name[xattr_hash_algo], 0, 0)) + return 0; + } pathbuf = kmalloc(PATH_MAX, GFP_KERNEL); if (!pathbuf) @@ -609,8 +629,7 @@ static int validate_hash_algo(struct dentry *dentry, path = dentry_path(dentry, pathbuf, PATH_MAX); integrity_audit_msg(AUDIT_INTEGRITY_DATA, d_inode(dentry), path, - "set_data", "unavailable-hash-algorithm", - -EACCES, 0); + "set_data", errmsg, -EACCES, 0); kfree(pathbuf); diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index af6367ba34ee..a734f7d5292c 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -1051,7 +1051,7 @@ static int __init init_ima(void) pr_warn("Couldn't register LSM notifier, error %d\n", error); if (!error) - ima_update_policy_flag(); + ima_update_policy_flags(); return error; } diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index cb86da0e562b..9eaa509f487a 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -53,6 +53,8 @@ int ima_policy_flag; static int temp_ima_appraise; static int build_ima_appraise __ro_after_init; +atomic_t ima_setxattr_allowed_hash_algorithms; + #define MAX_LSM_RULES 6 enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE, LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE @@ -720,24 +722,57 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode, return action; } -/* - * Initialize the ima_policy_flag variable based on the currently - * loaded policy. Based on this flag, the decision to short circuit - * out of a function or not call the function in the first place - * can be made earlier. +/** + * ima_update_policy_flags() - Update global IMA variables + * + * Update ima_policy_flag and ima_setxattr_allowed_hash_algorithms + * based on the currently loaded policy. + * + * With ima_policy_flag, the decision to short circuit out of a function + * or not call the function in the first place can be made earlier. + * + * With ima_setxattr_allowed_hash_algorithms, the policy can restrict the + * set of hash algorithms accepted when updating the security.ima xattr of + * a file. + * + * Context: called after a policy update and at system initialization. */ -void ima_update_policy_flag(void) +void ima_update_policy_flags(void) { struct ima_rule_entry *entry; + int new_policy_flag = 0; + rcu_read_lock(); list_for_each_entry(entry, ima_rules, list) { + /* + * SETXATTR_CHECK rules do not implement a full policy check + * because rule checking would probably have an important + * performance impact on setxattr(). As a consequence, only one + * SETXATTR_CHECK can be active at a given time. + * Because we want to preserve that property, we set out to use + * atomic_cmpxchg. Either: + * - the atomic was non-zero: a setxattr hash policy is + * already enforced, we do nothing + * - the atomic was zero: no setxattr policy was set, enable + * the setxattr hash policy + */ + if (entry->func == SETXATTR_CHECK) { + atomic_cmpxchg(&ima_setxattr_allowed_hash_algorithms, + 0, entry->allowed_algos); + /* SETXATTR_CHECK doesn't impact ima_policy_flag */ + continue; + } + if (entry->action & IMA_DO_MASK) - ima_policy_flag |= entry->action; + new_policy_flag |= entry->action; } + rcu_read_unlock(); ima_appraise |= (build_ima_appraise | temp_ima_appraise); if (!ima_appraise) - ima_policy_flag &= ~IMA_APPRAISE; + new_policy_flag &= ~IMA_APPRAISE; + + ima_policy_flag = new_policy_flag; } static int ima_appraise_flag(enum ima_hooks func) @@ -903,7 +938,9 @@ void __init ima_init_policy(void) ARRAY_SIZE(critical_data_rules), IMA_DEFAULT_POLICY); - ima_update_policy_flag(); + atomic_set(&ima_setxattr_allowed_hash_algorithms, 0); + + ima_update_policy_flags(); } /* Make sure we have a valid policy, at least containing some rules. */ @@ -943,7 +980,7 @@ void ima_update_policy(void) */ kfree(arch_policy_entry); } - ima_update_policy_flag(); + ima_update_policy_flags(); /* Custom IMA policy has been loaded */ ima_process_queued_keys(); @@ -1177,6 +1214,23 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) return false; break; + case SETXATTR_CHECK: + /* any action other than APPRAISE is unsupported */ + if (entry->action != APPRAISE) + return false; + + /* SETXATTR_CHECK requires an appraise_algos parameter */ + if (!(entry->flags & IMA_VALIDATE_ALGOS)) + return false; + + /* + * full policies are not supported, they would have too + * much of a performance impact + */ + if (entry->flags & ~(IMA_FUNC | IMA_VALIDATE_ALGOS)) + return false; + + break; default: return false; } @@ -1332,6 +1386,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) entry->func = KEY_CHECK; else if (strcmp(args[0].from, "CRITICAL_DATA") == 0) entry->func = CRITICAL_DATA; + else if (strcmp(args[0].from, "SETXATTR_CHECK") == 0) + entry->func = SETXATTR_CHECK; else result = -EINVAL; if (!result) |