hulk inclusion category: bugfix
---------------------------
System administrators can require that all accessed files have a signature by specifying appraise_type=imasig in a policy rule.
Currently, only IMA signatures satisfy this requirement. IMA signatures ensure data source authentication for file content and prevent any change. EVM signatures instead ensure data source authentication for file metadata. Given that the digest or signature of the file content must be included in the metadata, EVM signatures provide at least the same guarantees of IMA signatures.
This patch lets systems protected with EVM signatures pass appraisal verification if the appraise_type=imasig requirement is specified in the policy. This facilitates deployment in the scenarios where only EVM signatures are available.
The patch makes the following changes:
file xattr types: security.ima: IMA_XATTR_DIGEST/IMA_XATTR_DIGEST_NG security.evm: EVM_XATTR_PORTABLE_DIGSIG
execve(), mmap(), open() behavior (with appraise_type=imasig): before: denied (file without IMA signature, imasig requirement not met) after: allowed (file with EVM portable signature, imasig requirement met)
open(O_WRONLY) behavior (without appraise_type=imasig): before: allowed (file without IMA signature, not immutable) after: denied (file with EVM portable signature, immutable)
In addition, similarly to IMA signatures, this patch temporarily allows new files without or with incomplete metadata to be opened so that content can be written.
Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- security/integrity/ima/ima_appraise.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index aa847982eb1a..8d61d2266d4d 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -251,6 +251,8 @@ int ima_appraise_measurement(enum ima_hooks func, cause = "missing-HMAC"; goto out; case INTEGRITY_FAIL_IMMUTABLE: + set_bit(IMA_DIGSIG, &iint->atomic_flags); + /* fall through */ case INTEGRITY_FAIL: /* Invalid HMAC/signature. */ cause = "invalid-HMAC"; goto out; @@ -269,12 +271,16 @@ int ima_appraise_measurement(enum ima_hooks func, status = INTEGRITY_FAIL; break; } - if (iint->flags & IMA_DIGSIG_REQUIRED) { - cause = "IMA-signature-required"; - status = INTEGRITY_FAIL; - break; + if (status != INTEGRITY_PASS_IMMUTABLE) { + if (iint->flags & IMA_DIGSIG_REQUIRED) { + cause = "IMA-signature-required"; + status = INTEGRITY_FAIL; + break; + } + clear_bit(IMA_DIGSIG, &iint->atomic_flags); + } else { + set_bit(IMA_DIGSIG, &iint->atomic_flags); } - clear_bit(IMA_DIGSIG, &iint->atomic_flags); if (xattr_len - sizeof(xattr_value->type) - hash_start >= iint->ima_hash->length) /* xattr length may be longer. md5 hash in previous @@ -336,9 +342,9 @@ int ima_appraise_measurement(enum ima_hooks func, status = INTEGRITY_PASS; }
- /* Permit new files with file signatures, but without data. */ + /* Permit new files marked as immutable, but without data. */ if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE && - xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) { + test_bit(IMA_DIGSIG, &iint->atomic_flags)) { status = INTEGRITY_PASS; }