[PATCH v5 06/18] ima: Improvements in ima_appraise_measurement

Thiago Jung Bauermann
2017-10-18T00:54:35Z

Replace nested ifs in the EVM xattr verification logic with a switch
statement, making the code easier to understand.

Also, add comments to the if statements in the out section.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
---
security/integrity/ima/ima.h | 5 +++++
security/integrity/ima/ima_appraise.c | 33 ++++++++++++++++++++-------------
2 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index d52b487ad259..4e61d3189b72 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -155,6 +155,11 @@ unsigned long ima_get_binary_runtime_size(void);
int ima_init_template(void);
void ima_init_template_list(void);

+static inline bool is_ima_sig(const struct evm_ima_xattr_data *xattr_value)
+{
+ return xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG;
+}
+
/*
* used to protect h_table and sha_table
*/
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 58c6a60c7e83..2c069f47eeec 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -204,7 +204,7 @@ int ima_appraise_measurement(enum ima_hooks func,
int xattr_len, int opened)
{
static const char op[] = "appraise_data";
- char *cause = "unknown";
+ const char *cause = "unknown";
struct dentry *dentry = file_dentry(file);
struct inode *inode = d_backing_inode(dentry);
enum integrity_status status = INTEGRITY_UNKNOWN;
@@ -229,11 +229,16 @@ int ima_appraise_measurement(enum ima_hooks func,
}

status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
- if (status != INTEGRITY_PASS && status != INTEGRITY_UNKNOWN) {
- if (status == INTEGRITY_NOLABEL || status == INTEGRITY_NOXATTRS)
- cause = "missing-HMAC";
- else if (status == INTEGRITY_FAIL)
- cause = "invalid-HMAC";
+ switch (status) {
+ case INTEGRITY_PASS:
+ case INTEGRITY_UNKNOWN:
+ break;
+ case INTEGRITY_NOXATTRS: /* No EVM protected xattrs. */
+ case INTEGRITY_NOLABEL: /* No security.evm xattr. */
+ cause = "missing-HMAC";
+ goto out;
+ case INTEGRITY_FAIL: /* Invalid HMAC/signature. */
+ cause = "invalid-HMAC";
goto out;
}
switch (xattr_value->type) {
@@ -287,17 +292,19 @@ int ima_appraise_measurement(enum ima_hooks func,

out:
if (status != INTEGRITY_PASS) {
+ /* Fix mode, but don't replace file signatures. */
if ((ima_appraise & IMA_APPRAISE_FIX) &&
- (!xattr_value ||
- xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
+ !is_ima_sig(xattr_value)) {
if (!ima_fix_xattr(dentry, iint))
status = INTEGRITY_PASS;
- } else if (inode->i_size == 0 &&
- (iint->flags & IMA_NEW_FILE) &&
- xattr_value &&
- xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
+ }
+
+ /* Permit new files with file signatures, but without data. */
+ if (inode->i_size == 0 && (iint->flags & IMA_NEW_FILE) &&
+ is_ima_sig(xattr_value)) {
status = INTEGRITY_PASS;
}
+
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
op, cause, rc, 0);
} else {
@@ -404,7 +411,7 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
if (!xattr_value_len || xvalue->type >= IMA_XATTR_LAST)
return -EINVAL;
ima_reset_appraise_flags(d_backing_inode(dentry),
- xvalue->type == EVM_IMA_XATTR_DIGSIG);
+ is_ima_sig(xvalue));
result = 0;
}
return result;