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Subject[PATCH 3/4] ima: Improvements in ima_appraise_measurement()
Date
From: Mimi Zohar <zohar@linux.vnet.ibm.com>

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 and constify the
cause variable.

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_appraise.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 0c5f94b7b9c3..dd10ecbdce45 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -215,7 +215,7 @@ 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;
@@ -241,16 +241,20 @@ 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_PASS_IMMUTABLE) &&
- (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_PASS_IMMUTABLE:
+ 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) {
case IMA_XATTR_DIGEST_NG:
/* first byte contains algorithm id */
@@ -316,17 +320,20 @@ int ima_appraise_measurement(enum ima_hooks func,
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
op, cause, rc, 0);
} else 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)) {
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 &&
+ xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
status = INTEGRITY_PASS;
}
+
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
op, cause, rc, 0);
} else {
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